L22- Haemoglobin and myoglobin Flashcards
both haemoglobin and myoglobin have functions in
oxygen transport
why does oxygen need a transporter to get to tissue
veyr insoluble
oxygen binds to …….. and is transported fromt he lungs to the tissue
Fe group of Hb
what else can Hb transport back from the tissue in the lungs
carbon dioxide and H+ ions
which group in haemoglobin and myoglobin does oxygen bind to
haem group
Haem group structure
- protoprophyrin ring , with Fe in the centre surrounded by 4 Nitrogen atoms
Fe2+ in the centre of haem can make
2 additional bonds to oxygen- one either side of the plane
- oxygen binds above and below the ring
function of myoglobin
faciliates oxygen diffusion throguh muscle tissue
- local reserve of oxygen during intense exercise
how many polypeptide chains in myoglobin and how many aa
one- 153 aa
- tertiary structure
what sort of protein is myoglobin
globular protein
secodnary sturcture of myoglobin
75% alpha helical
where is haem prostetic group found in myoglobin
in the middle- covalently linked to Fe
a protein is anything larger than
100 amino acids
function of haemoglobin
contained in RBCs, which efficiently carries oxygen fromt he lungs tot he tissues of the body for respiration
also has a role int ransporting carbond dioxe and hydrogen ions back to the lungs
haemoglobin structure: how many subunits
4
- 2 different types of polypeptide chain
e. g. alpha2beta 2
haemoglobin structure is an example of
quaternary structure
each subunit of hb contains
essential haemo prostethic group
conformation of each subunit (polypeptide chain) in Hb is very similar to that of
myoglin - similar aa sequence
oxygen biudnding to haem in myoglobin
Deoxymyoglobin –> myoglobin
oxygen bidnding to myoglobin show a ….
hyperbolic dependence on oxygen concentration
features of oxygen bidning to myoglobin
Process is reversible
Constant affinity to oxygen
Most of the O2 is released in active muscle
P50
partial pressure giving 50% saturation
oxygen dissocaition curve for myoglobin vs haemoglobin
Myoglobin has a much higher affinity to oxygen than haemoglobin
why are the oxygen dissociation curves for myoglobin and haemoglobin different
Haemoglobin doesn’t have a constant affinity to oxygen – T –> R state
what structureal changes happen to Hb on binding to oxygen
deoxyhaemoglbin can exist in low affinity T state or high affinity R state
Oxygen binding promotes stabilisation of the R state (i.e. why the graph has a low gradient at first)
T state
low affinity
R state
high affinity
why is the oxyegn bidnding curve for haemoglobin sigmoidal instead of hyperbolic?
The binding of one oxygen molecule causes a conformational change in one subunit which promotes the binding of subsequent molecules
(e.g. T–> R state)
The binding of one oxygen molecule causes a conformational change in one subunit which promotes the binding of subsequent molecules also known as
Cooperative binding of oxygen to Hb
why is the sigmoidal curve of Hb important
means O2 can be efficiently carried from the lungs to the tissue
More sensitive to small difference in oxygen conc
if Hb was in a constant R state (high affinity)
wouldn’t work: oxygen would bind too tightly and not be given up to respiring tissue
if Hb was in a constant T state (lower affinity)
wouldn’t work: woudlnt bind oxygen well e.g. only 50% saturated- not enough oxygen in tissue
If haemoglobin showed No cooperativity
– Hb would be 60% saturated after passing the lungs and would only release 38`% to the tissues
If haemoglobin shows cooperativity (Sigmoidal)
- picks up oxygen really well, transporting twice as much oxygen than with no cooperativity and releases it really well
Gain and release of oxygen by Hb is a tightly regulated process. Which molecules affects Hb affinity for oxygen? (2)
- 2,3,- bisphosphoglycerate (BPG)
- H+ ions
the oxygen binding curve for pure haemoglobin is
different than the oxyegn bdidning cruve for hameoglobin found within RBCs
the cuvre for haemoglobin in RBC is
shifted tot he right with respect to the pure Hb curve
- implying that pure Hb has a much higher afffinity for oxygen and will release much less (only 8%) of oxygen to exercising tissue (comapred to 66% for Hb in RBC)
2,3- Bisphosphoglycerate acts as an …….. of Hb
allosteric effector
what is 2,3-BPG
is a naturally occurring molecule that is produced as an intermediate in the glycolysis process.
what does 2,3-BPG do
bidns to the centre pocket found in Hb, stabilisiing the T-state of Hb
2,3-BPG affect on Hb affinity for oxygen
stabilises the T state (low affinity)
- decreasing Hb affinity for oxygen
- shifting the entire oxygen-bdinding curve to the right side
BPG allows
Hb to act as an effective oxygen carrier in the body- unloading about 66% of oxygen to exercising tissue
what does the oxygen dissociation curve look like with and withou BPG
with BPG- sigmoidal
without BPG- hyperbolic
charge of BPG
negatively charged- can bind with positivly charged haem
BPG and altitude
At high altitudes- BPG concentration increases- promoting oxygen release in tissues
- At high altitude lower ppO2
- BPG shifts curve to the right
- Picks up less oxygen from the lungs (slighlty)
- But able to release about the same amount to the tissues due to lower affinity
why atheletes train at high altitudes
increase in BPG and RBC production
- 2,3-BPG is elevated in high altitudes, meaning Hb has a lower affinity for oxygen, releasing it more efficiently to respiring tissue.
- Haemoglobin content also increases (more RBC) so that higher amounts of oxygen can be captured.
carbon dioxide and H+ ions (acidic) affect on Hbs affinity for oxygen
- have the same affect as BPG
- lower Hbs affinity for oxygen
both CO2 and H+ bind to
Hb but not myoglobin
why do carbon dixodie and hydr0ogen ions not bind myoglobin
Myoglobin cannot exhibit the Bohr effect- only consists of a single polypeptide
Only in Hb- quaternary structure – cooperative effect
where is CO2 and H+ effect on Hb important
in active tissue
- local pH decline in metabolically acitve tissues due to the release of H+ and CO2
- decreases affinity Hb has for oxygen
- icnreases the release of oxygen from Hb
Hb has a lower affiity for oxygen at
lower pH (i.e. when tissue is metabolically active)
why is CO a poison
CO is a poison because it combines with ferromyoglobin and ferrohaemoglobin and blocks oxygen transport
CO binds to haemoglonbin …… more readily than oxygen
x250
when is CO poisoning fatal
when COHb is >50%
- binds more strongly and longer than oxygen
treatment for CO poisoning
- blood transfusion
- hyperbarix oxygen therapy
