Willmott 8 Myoglobin and Haemoglobin

Question 1

Haemoglobin
function:
size:
form:

Answer 1

• Oxygen-carrying protein in red blood cells (easily acessable)
• Tetramer with polypeptide chains in α2β2 complex:
• α type = 141 amino acids 
β type = 146 amino acids (all helixes)
• Contains essential prosthetic group 
(haem - with Fe atom)

Question 2

Haemoglobin

saturation curve

Answer 2

• SigmoidalO2-bindingcurve (cooperativity)

Question 3

Hb – pathway of communication

Answer 3

• O2 binds to Fe2+
• Fe2+ moves 0.7 Angstrom into plane of ring
• Pulls Histidine side chain towards ring
• Histidine residue is in F-helix which moves by several
• Breaks interactions (electrostatic) at subunit interface allowing relative rotation of subunits

Question 4

O2 binding to Hb affected by…

Answer 4

• H+ favours deoxy form (acidic conditions)

• CO2 favours deoxy form
• BPGbinds1pertetramer (biphosphoglycerate)
• stabilises deoxy form

• All these effectors promote O2 release in tissues

Question 5

Lactate acid effect

Answer 5

= acidic => favour O2 release

Question 6

Oxygenation of Hb

Answer 6

Moves Fe 2+ into centre of porphyrin ring

Question 7

BOHR EFFECT

Answer 7

25% drop max binding by pH

Question 8

Two effects of CO2 on Hb

Answer 8

• Generates H+ (acid)

• binds directly to Hb amine groups
CO2 + H2O   H2CO3    H+ + HCO3- Carbonate ion
-NH2 + CO2 -> N COO-
H
Carbamate ion

Question 9

bis =

Answer 9

2P bonded separatley to C backbone

Question 10

BPG effect on Hb

Answer 10

Reduces affinity of Hb for O2

Question 11

Foetal haemoglobin
subunit strucutre:
function:
amino a difference:

Answer 11

• α2γ2 subunit structure

• Binds BPG less tightly than adult Hb (α2β2 )

• Therefore binds O2 more tightly than adult Hb
• Oxygen can pass from mother’s blood to foetus
gamma chains
Ser 143 NOT His 143 -> not same +/ve charge => favour oxygenated state

Question 12

Sickle cell anaemia

Answer 12

• Disease caused by defective Hb
• point mutation in β chain (Glu6 to Val) A-> T -/ve -> non-polar => hydrophobic -> hydrophobic

• Leads to loss of solubility and precipitation in red blood cells

Question 13

Heterozygous individuals have

Answer 13

increased resistance to Malaria

Question 14

Tripsin =

Answer 14

protease in sequence preference to cut 2D chromatography