Hemoglobin

Question 1

What kind of oxygen saturation curve does Hb have, and what does that imply

Answer 1

Sigmoidal, implies cooperativity

Question 2

Oxygen saturation equation

Answer 2

Yo2= po2/ (p50+po2)

Question 3

Bohr effect

Answer 3

Rightward shift when co2 increases and acidity increases (ie PH decreases)

Question 4

Where does BPG bind; Effect of BPG

Answer 4

Pocket in centre of Hb tetramer in T STATE; Rightward shift

Question 5

Subunits in HbE/HbF/HbA

Answer 5

HbE: zeta2,epsilon2
           Alpha2, epsilon2
          Zeta2, gamma2
HbF: alpha2, gamma2
HbA: alpha2, beta2

Question 6

How is heme stabilised?

Answer 6

1. Hydrophobic residues on interior of protein (subunit) provide protective environment in which oxidation of Fe2+ is prevented
2. Distal histidine (E7) stabilised o2-bound form, destabilise CO

Question 7

What is one subunit made of, and how is heme group situated in it

Answer 7

8 alpha helixes connected by turns and loops,

Heme binds between helices E & F by histidine residues (proximal his at F; distal his at E)

Question 8

What happens when o2 binds to a hemoglobin subunit

Answer 8

Movement of Fe towards heme plane (0.4 Angstrom)

F Felix moves

Transition from T to R state

Question 9

What are T and R states

Answer 9

T- tense: deoxygenated

R- relaxed: oxygenated

Question 10

How much co2 and H+ does hb transport

Answer 10

Co2: 15-20%

H+: 40%

Question 11

How does Hb transport co2

Answer 11

In respiring tissues, co2 enters RBC.
CarbOnic anhydrase converts
Co2+ h20 hco3- + h+
Chloride-bicarbonate exchange protein takes in cl-, pumps hco3- out (dissolves in plasma)

In lungs,
Bicarbonate enters via chloride-bicarbonate exchange protein,
CarbOnic anhydrase converts
Hco3- + h+ h2o + co2

If Co2 isn’t converted to hco3-, it reacts with Hb n-termini to produce carb amino terminal residues

Question 12

How do carbamino residues contribute to Bohr effect

Answer 12

Presence of salt bridges stabilise T state

Question 13

Sickle cell anemia

Answer 13

Mutation that converts glu to Val in BETA chains -> hydrophobic sticky patches
Oxygenated molecules are soluble,
Deoxygenated molecules aggregate into insoluble fibres -> deform RBC into sickle shaped cells -> occlusion of blood flow

Question 14

Heme group defects put patients at risk of…

Answer 14

Porphyria diseases

Question 15

Reduced synthesis of alpha/beta chains result in….

Answer 15

Thalassemia

Question 16

Diabetic patients have increased amounts of… this can be measured by…

Answer 16

Glycosylated hemoglobin (HBA1c)

HPLC and mass spectrometry