Transport in Animals - Erythrocytes and Haemoglobin Flashcards
what are the adaptations of erythrocytes
- very small
- biconcave disc
- no nucleus, mitochondria or ER
how does being very small help erythrocytes
- short diffusion distance
- squeeze through capillaries so in close contact with tissues
how does a biconcave disc help erythrocytes
larger surface area to volume ratio
how does no nucleus, mitochondria or ER help erythrocytes
leaves more space for haemoglobin - combines reversibly with oxygen to form oxyhaemoglobin
which of the following functions can be carried out in a mature red blood cell:
- protein synthesis
- cell division
- lipid synthesis
- respiration
respiration - anaerobic respiration can occur in the cytoplasm
what is haemoglobin
- a globular protein molecule made of four polypeptide chains
- each polypeptide has a haem prosthetic group containing a single iron ion (Fe2+)
describe the haem group
has an affinity for oxygen - the iron ion can attract and hold one oxygen molecule
describe the formation of oxyhaemoglobin
- formed in the lungs
- reversible reaction
where is the oxygen released
in body tissues, this is called dissociation or unloading
Describe the process of taking up oxygen
- in the alveoli of the lungs oxygen molecules diffuse into the blood plasma
- oxygen molecules bind to the haemoglobin forming oxyhaemoglobin
What maintains a steep concentration gradient in the process of taking up oxygen
- Taking oxygen out of solution maintains a steep concentration gradient
- Therefore more oxygen enters the blood and diffuses into the red blood cells
Describe the process of releasing oxygen
- Oxygen molecules are needed in the tissues for aerobic respiration
- Oxyhaemoglobin dissociates releasing the oxygen
What does haemoglobins affinity for oxygen depend on
The partial pressure of oxygen (pO2)
What is partial pressure of oxygen
A measure of oxygen concentration
What is the relationship between haemoglobins affinity for oxygen and pO2
As pO2 increases, so does Hb’s affinity for oxygen
What happens when there’s a high pO2
Oxygen loads onto Hb to form oxyhaemoglobin
What happens when there’s a lower pO2
Oxyhaemoglobin unloads its oxygen
describe loading at alveoli in the lungs
- high pO2 (12-14kPa)
- Hb has a high affinity for O2
- oxygen loads
- Hb 96-97% saturated
describe unloading at respiring tissue
- low pO2 (2-5kPa)
- Hb has a low affinity for O2
- oxygen unloads/dissociates
- Hb 20-70% saturated
what does a haemoglobin dissociation curve show
the affinity of haemoglobin for oxygen at different partial pressures of oxygen
what is the shape of a haemoglobin dissociation curve
s-shaped (sigmoid)
why is the first part of the curve not very steep
the first O2 molecule combines relatively slowly with the first haem group.
what happens after the first binding
the binding of oxygen with the first haem group causes the shape of the whole haemoglobin molecule to change
why does the curve become steeper
as a result of its altered shape, it is much easier for the second and third O2 molecules to bind to their haem groups
why does the curve flatten off
it then becomes much harder for the fourth (ie last) oxygen molecule to combine with the fourth haem group
do the same shape changes occur during dissociation
yes
