Blood Biochemistry 3
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Why does oxygen have to be bound to Hb to be transported to tissues?
As it has a low solubility and cannot move freely through the plasma
What is the haem part of Hb composed of?
An organic part (C,H,O,N) and a central iron atom
Is the haem group hydrophilic or hydrophobic?
Why is the protein part of a haem group needed?
- It makes the protein soluble
- Isolated haem (without the protein) undergoes a process of oxidation where the Fe2+ ion changes to a Fe3+ ion when oxygen binds. Globin molecules in this form can no longer carry O2. This can only happen when haem groups are allowed to come together to form an intermediate step. The distal histidines in haemoglobin prevent oxidation of the Fe2+ ion (as they prevent the formation of the intermediate compound). This keeps the iron in the oxygenated form.
Dital histidines significantly decrease the affinity for what compound in haemoglobin and myoglobin?
What are the differences between myoglobin and haemoglobin?
- Myoglobin - O2 storage in muscles, 1 polypeptide chain/1 haem group, 1 O2 binding site per molecule, not an allosteric protein
- Haemoglobin - transports O2 to tissues using RBCs, 4 polypeptides chains/4 haem groups, 4 O2 binding sites per molecule, Allosteric protein
Why is haemoglobin an allosteric protein?
As it has 4 subunits which interact - the binding at 1 site affects the shape / affinity of other sites
What are the differences between deoxy Hb and oxy Hb?
- Deoxy Hb - lower O2 affinity, tense form, extra ionic bonds, also ionic bonds with 2,3, BPG (which stabilises T form)
- Oxy Hb - Higher O2 affinity, relaxed form, rotation at contact points
What has a higher affinity for O2, myoglobin or haemoglobin?
Give some examples of allosteric effectors of Hb
What do allosteric effectors do?
- They decrease the Hb affinity for O2
- Stabilise the deoxy Hb (T form)
- Promote release of O2
- Move the sigmoid curve to the right
Cattle, sheep and goat Hb is not responsive to 2,3 BPG. How do they react to situations of oxygen depletion?
- They produce more EPO to increase RBC production.
- Bovine oxyglobin is fully saturated with O2 and releases it easily. It can therefore be used to treat anaemia or hypoxia (as it is not a part of the RBC so you don't have to match blood types and it can be given to other species without causing a reaction).
Where is haem mainly synthesised?
In the liver and early RBCs (erythroblasts and reticulocytes)
What are some of the clinical signs of defects in haem synthesis?
- Red/brown discolouration of teeth and bones
- Photodermatitis (UV damage to lipids and proteins)
- Anaemia (RBC damage)
What happens to the components of haem when RBCs are broken down?
- Globin part - hydrolysed to constituent AAs
- Haem - recycled
When RBCs prematurely lyse in the plasma what protein binds the Hb?
What is a potentially toxic product of the breakdown of haem?
How is bilirubin removed from the body?
It is bound to albumin which transports it to the liver to be processed in bile and excreted from the body
What disease is caused by elevated bilirubin levels in the plasma? What clinical signs does it cause?
- Yellow colour to skin and mucus membranes
What does jaundice indicate?
- Excessive breakdown of RBCs
- Decrease in albumin level/binding
- Impaired liver function
- Obstruction of bile duct
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