nm0442: today we're going to s-, cover structural and functional relationships 
in proteins [0.5] and i'm sure as most of you will really all be aware this is 
going to be [0.5] er you know we're going to only cover a very small proportion 
of [0.5] of er structural and functional relationships in proteins [1.2] 
proteins are of course the sort of workhorses the machines of the cells [0.3] 
and they perform all of the reactions that are compatible with life including 
those ones [0.4] listed there [0.9] er [1.1] and of course there are very [0.2] 
many relevant medical examples to how [0.3] the structure [0.4] and function of 
a protein [0.3] is related to [0.5] the normal physiology [0.3] is related to a 
disease whereby [0.7] a loss of function results in an important medical 
condition i'm think-, thinking of things like [0.3] cystic fibrosis [0.7] where 
the gain of a function [0.5] is a problem for example a [0.3] tumour [0.5] 
tumour genes [0.3] things like rasp found in a large proportion of [0.3] human 
tumours [0.3] and even when the normal function [0.2] of a protein be-, could 
become a a 
medical problem [0.4] i'm thinking there particularly of things like multidrug 
resistance [0.3] both in bacteria [0.5] and again in tumours [0.7] so [0.3] 
with that in mind [0.3] we will briefly and it will be brief and this is [0.2] 
essentially part of i guess your [0.3] assumed knowledge we'll review the basic 
[0.2] aspects of er protein structure [0.3] and go on to [0.3] some [0.4] 
medically relevant examples [1.6] so the basic [0.6] er unit of protein 
structure is of course the peptide bond [0.8] er [0.6] a polypeptide [0.3] er 
it's a sequence of amino acids [0.3] that are joined through peptide bonds that 
represents the [0.4] the primary structure [0.5] of that protein [0.7] the 
peptide bond is formed through the condensation of a [0.2] carboxylic [0.6] 
acid group from an amino acid [0.4] and a [0.9] amine group from an amino acid 
[1.9] the er carbonyl oxygen [0.6] and the nitrogen [0.5] are electronegative 
and that effectively means that the peptide bond itself [0.3] has extensive 
double-bonded character [0.6] it's rigid and planar [0.5] it can't rotate [1.5] 
but of course there's free rotation [0.5] of the bonds on either side [0.4] of 
that peptide bond [0.6] and so the 
side chains of the amino acids [0.3] could in theory [0.3] form any number of 
angles in relation to that peptide bond [2.4] i'm sure as you know in fact [0.
6] er [0.2] there are relatively few angles [0.3] that are allowed [0.4] on 
either side of that peptide bond [1.5] and most of the angles are not allowed 
because they're sterically unfavourable [0.3] they represent [0.6] clashes 
interactions between [0.5] the er side chains of amino acids [0.5] or the side 
chains of amino acids and the and the polypeptide chain [1.2] and so [0.4] the 
confirmations of the bonds [0.3] on either side of the peptide bond can 
actually [0.3] only form [0.2] relatively few [0.4] what are generally termed 
secondary structures [2.1] the one with the largest scope is the is the beta 
sheet [0.7] er i should say that [0.2] psi and phi are of course the they're 
the names of the two bonds on either side of the peptide bond you don't really 
[0.2] need to know that [0.5] er [0.9] but for a beta sheet [0.4] those psi and 
phi angles suggest that the only [0.3] the favourable [0.2] energetic 
confirmation [0.8] er for the side chains of these amino acids [0.2] would be 
[0.2] if 
they were essentially opposed [0.3] on either side [0.3] of the peptide bond [0.
6] and so they alternate [0.5] on either side of the peptide bond [1.2] er beta 
sheets er the that er opposition of er side chains allows for extensive [0.3] 
hydrogen bonding between [0.5] separate polypeptide chains that are in the beta 
sheet [0.3] confirmation [0.7] and i'm actually not really going to talk much 
more about beta sheets that's not because i don't think they're important [0.4] 
er er or indeed have medically relevant examples it's just there isn't s-, time 
[0.4] within this lecture to really go into beta sheet structures [0.3] other 
than to describe [0.7] er the Ramachandran conditions [1.2] er [0.7] obviously 
there are very [0.3] pertinent examples indeed the transition between alpha 
helical structures and beta pleated sheet structures is pathological in various 
diseases such as Alzheimer's that's that ameloid [0.4] transition [1.8] the 
second set of allowed angles [0.5] on either side of the peptide bond are 
essentially [0.3] er [0.6] offset by about i think about er a hundred-and-ten 
a hundred-and-twenty degrees [0.9] and the only way you can conceptualize the 
arrangement of side chains in a polypeptide that are offset like that is if 
they're essentially rotating and that gives you [0.3] the i-, notion that that 
would be a helix [1.0] you can see there there's one small [0.4] area that's 
allowed if van der Waals' radii [0.2] radii are taken to be a little smaller [0.
3] and that's a left-handed helix [0.5] and we'll talk about that [0.9] er [0.
2] and generally [0.4] er most amino acids [0.2] fall into these Ramachandran 
rules Ramachandran was of course a [0.3] Indian mathematician who who who er 
worked out these rules [0.3] er for a secondary structure [0.5] in the er turn 
of the s-, turn of last century now [0.9] using both mathematical principles 
and er models of peptides [1.0] the only amino acid that can be found in [0.3] 
virtually any [0.5] angle confirmation [0.5] is er is glycine of course and 
that's because it's secondary [0.3] er it's er sorry side chains of course 
hydrogen [2.6] so most proteins contain [0.3] alpha helix and indeed some [0.2] 
are nearly all alpha 
helix [0.4] and [0.2] things like myoglobin and haemoglobin [0.2] are 
predominantly alpha helical [0.4] indeed the [0.3] structures the parts of the 
protein that are not alpha helices [0.3] in myoglobin and haemoglobin [0.4] are 
involved in turning [0.8] the molecule back on itself [0.3] to give [0.2] the 
very characteristic compacted [0.5] shapes of those molecules [1.7] so i'm sure 
that [0.8] oh [0.5] if anybody's struggling with their right-handed and left-
handed helices that's what that's [0.2] there for [1.6] so this then is an 
actual alpha helix [2.4] we can see that er [1.2] the side chains are nicely 
arrayed [0.4] to the outside of the helix on this side and on this side [0.5] 
er that er it being it it being right-handed it pitches essentially from er er 
from the left towards the right upwards [0.5] er in this particular helices you 
can see that there's essentially hydrophobic [0.7] side chains on this side [0.
5] and [0.3] er charged side chains on this side and this gives you an idea as 
to the orientation [0.2] potentially [0.2] of that helix in a protein [0.3] 
obviously the hydrophobic side would be inward-facing [0.5] 
the hydro [0.4] philic side [0.3] would be facing towards the aqueous 
environment [1.3] you can see on the top there the [0.2] how the er [1.3] the 
er side chains essentially [0.2] overlap and the [0.4] er [0.9] array 
themselves such they're approximately four residues apart as they go up [0.7] 
the side of the helix [1.4] so that's as i said there's approximately three-and-
a-half amino acids per turn [1.7] and also you can see that the helices [0.3] 
this arrangement of helices [0.3] allows for hydrogen bonding within the chain 
[1.1] so interchain hydrogen bonding and this helps stabilize the structure and 
it's why helical structures are so [0.4] oft-, alpha helical structure 
energetically very favourable [5.7] so if we look at the primary [0.6] so the 
the the notion that there's periodicity or there appears to be certain 
periodicity [0.2] in helices allows you to look at the primary structure [0.2] 
and make predictions [0.3] as to [0.3] er what the secondary structure is most 
likely to be [0.3] there is frequently periodicity [0.2] in amino acid 
sequences [0.3] er and certain amino acids are indeed 
preferred in helices [0.2] yet others are not preferred in helices [0.6] 
glycine isn't preferred in helices and proline as you know is a [0.5] an amino 
acid that will essentially kink [0.4] a polypeptide chain that won't be found 
in [0.3] helices [4.7] so this then demonstrates with that helices i was just 
showing you that the [0.2] indeed the [0.4] the polar residues [0.4] er the 
sorry the non-polar residues are in the centre of the myoglobin molecule [0.5] 
and the polar residues are arrayed on the surface [0.8] aiding the solubility 
of myoglobin [2.4] and in now allowing myoglobin and indeed haemoglobin as it's 
since it's very r-, closely related to myoglobin to er [1.6] be in solution at 
relatively high concentration [3.9] so this of course is what we are really 
going to talk about today [0.9] myoglobin and haemoglobin [8.7] this then shows 
the arrangement [2.0] of the secondary structure wi-, in myoglobin which is 
predo-, predominantly alpha helical [0.4] into the globin fold so that would be 
its tertiary structure [1.6] and the tertiary structure [0.2] is essentially an 
arrangement of eight [0.5] alpha helices [0.4] in globins [0.2] er [0.3] 
labelled A to H this was A [0.5] B and C are behind here this is D [0.5] this 
is E [0.6] this is F [0.4] this is G [0.6] and this is H [2.3] you can also see 
that in myoglobin it has a prosthetic group [0.3] that's this red molecule here 
[2.2] and this prosthetic group [0.3] is essentially held in position [0.4] in 
a myoglobin in a [0.3] in a r-, in a a reasonable cleft or fold that helps 
protect that prosthetic group from oxidation [1.6] and m-, and the prosthetic 
group haem [0.5] of course is held in position [0.4] by two histidine residues 
[0.9] histidine [0.7] E-seven [0.2] and histidine F-eight so it's [0.4] the 
seventh residue in the [1.1] er [0.4] E helix and the eighth residue in the F 
helix [1.7] you can see that [0.6] the F-eight histidine appears to be quite 
close to the haem group [0.8] the [0.6] E [0.2] histidine appears a little bit 
further away [0.7] so the F- [0.3] eight histidine is called the proximal 
histidine [1.1] and the E-seven histidine is called the distal histidine [9.5] 
so what we are going to talk about today of course is the binding of oxygen to 
myoglobin and 
haemoglobin [1.9] we'll talk about the functions of myoglobin and haemoglobin 
[0.7] er [0.2] myoglobin acts as essentially as an oxygen store in muscle [1.9] 
and it you'll see that its structure is entirely consistent with its function 
[0.6] er whereas haemoglobin which is of course oxygen transport for 
transporting oxygen from the lungs to the tissues [0.4] we'll talk about the 
factors affecting oxygen binding [2.7] transport of carbon dioxide and P-H 
regulation [7.9] when we consider the binding of oxygen to haemoglobin and 
indeed myoglobin we'll [0.6] perhaps worth considering what atmospheric oxygen 
[0.5] er the [0.2] partial pressure axle [0.2] atmospheric oxygen is around 
about a hundred-and-fifty m-, millimetres of mercury or twenty [0.3] sometimes 
referred to as twenty pascals in other textbooks [1.7] a significant proportion 
of that [0.5] enters into the wet surface of the lungs providing of course 
those [0.6] er lung surfaces are wet if they're not for whatever reason [0.4] 
then you do not get efficient exchange between the atmospheric 
oxygen [0.9] and the lung mucosa [1.4] of the oxygen that dissolves into the [0.
5] lung mucosa [0.4] the majority of that is taken up [0.5] into the blood [0.
2] through exchange in the lungs [4.7] oxygen then is er the blood is then 
circulated oxygenated by this circulated in the tissues [0.6] and [0.4] a 
relatively small proportion [0.3] perhaps less certainly less than fifty per 
cent of [0.2] oxygenated haemoglobin [0.3] a relatively small proportion of the 
oxygen it carries is unloaded into the tissues [1.6] carbon dioxide is picked 
up from the o-, [0.3] from the active tissues and that's transported back via 
the blood [0.3] back to the lungs [0.7] and then back [0.3] er in exchange back 
into the [0.8] air that we breathe [1.5] so one of the [0.2] first factors 
that's going to affect [0.6] the [0.4] binding of oxygen to haemoglobin [0.4] 
is the efficient physiology here at [0.2] at the lung [1.3] er circulation 
interface [1.4] another more subtle perhaps [0.2] er notion is that it all 
relies on the fact that atmospheric oxygen is [0.7] what i said is up there [0.
6] and of course there are certain conditions when it's not for 
example altitude [1.7] and [0.4] that the lungs are er [0.3] er [0.2] 
functioning efficiently [0.2] that the circulation is functioning efficiently 
you can see that of the [0.4] oxygen that dissolves into the wet surface [0.3] 
the majority of it is taken up by the lung [0.2] by [0.2] by the blood in the 
lungs [1.2] so this is a fairly [0.3] this is working to almost its maximum 
efficiency n-, [0.2] at [0.2] at this point and anything [0.3] that affects 
that [0.4] well it ultimately affects [0.4] oxygenation of the tissues [4.4] so 
the rate at which you breathe [1.0] the so-called ventilation rate and the 
perfusion of the lungs I-E how much blood is passing through the lungs at any 
given time [0.7] er must be matched [0.4] that's called a ventilation and 
perfusion match [0.9] and the ratio must be approximately four litres of 
breathing per minute and five litres of blood per minute passing through the 
lungs giving you a ventilation [0.4] perfusion match of point-eight [2.2] 
anything that impears impairs breathing such as a a crushed chest [0.9] a 
deflated lung [0.9] chronic lung disorder [0.9] er [0.3] somebody [0.3] making 
the universal choking sign [0.7] er will affect [0.2] the amount of oxygen 
that's [0.2] that's breathed that they're that they're [0.2] able to [0.4] 
obtain [1.3] obviously if they have a problem with their blood flow [0.7] like 
they're bleeding from [0.5] a large artery in the leg [0.4] will ultimately 
affect [0.4] their oxygenation of their tissues but under those conditions i 
suggest you're more focused on the leg issue [1.0] er at least initially [0.2] 
and of course this relates to [0.4] the A B C of [0.2] first aid in many 
respects [0.3] airway breathing [0.2] circulation [2.6] and any [0.3] mismatch 
in ventilation or perfusion [0.2] will ultimately lower [0.4] the amount [0.3] 
of oxygen [0.2] in the arterial blood [1.2] so that reveals to you [0.2] that 
there's a problem with oxygen [0.2] oxygenation [4.7] so accepting that [0.6] 
the lungs are working properly and there's the right the correct concentration 
of atmospheric oxygen [0.5] we can then go back and and think about the binding 
of oxygen to haemoglobin and and myoglobin [1.5] this is the haem [1.1] er [0.
7] prosthetic group found in myoglobin and haemoglobin [0.6] it's made up of 
the the carbony 
bit it's called the protoporphyrin and in the middle there is [0.6] iron [1.1] 
the ferrous iron [0.4] that's iron two-plus [0.9] the as i said the hydrophobic 
fold [0.6] of myoglobin and haemoglobin protects oxidation of that iron [0.4] 
if that iron does become oxygenated er [0.2] oxidized it can no longer bind 
oxygen [1.4] so in that and in that case it's [0.2] that would be referred to 
as a met-myoglobin or a met-haemoglobin that's iron [0.5] in the [0.2] three-
plus oxidation state [1.9] the iron can make six coordination bonds it makes 
four [0.4] with nitrogens [0.3] that are in the pyrrole group [0.9] it makes 
one [0.2] with the pro-, with the nitrogen in the proximal [0.7] histidine [0.
6] and the last one [0.4] is for the binding of oxygen as i'll show you [0.3] 
and essentially this molecule [0.7] is planar [0.3] in isolation [5.7] so this 
then [0.5] er puts the haem then in context of those two histidines [2.1] er 
you can see here the proximal [0.5] er histidine providing the s-, the fifth 
coordination point for the iron [0.9] and oxygen is able to intercede between 
the [0.5] the distal [0.5] nitrogen in the histidine [0.4] 
and that provides the binding site for oxygen to [0.8] h-, [0.2] to haemoglobin 
[0.2] or indeed myoglobin [1.5] and in this case [0.2] in the presence of 
oxygen you can see that the [0.3] haem [0.6] remains planar [0.8] and and i'll 
explain why that's important in a little while [2.1] the other thing i want to 
point out is about er carbon monoxide [1.0] isolated haem [0.5] has a very 
strong affinity for carbon monoxide [0.3] much more [0.4] er er much stronger 
than it does for oxygen [0.7] but haem [0.3] in the presence of protein such as 
myoglobin or haemoglobin [0.4] there are r-, the [0.2] the differential between 
the affinities for carbon dioxide [0.5] and [0.6] oxygen is reduced such that 
it goes from twenty-five-thousand times difference in [0.3] isolated haem [0.4] 
to two-hundred times different [0.6] in the context of the protein so the 
protein plays an important role [0.4] in hopefully limiting the effects of 
carbon dioxide [1.1] the reason [0.6] that that's important is of course is 
firstly carbon dioxide is the single most [0.3] er single [0.4] biggest [0.4] 
metabolic poison [1.5] it's far more potent and there are far more deaths 
from carbon monoxide than there are for any other metabolic poisons that might 
[0.2] cyanide for example [5.7] and carbon monoxide [0.7] obviously actively 
competes [0.2] for oxygen binding sites [4.1] normally [0.3] er the er when 
once carbon monoxide is bound to haemoglobin or [0.4] to haemoglobin it will be 
referred to as carb-, carboxyhaemoglobin [1.7] and there is a small percentage 
of carboxyhaem-, haemoglobin in our blood normally [1.4] in smokers for example 
that percentage goes up to about fifteen per cent [1.5] and around thirty per 
cent it's a medical emergency [0.7] and around fifty per cent you're probably 
going to die [1.5] so carboxyhaemoglobin [0.4] is a significant [0.3] problem 
[1.0] because it's able to [0.2] effectively reduce [0.3] the oxygen ca-, 
carrying capacity [0.7] of blood [6.2] so now let's just think a little bit 
about this [2.9] planar haem molecule [10.9] this is the proximal histidine [0.
3] here's the planar haem molecule in the presence of oxygen [1.7] in this form 
[0.4] haemoglobin or myoglobin would be referred to as relaxed [1.7] when it 
becomes deoxygenated [0.6] the 
interaction between this nitrogen and the [0.4] iron in the haem group is so 
strong [0.4] that the haem tends to dome in [1.2] to that er [0.5] proximal 
histidine [0.7] in this case the [0.2] and that's deoxygenated form of 
haemoglobin it referred to as tense [1.5] so the binding of oxygen [0.4] to 
myoglobin or haemoglobin [0.3] essentially represents a tense [0.4] to relaxed 
transition [1.6] and that tense to relaxed [0.3] transition [0.4] can be 
transmitted through the molecule [0.3] because it is a shape change [7.2] so 
we've talked in general about the binding of oxygen to haem and everything so 
far i've told you is the case for as it is for [0.5] myoglobin as it is for 
haemoglobin [1.1] but of course haemoglobin is actually [0.2] a tetramer it has 
[0.2] four globins [0.2] so this is now a quarternary structure [1.7] the 
globin fold [0.8] of all four [0.3] of the [0.5] er [0.2] subunits in 
haemoglobin is shown [1.2] and you can see [0.5] the four haem groups [1.3] so 
oxygen is a er sorry so haemoglobin will bind four oxygens [0.4] as opposed to 
myoglobin which will only bind one [2.0] there you can see the 
doming in this particular haem group you can see the doming there [1.1] of the 
[0.4] haem [0.5] group [0.7] and of the i-, the iron being pulled into [0.3] 
the proximal histidine [3.4] adult haemoglobin there are there are three globin 
genes but there and there are multiple copies [0.8] in your D-N-A [0.3] er [0.
6] adult haemoglobin is predominantly so-called alpha-beta [0.4] haemoglobin [0.
2] you always express a little bit of delt-, delta haemoglobin [0.6] er during 
the first few months of life [0.6] you switch [0.5] from [0.2] the fetal 
haemoglobin [0.5] to these [0.2] adult forms [0.6] so obviously fetuses [0.2] 
fetal [0.3] expression is of [0.6] the H-B-F [0.2] and an adult's [0.3] a 
little bit of H-B-A-two [0.4] and H-B-A sometimes also referred to as H-B-A-one 
[8.4] so [2.6] now we understand a little bit more about the structure of 
haemoglobin and myoglobin how can we relate that to their functions [2.5] on 
the r-, on the left-hand side we have the s-, degree of saturation oxygen 
saturation of the proteins and [0.5] er partial pressure of oxygen [0.2] along 
the bottom [1.4] the green line [0.7] represents the binding of oxygen [0.7] to 
myoglobin [1.0] and it shows a 
simple hyperbolic relationship [1.7] entirely consistent [0.3] with a single 
binding site [2.8] and its responsiveness to [0.3] changes in oxygen pressure 
[0.8] are consistent with its role as a oxygen storage protein in muscle [2.9] 
myoglobin [0.2] is rapidly saturated over a relatively small concentra-, change 
in concentration [0.9] and will remain saturated [3.0] as a tissue a muscle's 
demand for oxygen increases [0.8] er [0.2] some oxygen can then be released [0.
3] from myoglobin [0.2] in order to support the metabolism [0.3] in active 
muscle [3.9] this is [0.8] er quite different to the curve that you see for 
haemoglobin [1.7] which is sigmoidal [0.6] in shape [0.8] consistent with [0.6] 
a multiple binding site [0.2] which we as we know is four [4.0] this [0.5] type 
of [0.5] er curve [0.7] a-, [0.7] reflects [0.3] what's called cooperative [0.
2] or politi-, [0.2] positi-, 
nm0442: allosteric binding [0.9] so oxygen [0.7] here [0.3] acts as an 
allosteric regulator of the binding of oxygen [0.5] to haemoglobin [1.0] the 
way to conceptualize that is this [1.4] here at the very [1.2] over a 
relatively wide concentration range at er here at the low end [0.3] of er 
haemoglobin's 
responsiveness to oxygen [0.5] it's very reluctant [0.3] to give up [0.3] its 
oxygen [1.7] as oxygen [0.5] er partial pressure increases [0.3] there's a 
rapid increase [0.8] in [0.2] haemoglobin's ability to bind oxygen [1.5] the 
only way you can s-, conceptualize that [0.2] is if the subunits [0.2] are 
cooperating [0.2] in their binding [0.6] of oxygen to haemoglobin [1.8] the 
probably the better way the best way to think of it is as they release [0.3] is 
as haemoglobin release oxygen [0.5] as it releases oxygen [0.2] it becomes 
progressively harder for haemoglobin to release further oxygen [3.6] and of 
course [0.7] here [0.2] fully saturated [0.7] the haem groups are relaxed [0.6] 
and here [0.5] as they're deoxygenated [0.8] they [0.5] become tense [5.4] so 
the binding of oxygen to haemoglobin er exhibits [0.4] positive allosterism it 
is cooperative [3.0] the cooperativity [0.3] essentially represents 
communication between the subunits [0.9] the er [0.2] quarternary structure i 
showed you showed that the subunits are in very close [0.3] proximity [0.2] and 
there are interaction faces between [0.3] all of the four subunits [0.7] so the 
binding of oxygen for example [0.2] here 
perhaps in the red subunit [0.5] can be transmitted [0.6] to [0.2] the other 
four subunits [0.2] so they're in close proximity [3.2] and that's because 
there's a [0.3] change of shape at the haem group and that can be transmitted 
[0.5] with a much larger change of shape [0.2] at the interactional face [4.7] 
this er [0.6] change in terms of [0.3] oxygenated and relaxed haemoglobin tends 
to close [0.3] a pocket [0.4] that form-, that can form in the middle [0.2] of 
the four subunits [0.7] in a deoxygenated form [0.5] this pocket tends to be [0.
5] a little bit more open [0.3] and we'll see the relevance of that [0.2] in a 
minute [7.0] so oxygen represents a positive allosteric regulator of the 
binding of oxygen to haemoglobin [0.3] and there are also some negative 
allosteric regulators of the binding of oxygen to haemoglobin [0.5] of course 
[0.5] i should remind you of course that myoglobin [0.2] is a monomer so there 
is no allosteric regulation [0.4] of the binding of oxygen to myoglobin [2.0] 
this i'm sure you'll recognize is a little bit of glycolysis [0.4] which i [0.
3] all medical students are always delighted 
to see glycolysis [1.5] [laughter] and er [0.2] in the erythrocytes there is a 
small side [0.7] er reaction [0.6] that's able to convert one of the 
intermediates of glycolysis to one-three-bisphosphoglycerate into two-three-
bisphosphoglycerate [0.8] it's discovered by this guy Rapoport and Luebering 
and it's called the Rapoport-Luebering shunt [0.2] not as somebody put in their 
exams last year the Freddie Ljungberg shunt [3.7] [laughter] two-three-
bisphosphoglycerate [0.2] is electronegative [3.0] and it is at very high 
concentration in erythrocytes [0.7] it's approximately equimolar with the 
concentration of haemoglobin [0.3] in erythrocytes [2.1] so you can see [1.2] 
glucose as it enters into glycolysis essentially [0.5] all the intermediates in 
glycolysis there's very little [0.3] of those [0.6] glucose enters into 
glycolysis in essentially [0.3] in erythrocytes of course is converted to 
lactate because they have no citric acid cycle no mitochondria and so on [0.9] 
the only other [0.3] intermediate [1.7] 
is two-three-bisphosphoglycerate [0.3] formed by the [0.7] the shunt [4.2] and 
the role of two-three-bisphosphoglycerate is effecti-, is e-, to effectively 
lower the affinity [0.6] of haemoglobin for oxygen [11.6] this is a little bit 
schematic in the absence of [0.4] er bisphosphoglycerate this this curve 
actually would shift be shifted quite [0.2] quite a little way to the left [0.
3] in relation [0.4] to the normal [0.5] haemoglobin [0.4] in erythrocytes [3.
0] so in the absence of er in the absence of two-three-bisphosphoglycerate [0.
3] haemoglobin would be quite reluctant to give up its oxygen at all [1.0] 
obviously as this would be a problem [0.3] for the delivery of oxygen [0.3] to 
tissues [0.4] and ov-, and clearly we have adapted [0.2] to use two-three-bo 
bisphosphoglycerate [0.3] to enable us to moderate [0.2] the release [0.2] of 
oxygen [0.5] er in the active tissues [2.2] the two-three-bisphosphoglycerate 
is [0.2] is [0.2] is [0.9] binding site is found in the centre [1.4] of the [0.
6] haemoglobin [0.8] er tetramer [0.5] it's [0.2] predominantly formed by 
interactions with [0.2] some alpha chain interactions and predominantly beta 
chain [0.3] interactions [0.6] er and these 
are positive residues electropositive residues like lysine and arginine and 
histidine [2.7] two-three-B-P-G combined to the [0.6] deoxygenated form of 
haemoglobin helps stabilize [0.6] er the dexoygenated form [0.2] and helps 
release oxygen [0.5] into the tissues [7.8] a clear demonstration of the 
importance of two-three-bisphosphoglycerate is the fact that there is no two-
three-bisphosphoglycerate binding site in fetal haemoglobin [1.2] so the gamma 
chain [0.4] in er fetal haemoglobin does not have those electropos-, positive 
residues [0.2] so that binding site isn't present [1.5] this means that fetal 
haemoglobin has a higher affinity [0.6] er for oxygen than does the maternal [0.
4] haemoglobin [1.2] and that ensures that oxygen will flow from maternal 
haemoglobin [0.2] to fetal haemoglobin [4.1] one can imagine other scenarios 
where the level of two-three-bisphosphoglycerate [0.4] would be moderated [0.2] 
in order to increase the supply [0.4] of oxygen [0.8] to the tissues [0.3] for 
example at altitude [0.3] one of the adaptions to altitude [0.2] is to increase 
[0.4] your levels of 
two-three-bisphosphoglycerate [0.2] and that helps unload [0.3] oxygen in the 
tissues [0.8] chronic lung disease [0.3] is another case in which you see [0.4] 
increases [0.2] in two-three-bisphosphoglycerate concentration [0.4] as the 
body's attempting to compensate [0.2] for poor oxygenation [0.4] and to deliver 
as much oxygen as possibly can [0.6] to the tissues [1.4] this has to be a 
temporary solution and in people with chronic lung disease it [0.2] it itself 
[0.2] perpetuates the problem [1.0] since [0.3] they increase their two-three-
bisphosphoglycerate and it becomes progressively harder then to reoxygenate 
your haemoglobin in the lungs [1.5] does everybody understand the role of two-
three-bisphosphoglycerate [1.7] is there any divers in the room [2.0] any 
divers scuba people come on there must be one or two [0.2] you [0.8] if i give 
you the choice [0.7] imaginary choice [0.6] two-three-bisphosphoglycerate [0.2] 
small white powder [1.1] or air [0.9] and you're going diving [0.3] which are 
you going to take [1.7] 
sf0443: 
it's obviously a trick question isn't it 
nm0442: no [0.3] it's not a trick question [laughter] [2.7] 
sf0443: [0.4] 
nm0442: the air [0.2] you're going to take the air [0.3] 
sf0443: yeah [0.4] 
nm0442: two-three-bisphosphoglycerate is not an oxygen substitute [1.3] okay [0.
2] one of the favourite answers of medical students [1.1] think of the diver 
give him the option [0.3] of the white powder or the air [0.3] and see which 
one he takes [0.4] nobody takes the two-three-bisphosphoglycerate [0.4] it is a 
negative [0.3] allosteric regulator of the binding [0.3] of oxygen to 
haemoglobin [0.4] it is not [0.2] an oxygen substitute [1.2] good [4.3] there 
are two other negative allosteric regulators of the binding of oxygen to 
haemoglobin [2.6] they are hydrogen [0.2] and carbon dioxide [2.0] and as you 
can see here a d-, a decrease in P-H [0.5] effectively reduces [0.8] the 
affinity of [0.5] haemoglobin for oxygen [2.4] and that [0.5] helps [0.6] 
unload [0.2] oxygen [0.4] in active tissue [0.5] since in 
active tissue [0.3] the concentration of hydrogen [0.2] and carbon dioxide is 
high [4.1] both these molecules do so [1.2] by interfering [0.9] with cross-
bridging that interaction between [0.2] haemoglobin subunits [0.7] carbon 
dioxide can interfere with cross-bridging [0.5] firstly because it actually of 
course can [0.7] in solution [0.2] can increase the hydrogen ion concentration 
[0.3] as we'll [0.2] see in a minute [0.8] and secondly [0.4] because i-, [0.4] 
it can bind to haemoglobin [0.5] it it doesn't bind [0.7] at [0.3] the ion [1.
6] so a certain amount of carbon dioxide is transported by haemoglobin [0.6] 
but is transported covalently [0.5] attached to free amine groups [2.1] so 
that's called carbaminohaemoglobin [1.4] and that's different from 
carboxyhaemoglobin which is carrying carbon monoxide [0.8] at the ion [3.9] so 
carbaminohaemoglobin carrying carbon dioxide obviously [0.2] interferes with 
cross-bridging interferes with oxygen binding [0.5] and hydrogen ions interfere 
with [0.3] cross-bridging [0.2] communication between subunits [0.4] and can 
lower the affinity [0.5] of haemoglobin for oxygen [2.7] so let's just consider 
[0.6] a 
little bit the transport of carbon dioxide [4.8] carbon dioxide [0.3] and water 
can be combined in the erythrocyte using the a-, enzyme carbonic anhydrogena-, 
[0.5] carbonic anhydrase [0.2] to produce carbonic acid [0.3] which rapidly 
diassociates to form a carbonate ion [0.5] and hydrogen [1.6] the majority of 
carbon dioxide produced in tissues is transported [0.6] in the form of 
carbonate [1.2] once it's made in the erythrocyte it passes out through the 
erythrocyte in a specific transporter and [0.5] i-, [0.2] er present in the [0.
6] plasma [1.7] a relatively small proportion is transported back [0.3] 
actually covalently linked to [0.4] er [0.5] haemoglobin and [0.4] 
interestingly of course the covalent link [0.2] of carbon dioxide to [0.3] 
haemoglobin [0.3] also [0.7] lowers [0.9] D-P-H raises the hydrogen ion 
concentration [4.6] just to remind you of course [0.2] carbon dioxide protons 
all their equivalents are of course the major metabolic end points [0.4] when i 
say equivalents i'm thinking about [0.8] lactate lactate or ketones what have 
you [21.0] so we come back we f-, we return 
to the lungs and consider now [1.1] the binding of oxygen to haemoglobin in the 
lungs [0.4] here i've represented haemoglobin [0.5] carrying a proton [0.8] 
which is released as oxygen binds [0.8] this proton [1.5] can drive the 
carbonate equilibrium [0.5] to the left [1.1] pushing carbonate back to 
carbonic acid and causing the [0.5] the [0.2] evolution of carbon dioxide in 
the lungs [1.4] oxygenation of this species is reducing the concentration of 
this species in the blood [0.4] and that helps [0.8] drive this equilibrium [0.
5] to the left [0.5] to release [0.2] the bound carbon dioxide [0.4] that's 
bound to haemoglobin [1.9] so then the lungs of course because oxygen 
concentration is high [0.4] favours [0.5] oxygenation [0.5] of haemoglobin [3.
8] so that's shown on the left [0.7] sort of schematically the erythrocyte [0.
4] the alveolar surface [1.3] incoming oxygen [0.4] the shift in the hydrogen 
ions so-called isohydride shift [1.7] and the driving of carbon dioxide out of 
[1.0] the erythrocytes [0.4] and [0.2] into [0.4] the alveoli [0.9] and into [0.
2] the air we breathe out [0.6] and exactly the opposite is true [1.6] in 
active tissues in active tissues [0.4] carbon 
dioxide and hydrogen are are [0.2] concentrations are high [0.9] they're taken 
into the erythrocyte [0.3] converted to the carbonate ion [1.0] the carbonate 
ion is transported out by [0.3] er er [0.4] a chloride carbonate antiporter 
it's called band three in erythrocytes you'll learn a bit more about 
transporters in the next couple of weeks i think [1.5] there's the isohydride 
shift [0.3] that helps to drive [0.2] oxygen off [0.4] haemoglobin [0.5] and 
drive it into [0.6] the tissues where it's needed [4.1] obviously all this [0.
2] er [0.3] movement of hydrogen ions essentially means that [0.3] the P-H [0.
6] in blood has to be very tightly regulated [1.2] normal [0.4] physiological 
pa-, P-H is in a very narrow range [1.2] and any factors that [0.4] t-, er [0.
5] take the [0.3] normal physiological P-H outside this range can be dager-, 
dangerous indeed deadly [1.4] you ca-, if you would look up [0.2] er you can 
look up things like er acidosis [0.3] in newborn children or er [0.2] er 
premature children [0.5] and [0.3] you can see the you'll be able to read about 
the effects [0.2] of acido-, that acidosis has [0.3] on both the physiology [0.
3] er the long term [0.3] development 
of children their mental acuity and so on [1.3] so regulating P-H is very very 
important [2.2] and of course the main system that does it is the one we've 
just described it's the bicarbonate buffering system this represents about 
seventy per cent [0.2] of the buffering capacity of blood [1.4] phosphate also 
can be involved in [0.8] er buffering and indeed of course the various proteins 
[0.5] can do a little bit of buffering [2.0] but of course this system is open 
[0.3] it's open at this end because it's open in the lungs the carbon dioxide 
[0.6] the equilibrium's open at that end [0.4] the er equilibrium's open at the 
proton end because protons are the major metabolic [0.3] end points [0.2] as 
indeed is carbon dioxide [3.0] so we can relate the control of blood [0.5] to 
the way in which we are respiring [4.4] if we're hyperventilating perhaps 
panicking about the molecules exam [2.5] [laughter] then we're breathing deeply 
and rapidly [1.8] that will force [0.3] carbon dioxide out of the lungs [0.7] 
draw this equilibrium [0.5] to the left pulling protons 
in [0.7] and the P-H of the blood will essentially [0.6] become more alkali [3.
2] so in-, [1.8] yeah [0.8] so it [0.4] so hyperventilation is [0.3] towards 
the alkali [0.8] poor [0.4] ventilation [0.3] chronic [0.3] obstructive 
pulmonary disease [0.5] is going to keep carbon dioxide deep in the lungs and 
force the equilibrium [0.3] to the left [0.6] and the hydrogen ion 
concentration will increase [1.2] so hyperventi-, hypoventilation [0.4] is 
going to be giving you [0.3] acidosis [0.6] and hyperventilation [0.5] is 
giving you [0.2] alkalosis [3.9] this of course [1.1] the realization here is 
of course that the [0.5] the lungs represent a very major control [0.2] of P-H 
[3.9] so here's respiratory alkalosis [0.4] caused by hyperventilation [0.2] 
simple treatment [0.3] rebreathe or administer carbon dioxide [3.4] conversely 
re-, respiratory acidosis caused by inadequate breathing [0.2] unable to [0.2] 
exchange the carbon dioxide in the lungs [1.4] er [0.9] have to administer more 
buffering [1.1] probably I-V [4.1] so the important point here [1.9] is that [0.
9] because those equilibria are open [0.4] at 
either end [2.3] er [0.4] respiratory [0.2] changes in P-H [0.3] are related to 
metabolic changes in P-H [5.7] so there are various much more common conditions 
that [0.2] for example [0.5] uncontrolled diabetes diarrhoea [0.2] overdose of 
aspirin [1.6] where or indeed [0.2] prolonged heavy exercise [0.3] hec-, 
exercise where you become metabolically acidotic you produce a lot of acid 
equivalents [1.9] and that interferes [0.2] with that carbonate buffering 
system [0.8] and it overloads it at the right-hand end [1.8] and so you go into 
deep [0.8] rapid breathing you hyperventilate [0.5] to blow off carbon dioxide 
[0.9] what you're trying to do is pull hydrogen ions in [0.5] from the 
metabolic [0.7] acidosis [0.7] and blow carbon dioxide off [0.7] so respiratory 
alkalosis is linked to metabolic acidosis [0.7] and therefore [0.8] a m-, [0.2] 
a respiratory alkalosis [0.2] although is a condition itself [0.2] may be 
caused [0.9] by metabolic acidosis [1.2] similarly the opposite is true if 
you're prolonged vomiting you lose a lot of hydrogen ions from the stomach you 
become [0.6] er and you go into metabolic alkalosis [0.4] then [0.2] your 
breathing becomes 
shallow and infrequent [0.3] as the [0.5] body attempts to compensate for that 
[0.6] by holding on to the carbon dioxide forcing the equilibria to the right 
[0.5] and increasing the hydrogen ion concentration [0.3] to combat [0.4] the 
alkalosis in the blood [2.7] okay [1.4] so we've talked about the transport of 
oxygen we've talked about the transport of car-, [0.2] carbon dioxide and we've 
even talked a little bit about respiratory control of P-H [0.5] i've talked 
about [0.4] acidosis and alkalosis [0.3] in relation to the [0.7] lung [0.4] 
the other major organ which i'm not going to talk about that controls P-H is of 
course the kidney [5.4] so [0.5] clinical correlations [0.7] other clinical 
correlations perhaps [3.1] haemoglobin can become glycosylated in blood this is 
a spontaneous [0.2] er [0.2] reaction between haemoglobin and glucose [0.5] and 
in [0.3] uncontrolled diabetes [0.3] when [0.3] glucose levels are elevated in 
blood [0.4] glycated haemoglobin [0.3] acts as a measure [0.4] over the 
previous [0.7] three [0.3] three or four months [0.5] er [0.4] acts as a 
measure [0.4] of the level of control [1.0] of diabetes [0.3] for example if er 
a diabetic 
hasn't been [0.3] following the insulin regime [0.3] their glucose 
concentration will have been fluctuating wildly [0.6] in their blood [0.6] and 
gluc-, and the [1.2] glycosylated haemoglobin acts as a marker for that [1.6] 
we've already talked about the role of two-three-bisphosphoglycerate [0.2] 
stored blood of course [0.4] the two-three bisphosphoglycerate rapidly [0.3] er 
degrades [0.4] so it nus-, needs to be added to stored blood if it's going to 
be transfused and we've also talked about the physiological [0.7] er [0.2] 
conditions that may alter the level of two-three-bisphosphoglycerate [1.4] what 
we haven't talked about at all [0.4] are haemoglobinopathies [0.5] such as 
sickle cell and the related thalassemias they are relatively rare and there are 
many of them [0.9] they all relate to either alterations in the globin 
structure or indeed [0.4] er a loss [0.4] of expression of a globin gene [0.3] 
thalassemias p-, vary in their [0.4] er severity from relatively mild [0.6] to 
relatively severe [0.9] er and this would be an area i suggest you have a brief 
look at if you get the 
time [2.1] right [1.7] hello oh [0.9] good [0.7] well that [1.5] has [0.3] 
taken nearly [0.2] well just over half the lecture i thought we'd just have a 
little break now [0.7] and do something a little bit different 
sf0444: [9.6] so obviously they just brought somebody in unconscious [29.8] 
sf0444: and Malucci being a bigot just ask first and then he completely ignores 
what he said [21.9] 
sf0444: heart attack [23.4] 
sf0444: so Malucci's really caught up in the [0.3] he's [0.3] [18.1] 
sf0444: and now he's just trying to pressure the doctor into making his 
decision [26.4] 
sf0444: they've just lost the patient [23.8] 
sf0444: now in the scene [44.5] 
sf0444: and then he's still stuck on the fact that it's drug-related [0.2] 
though [0.2] [11.5] 
sf0444: so they've started giving a clot-buster to somebody who's completely 
bleeding out so now he has no [7.1] and he's haemorrhaging [0.6] [8.7] and 
that's the i'm in big shit look [2.1] 
nm0442: 
round of applause for namex there [1.1] well done [5.9] ooh get rid of that [4.
3] okay [2.3] so the classic differential [0.5] on M-I [0.8] is dissection [0.
9] the aorta the aorta splitting [0.7] and if you misdiagnose your M-I [0.5] 
you give a clot-buster and they bleed into the chest because they're dissecting 
and it was the clot that was holding them together [1.6] and [0.9] as er [0.3] 
Carter the unstoppable sex machine spotted [1.5] [laughter] er this guy's a 
Marfan [1.0] and a Marfan [0.6] is er a collagen or it's actually a collagen-
related disease [0.2] he has Marfan's syndrome [0.7] and Marfan's syndrome [0.
3] is a defect in collagen [0.9] and frequently [0.8] er pathologically [0.4] 
these people suffer from vascular problems [0.3] and various other [0.3] 
presentations of a a collagen disease [0.4] so [0.4] what we're going to talk 
about now [0.5] is collagen [2.0] so in everything i've kind of told you about 
haemoglobin and about helices [0.3] when it comes to collagen you 
begin to throw all these things out of the window [1.9] the first thing is that 
it has er essentially a repeating structure of of essentially three amino acids 
it's a gly-X-Y as it says there gly-X-Y motif [0.4] and X and Y are either 
proline or hydroxyproline lysine or hydroxylysine mainly [1.8] er [0.5] it's 
found in of course [0.4] tendons cartilage [0.5] bones on the surface on the 
articular surface of bones even in the eye [1.8] er the micrograph there just 
gives you an idea of the structure of collagen fibres and we see this kite [0.
2] quite characteristic [0.4] er [0.4] banded pattern that's seen in obviously 
only in fibres [0.4] and then at the end there this cross section you can see 
how they represent bu-, fibres of [0.3] er bundles of fibres bundled together 
[4.8] there are [0.4] it says at least ten there are about [0.2] thirty [0.9] 
different types of collagen [1.6] some form fibrils [1.0] some [0.2] s-, form 
mal-, small fibrils called microfibrils [0.7] some are associated with fibrils 
and are a little bit fibrillar-like [0.5] but also have [0.4] interruptions in 
their fibrillar 
structure [0.3] and some [0.2] just form network [0.2] meshworks [1.6] so there 
are fibrillar types [0.9] microfibrillar types [0.3] non-fibrillar types and [0.
3] fibrillar associated collagens [0.2] with interrupted triple helix [0.7] 
facit [1.2] okay [0.2] for those of you are from Essex that's not [0.2] fuck it 
[5.8] [laughter] okay [0.8] and the structure is completely different [0.4] 
it's a left-handed helix [2.9] it is a very tight turning helix and it's it's 
left-handed [0.4] and tight turning because of the residues in there [0.3] 
proline helps [0.4] er the tight turn [0.6] as does hydroxyproline [1.1] 
glycine has [0.2] virtually no [0.3] side chain [0.2] so that allows [0.2] the 
turn to be very tight [3.5] and a single collagen [0.4] left-handed helix [0.4] 
is wound with two other left-handed helices [1.4] to form a right-handed 
helices [0.3] er a coiled coil [0.5] and coiled coils of course [0.2] 
structurally [0.2] are very strong [1.0] that's not to say that [0.4] er [1.3] 
any strong protein structure has to be helices because there are plenty of 
examples of [0.2] strong protein structures that are beta sheet [0.2] and silk 
fibroid [0.2] is a very good example of that [0.5] 
but [0.2] nevertheless coiled coiled [0.3] type structures [0.2] are 
structurally [0.5] very strong [2.0] so i'm just going to briefly [0.5] review 
[0.7] the biosynthesis and post-translation of collagen and then we're going to 
go through it in a little more detail in subsequent slides [0.2] but basically 
[1.7] of course the M-R-N-A is translated and it is [0.3] both translated and 
secreted [0.4] into the E-R [2.7] in the E-R [0.6] the [0.2] lysines and 
prolines become hydroxylated [0.9] by specific hydroxylases [3.9] some of the 
hydroxylated residues will subsequently become [0.2] glycosylated [0.7] so 
there's O-link glycosylation on those hydroxylated residues [0.8] others will 
be involved [0.4] in promoting hydrogen bonding and it [0.3] the hydroxy 
residues are involved in hydrogen bonding [0.2] and also indeed in cross-
linking [0.2] as we'll see further along [2.1] there's also some end-linked 
glycosylation [1.7] of of collagen [1.7] and the ends of the collagen molecule 
are [0.4] disulphide bridged to form a sort of globular structure [2.0] so 
there are several post-translational modifications that occur [0.3] in the 
E-R [0.8] the hydroxylation the glycosylation [0.4] and the formation of 
disulphide bonds [1.6] three [1.5] collagen helices are then wound together [1.
0] and this winding [0.5] involves [0.5] the [0.7] er r-, arraying these 
collage-, these s-, sorry globular [0.7] gr-, er [1.0] modules at the end [0.5] 
of the collagen fibre [0.5] they help bring the three collagen fibres together 
and promote the winding of three collagen fibres [1.7] glycosylation [0.2] in 
amongst the [0.5] wound areas helps er interrupt the helices hence [0.3] 
interrupted [0.4] triple helix [1.9] go-, so glycosylation plays an important 
role in [0.3] er interrupting the triple helix [0.3] it also plays a role [0.3] 
in maintaining the solubility [0.2] of collagen [0.4] so it's a [0.4] the er 
carbohydrate molecules help [0.3] attract the water [2.0] this then is secreted 
[1.6] out of the cell and the secretion of such a large molecule is not an 
insignificant task [2.2] the globular [0.3] portions will be removed [1.4] 
leaving the mature fibre [0.5] with a degree of [0.3] interruption in the 
triple helix or not [0.5] and some of the re-, residual [0.5] hydroxyl groups 
particularly the ones at 
the ends [0.4] of the mature fibre [0.3] are involved in cross-linking this 
fibre [0.3] to another fibre [0.4] and that cross-linking [0.5] er [0.3] is 
evidenced by the banded pattern [0.2] that we see [0.4] in collagen in 
fibrillar collagens [2.2] so in a little more detail then [0.9] er this [0.2] 
exe-, example for proline [1.9] there are specific [0.4] er [1.9] hydroxylases 
in the er [2.0] E-R [0.7] and they're vitamin C requiring [3.8] the absence of 
vitamin C [0.5] er [1.3] results in improper hydroxylation [0.4] of [0.3] 
proline [0.2] and lysine [1.4] and vitamin C deficiency is of course scurvy [1.
5] i quite like this little description of scurvy from [0.3] er Jacques Cartier 
who er [0.3] discovered Canada [0.3] fifteen-hundred like the last bi-, bit the 
best [0.3] their mouth became stinking [0.4] their gums so rotten [0.4] that 
all the flesh did fall off even to the roots of the teeth [0.2] teeth [0.2] 
which did also almost all fall out [0.7] course in retrospect he didn't know [0.
2] that they were on the Atkins diet [2.0] [laughter] [laughter] [2.2] so [0.3] 
first key point in er collagen biosynthesis [0.4] you need vitamin C [3.6] the 
sp-, the the 
residues [0.8] glycine hydroxyproline and proline [0.2] permit the association 
of the three chai-, the three chains together and they can be [0.2] become 
intimately [0.2] interwoven [0.5] here [0.6] one of the residues [0.6] er has 
been mutated [0.8] in silico in the computer [0.3] to an alanine [0.7] and that 
drives the chain apart in this [0.3] area [0.6] so a simple [0.5] mutation [0.
4] in collagen [0.3] can drive [0.3] the chains apart [1.2] and weaken the 
overall collagen structure [1.7] this is of course the basis [0.3] of 
osteogenesis imperfecta [1.0] where there is a mutation [0.4] of a glycine in s-
, [0.3] mi-, most of the time it's to a cysteine it occurs in [0.3] one of the 
major coloni-, [0.3] collagen types [2.2] there are sev-, because there are [0.
3] three [0.7] three collagen genes there are [0.8] multiple variations [0.3] 
into the presentation of osteogenesis imperfecta [2.1] normally they of course 
will have [0.2] brittle bones as the name suggests osteogenesis is [0.4] 
generation of bones imperfecta [0.3] imperfect [0.6] it is relatively rare [1.
7] and in certain cases [0.2] can be absolutely lethal [1.6] give you an idea 
of what sort of X-ray of what a p-, a baby with 
osteogenesis imperfecta looks like you can see these [0.6] multiple fractures 
here [1.2] the [0.2] sort of [0.9] thickening and the thinneni-, thinning of 
the bone these you can't see the ribs very well but the ribs are v-, quite 
characteristically in this sort of [0.4] er [0.8] this sort of er [0.2] 
appearance on X-ray [1.9] so it's quite a severe disease [0.2] it's also some s-
, [0.2] frequently collagen disor-, disorders can be picked up [0.6] in the 
whites of the eye the so-called sclera of the eye they have a s-, slightly blue 
or greyish tinge [0.3] because of the collagen [0.4] that's in the er the 
whites of the eye [0.6] and in er [0.2] patients with osteogenesis imperfecta 
[0.5] there's less collagen in the eye [0.3] and a pigment from behind the e-, 
the eye shows through [0.3] and so they have an apparent blue tinge [0.4] to 
the sclera [4.6] the [0.2] part of the [0.2] structural integrity of collagen 
is through hydrogen bonding between those hydroxyprolines [0.4] er [0.2] and er 
[0.2] glycines and proline residues [0.3] that gives [0.8] cross-chain or [0.3] 
interchain [0.4] hydrogen bonding it helps stabilize the hae-, helix and [0.2] 
contribute 
to the mechanical strength [0.3] that's seen in [1.0] collagenous [0.4] er 
tissues like tendon [6.9] here we can see a little more detail on the the role 
of this globular domain [0.6] it helps bring the three chains together allows 
them to twist together to form the [1.2] mature [0.5] tropocollagen and then 
these are removed [0.4] in the extracellular space [0.7] by an enzyme called 
procollagen peptidase [2.7] a deficiency in procollagen peptidase is 
characterized by [0.3] a syndrome called Ehlers syndrome Ehlers Danlos syndrome 
[2.3] heard a little bit about this in the genetics lecture because Ehlers' 
very complex [0.2] can have complex inheritance [0.7] it's quite char-, 
characteristic [0.3] hypermobile [0.3] joints and very stretchy skin 
nm0442: er [0.7] and [0.9] like many of these [0.3] er collagen and collagen-
related diseases the prognosis may be shortened [0.5] because of vascular 
complications in the heart [0.3] or in the major vessels [8.9] once the mature 
collagen [0.3] fibre has been secreted into the extras-, extracellular space 
it's cross-linked [0.2] it's cross-linked at the en-, [0.4] at 
the ends here [1.8] free hydroxyls from l-, er [0.2] free hydroxyls [0.2] free 
hydroxylysines [0.2] or indeed lysines [0.2] are covalently linked [0.3] across 
[0.8] these [0.6] triple helices [3.5] this gives you an idea actually this is 
a lysine cross link [0.6] to form a so-called shift base [2.4] you don't really 
[0.3] you just need to know that that's a covalent link you don't really need 
to worry about the f-, the [0.6] fan-, fascinating structure of a shift base [0.
5] er [0.7] nevertheless [0.6] there is another disease associated with the [0.
6] improper cross-linking of collagen and that's called lathyrism [2.4] 
inhibition of lysyl oxidase the cro-, the collagen cross-linking enzyme [1.3] 
by found [0.4] this compound's found in sweet pea so although sweet pea of 
course is a [0.5] very good source of vitamin C [0.2] it's not necessarily the 
best cure for scurvy [0.4] because actually what you do is you inhibit the 
lysyl oxidase [1.2] okay and again [2.2] a collagen disease where dislocations 
of the joints [0.2] and vascular problems [1.7] are associated with the disease 
[2.7] all of those diseases represent loss [0.3] of function [1.7] 
but gain of function or [0.3] deposition of collagen [0.2] can be le-, [0.2] 
can be equally as dangerous [0.6] it's referred to medically as fibrosis [2.9] 
in exa-, for example in a medical student liver [0.2] being constantly abused 
by alcohol scarred [0.6] collagen is busily being deposited in [0.2] that 
gentleman up there who's [0.2] [laughter] [0.4] busy partying every night [0.6] 
and er [1.9] that can result in impaired liver function [0.9] similarly in the 
heart fibrosis of the heart tissue is going to result in severe [0.5] er 
reduction in the efficiency of the heart in stroke volume and so on [1.3] and 
that and that er again [1.4] serious er complication [0.6] lung fibrosis is 
quite interesting and and of course [0.7] lung fibrosis is going to 
dramatically reduce the oxygen uptake [0.5] the oxygen uptake ability of the 
lungs [0.4] and lung fibrosis is frequently caused [0.6] er in [0.3] it's 
frequently found in patients in long term stay in hospital [1.7] and can be 
induced [0.3] indeed quite rapidly by certain drug treatments as well so you 
can [0.2] you can treat patients with certain drugs and 
all of a sudden [0.3] you induce lung fun-, fibrosis and it's a very serious 
problem [1.2] so both loss of function and gain of function of collagen [0.4] 
are serious [0.3] medical issues [5.3] in the main we've talked about these 
fibrillar collagens and the er the er notion that they're [0.9] they're of 
course involved in ligaments tendons in the architecture of joints [0.5] er 
that they are [0.7] in in [0.2] in those cases they're complex molecules they 
contain fibrillar collagens microfibrils they contain collagens that are is-, 
just [0.2] there to be associated [0.2] with the fibril [1.4] other collagens 
[0.3] and du-, generally these collagens will be much more heavily glycosylated 
[0.2] form branch structures [0.5] they form [0.6] meshworks [0.2] that are 
involved in the formation of basement membranes which [0.2] endothelial layers 
[0.4] grow on the when on which fibroblast [0.6] layers will grow [2.9] right 
well should just say as well of course in in this case the extracellular matrix 
is not just collagen it's associated with a lot of other proteins proteoglycans 
[0.4] er glycoproteins [0.3] and the 
various elastins [0.4] and [1.5] it's the elastin gene [0.5] which there's only 
one [0.6] er [0.2] er gene er one elastin gene [0.2] that's mutated in Marfan 
[2.5] it's similar to collagen it has this glycine and proline [0.7] rich 
sequence [1.0] has er [0.4] more valine in it [0.3] it's essentially very 
hydrophobic [1.6] it [0.2] it er [0.3] it's le-, much less post-translationally 
modified than is collagen [0.2] it has very little secondary struc-, 
recognisable secondary structure perhaps that's consistent with its er more 
elastic properties [0.9] it is cross-linked in the same way as collagen is by 
the lysyl oxidase [2.6] and it's mutations in that fibrillin gene [0.4] that 
make up elastin fibres [0.2] that are responsible [0.4] for the Marfan [0.5] 
syndrome [3.2] and quite characteristically the Marfans are tall [0.6] they 
have er [0.2] long limbs [0.2] arachnodactyly which is spidery long fingers [0.
6] and the thing that er [0.4] alerted [0.4] Carter was the [0.2] pec-, pectus 
excavatum which essentially means a slightly sunken chest [5.4] so [1.5] in 
just about an hour we have reviewed protein structure [1.1] we've talked about 
the 
binding regulation of the binding of oxygen to haemoglobin and myoglobin and 
we've even [0.3] watched telly and done the collagen diseases [0.4] you will 
notice at the end of your lecture handout [0.4] that there are a few sli-, 
there are a few slides i've included about er [0.3] the molecular basis [0.6] 
of the contraction of muscle [0.5] something that we [0.2] don't have time to 
cover [0.8] in this series and something i suggest you use your hour [0.8] now 
to have a little brief look at and familiarize yourself with [0.3] in 
particular [0.8] the basic [0.4] er [0.5] apparatus that's involved in skeletal 
[1.1] smooth and cardiac muscle that regulates the contraction [0.6] and even a 
little bit on how to recognize what a skeletal muscle cell looks like [0.3] 
compared to a smooth muscle cell [0.5] compared to a cardiac muscle [1.0] okay 
[0.9] so we're done for the [0.3] the groups that have got to go i suggest you 
go if there's anybody who wants to come and ask me something come down when [0.
3] when [0.2] the first group have [0.3] got away