Haemoglobin Structure And Function Flashcards
What is haemoglobin made up of?
2 alpha and two beta chains
How much of RBCs is comprised of a globular haemoprotein
1/3
What is a haemoprotein?
A group of specialised proteins that contain haem as a tightly bound prosthetic group
What is haem a complex of?
Protoporphyrin IX and ferrous iron Fe2+
How is the iron held in the centre of the haem molecule?
Bonds to the 4 nitrogens of a porphyrin ring
How much Hb is synthesised in the erythroblasts?
65%
How much Hb is synthesised at the reticulocyte stage?
35%
What is haemoglobin synthesis stimulated by?
Tissue hypoxia (lack of oxygen)
How is Hb synthesis stimulated by tissue hypoxia?
Hypoxia causes the kidneys to increase EPO production which increases RBC and Hb production
What does EPO Stand for?
Erythropoietin
What molecule delivers iron to the reticulocyte?
Transferrin
Where does synthesis of protoporphyrins take place?
In the mitochondria of RBC precursors
What is synthesis of protoporphyrins mediated by?
EPO and vitamin B6
Protoporphyrin + iron->
Haem
What are the starting reactants in the synthesis of protoporphyrin?
Glycine + succinyl CoA
What is the iron stored as if you don’t need it?
Ferritin
Where does synthesis of globin happen?
In the ribosome and RER
What does proper globin synthesis depend on?
Genes
How many functional globin chains are there?
8
What are the two clusters of globin called?
A and B
What genes are in the B-cluster?
Beta, gamma, epsilon and delta
Where are the B-cluster genes found?
On the short arm of chromosome 11
What genes are in the A-cluster?
Alpha and zeta
Where are the A-cluster genes found?
Short arm of chromosome 16
What types of globulin are found in foetal Hb?
Alpha and gamma
What types of globulin are found in adult Hb?
Alpha and beta
What are the functions of haemoglobin?
- carry oxygen from the lungs to the tissues
- remove CO2
- buffering action- maintains blood pH as it changes from oxyhaemoglobin to deoxyhaemoglobin
How many oxygens can one Hb bind to?
Four
How long does it take for Hb oxygenation?
Less than 0.1 seconds
What happens (physically) to the Hb when it’s oxygenated?
2,3-DPG is pushed out and the beta chains move closer
What does DPG stand for?
Disphosphateglycerate
What does the amount of o2 bound to hb and released to tissues depend on?
pO2
pCO2
Affinity of hb for O2
What does oxygen affinity determine?
The proportion of o2 released to the tissues or loaded onto the cells at a given pressure
What is the Bohr effect?
Alterations in the blood pH shifted the oxygen dissociation curve
What happens to the oxygen dissociation curve in acidic pHs?
The curve shifts to the right
What happens when the oxygen dissociation curve shifts to the right?
Results in an enhanced capacity to release o2 where it is needed
What does the normal position of the haemoglobin oxygen dissociation curve depend on?
2,3 DPG concentration
Hydrogen ion conc (pH)
CO2 in RBC
Structure of Hb
What are standard conditions for the Hb- O2 dissociation curve?
37 Celsius
pH 7.4
BE =0
What are the three mechanisms for CO2 transport?
Dissolution in the plasma
Formation of carbonic acid
Binding to form carbaminohaemoglobin
What is oxyhaemoglobin made up of?
Hb and 02
What is deoxyhaemoglobin made up of?
Hb - o2
What is methemoglobin made up of?
Hb with Fe3+
What is carbaminohaemoglobin made up of?
CO2 binds non-covalently to globin chain of Hb
