8.4 Transport of Oxygen & Carbon Dioxide in the Blood Flashcards
How is oxygen transported around the body?
4 O2 molecules BIND to each HAEMOGLOBIN molecule
forming OXYHAEMOGLOBIN
What type of molecule is haemoglobin?
quaternary, globular, conjugated protein
What is the formula for oxyhaemoglobin?
Hb(O2)4
Hb + 4O2 ⇌ ____
Hb(O2)4
How are erythrocytes specialised to transport oxygen?
BICONCAVE - larger surface area
NO NUCLEUS - more space for haemoglobin
HAEMOGLOBIN - high affinity for O2, can both bind REVERSIBLY to O2
What is the structure of haemoglobin?
CONJUGATED protein
2 alpha + 2 beta subunits
each subunit made from polypeptide + Fe2+ haem group
What is haemoglobin?
red oxygen-carrying pigment
with a HIGH AFFINITY for oxygen
What is a conjugated protein?
protein with PROSTHETIC GROUP
attached by COVALENT BONDS/ IONIC INTERACTIONS / HYDROGEN BONDS
What is a prosthetic group?
NON-PROTEIN component
of a CONJUGATED protein
What is partial pressure?
amount of PRESSURE exerted by a SPECIFIC TYPE of gas
in a MIXTURE of gases.
Indicates CONCENTRATION of that gas.
How is oxygen transported from the lungs to respiring cells?
- Erythrocyte enters lung capillaries.
- ppO2 in alveoli > ppO2 erythrocyte
- STEEP CONCENTRATION GRADIENT»_space; O2 diffuses
into erythrocyte
- one O2 molecule binds to haemoglobin.
- CONFORMATIONAL CHANGE»_space; ￪ affinity for O2
- O2 binds more easily - POSITIVE COOPERATIVITY.
- Erythrocyte reaches respiring tissue with high O2 saturation.
- ppO2 in erythrocyte > ppO2 in respiring cell
- STEEP CONCENTRATION GRADIENT O2
diffuses ⟶ respiring cell
- After single O2 molecule released by haemoglobin:
- CONFORMATIONAL CHANGE reversed»_space; ￬ affinity
for O2. - remaining O2 released more easily.
- CONFORMATIONAL CHANGE reversed»_space; ￬ affinity
Why does haemoglobin’s affinity for oxygen not lower after the first molecule of oxygen binds? (since there is now oxygen in the haemoglobin as well as the alveoli)
oxygen is BOUND»_space; does not change concentration of FREE OXYGEN.
binding causes conformational change»_space; increases affinity so O2 binds easier.
What is the oxygen dissociation curve?
curve showing how haemoglobin’s AFFINITY for O2 (using % saturation) changes
over different ppO2
What is the y axis on an oxygen dissociation curve and what does it indicate?
% saturation of haemoglobin
indicates affinity for oxygen
Describe haemoglobin’s affinity for O2 at low ppO2:
near RESPIRING TISSUES
few haem groups have bonded O2»_space; few undergone conformational change
LOW AFFINITY for oxygen
Describe haemoglobin’s affinity for O2 at medium ppO2:
some more haem groups have at least one bonded O2
some more have undergone CONFORMATIONAL CHANGE
EASIER for oxygen to bind to MORE haem groups
￪ AFFINITY for oxygen
Describe haemoglobin’s affinity for O2 at high ppO2:
in CAPILLARIES OF LUNGS
many haemoglobin have at least one bonded O2
many have undergone CONFORMATIONAL CHANGE
EASIER for oxygen to bind to remaining haem groups
VERY HIGH AFFINITY for oxygen`
Why does oxygen saturation never reach 100%?
Theoretically every haemoglobin can have 4 bonded O2,
but realistically very unlikely
How is the affinity for oxygen different in FETAL HAEMOGLOBIN compared to adult?
at ANY PPO2
HIGHER AFFINITY for O2
Why is it important that fetal haemoglobin has a higher affinity for oxygen than the mother’s?
O2 is taken from mothers haemoglobin + bound to fetus’ in placenta.
(same premise as displacement reaction, since more reactive metal will take non-metal from less reactive metal)
If same affinity, oxygen would not transfer
Oxygenated blood from the mother runs closely to deoxygenated blood of the fetus in what organ?
placenta
What is the bohr effect?
Effect of CO2 concentration on UPTAKE + RELEASE of O2
by haemoglobin
How does a higher ppCO2 affect haemoglobin’s affinity for oxygen?
higher ppCO2 = lower affinity for O2, due to formation of:
HAEMOGLOBINIC ACID - more CO2 = ￪ H2CO3 formed = ￪ H+ = ￪ haemoglobinic acid = ￬ Hb
CARBAMINOHAEMOGLOBIN - CO2 binds to haemoglobin»_space; cannot bind to O2
What is the importance of Bohr effect?
ACTIVELY RESPIRING TISSUES - high ppCO2 + high demand for O2.
- high ppCO2 decreases affinity of haemoglobin for oxygen»_space; O2 MORE READILY LOST in these areas.
LUNGS - low ppCO2
- low ppCO2 increases affinity of haemoglobin for oxygen»_space; O2 BINDS more EASILY
In what ways is carbon dioxide transported in the blood?
HYDROGEN CARBONATE 80%
CARBAMINOHAEMOGLOBIN 15%
PLASMA 5%
Outline the steps in which CO2 is transported via Hydrogen Carbonate.
- CO2 diffuses into cytoplasm of RBC.
- CO2 + H2O ⟶ H2CO3
- catalysed by CARBONIC ANHYDRASE
- H2CO3 dissociates ⟶ H+ + HCO3-
- pH increases
- Hb acts as BUFFER by taking H+ out of solution
- very WEAK acid so only 1% of H+ in solution
- HCO3- ions diffuse cytoplasm ⟶ plasma.
Cl- ions diffuse from plasma ⟶ cytoplasm - CHLORIDE
SHIFT.- maintains electrochemical equilibrium
- Lungs: HCO3- in plasma ⟶ H2O + CO2 by series of
reactions.- CO2 diffuses out into ALVEOLI.
What is the reaction between a proton and haemoglobin?
H+ + Hb ⟶ HHb
proton + haemoglobin ⟶ haemoglobinic acid
Why is CO2 converted into other compounds instead of being transported as CO2 molecules?
CO2 molecules in blood = less steep concentration gradient
therefore converted into other molecules to MAINTAIN STEEP CONCENTRATION GRADIENT
so that CO2 molecules can diffuse in at fast rate despite previous CO2 molecules already diffused in.
What is chloride shift?
MOVEMENT of Cl- ions INTO cytoplasm of RBC
to maintain ELECTROCHEMICAL EQUILIBRIUM
Why is Hb a good pH buffer?
reacts with H+ taking it out of solution
forming a WEAK acid. (even less H+ in solution)
In which 2 ways does a high ppCO2 lower haemoglobin’s affinity for oxygen?
- formation of carbaminohaemoglobin - reduces available Hb
2. Formation of HHb - reduces available Hb
