Hemoglobin

Question 1

6 types of chains (sub-types) of globin

Answer 1

a-like chains : zeta and alpha

B-like chains: epsilon, gamma, delta, beta

Question 2

Different types of hemoglobin (embryonic, fetal, and adult)

Answer 2

Embryo: Hb Gower 1 (zeta2-epsilon2) etc…
Fetal: Hb F (alpha 2-gamma2) (Gamma cannot bind 2,3 BPG)
Adult: Hb A (alpha2-beta2), Hb A2 (alpha2-delta2)

Question 3

Structure of hemoglobin

Answer 3

Porphyrin ring and Fe2+
Porphyrin ring: heterocyclic tetrapyrrole (very stable)
Planar and hydrophobic
Bound to globin chain
One Fe2+ per chain (four per tetrameric molecule) O2 binding

Question 4

F8 and E7

Answer 4

F8 : where the iron binds (histidine group is proximal to iron)
E7 : Distal histidine, close to the heme but not attached to the iron

Question 5

Function of Hb

Answer 5

Transport O2

Question 6

Mechanism for O2 binding

Answer 6

Fe2+ : O2 binding site
Cooperativity
Reversibly Binding
Allosteric Control

Question 7

Structure of myoglobin

Answer 7

Is a monomer
One globin chain (different gene)
One Heme-Fe2+
(No allosteric control, no cooperativity)

Question 8

Cooperativity

Answer 8

The binding of O2 to one site increases the affinity at other sides
Either in the T state or R state… T state has much less affinity for O2
(a Hb with 3 occupied sites is 20x more likely to bind the last O2 than for a new Hb to bind its first)

Question 9

2,3- BPG

Answer 9

Lowers the oxygen affinity of hemoglobin dramatically
Sits in the middle of the Hb tetramer. This holds the tetramer back from switching to the R state, so more binding sites must pick up O2 before the switch is made.
Allosteric effector
In fetal blood the affinity for 2,3-BPG is reduced thus increasing the affinity for oxygen allowing for more O2 exchange between mother and child.

Question 10

Carbon Monoxide

Answer 10

Binds at the same place as O2 in Hb. Only binds 200x more tightly than does O2.

Question 11

Negative Allosteric Factors

Answer 11

Protons (low pH), CO2, and 2-3 BPG

Question 12

Structure of hemoglobin

Answer 12

Globin Chains : Hemoglobin is a tetramer (four sections)… best described as a pair of identical aB dimers that associate to form the tetramer.
Each Globin chain is made of 8 a-helicies (6 different types but mostly alpha and beta chains are present)
Porphyrin ring and Fe 2+