Session 2

Question 0

Contrast the oxygen-binding properties of myoglobin and haemoglobin and explain why haemoglobin is most suited to a role as an oxygen transporter

Answer 0

Myoglobin - hyperbolic binding curve, myoglobin wouldn’t release O2 at tissues
Haemoglobin - sigmoidal binding curve, cooperative binding, O2 affinity changes - allows for efficient oxygen binding and delivery

Question 1

Explain the physiological roles of myoglobin and haemoglobin

Answer 1

Myoglobin - found in muscle tissue, provides oxygen for muscles
Haemoglobin - carries oxygen from lungs to tissues

Question 2

Describe the major structural differences between oxygenated and deoxygenated haemoglobin and the molecular basis of cooperativity

Answer 2

Oxygenated Hb - (promotes) high affinity R state
Deoxygenated Hb - low affinity T state
Cooperativity - the binding of one oxygen molecule promotes the binding of subsequent molecules

Question 3

Describe the effects of CO2, H+, 2-3-bisphosphonates and carbon monoxide on the binding of oxygen by haemoglobin and the physiological significance of these effects

Answer 3

CO2 & H+ - Bohr effect (curve shifts to right), lowers affinity for O2, ensures delivery of O2 is coupled to demand (Hb more likely to release O2)
2,3-BPG - allosteric inhibitor, lowers affinity, stabilises T state, O2 is released at tissues
CO - blocks oxygen transport, bind to Hb more readily than O2, increases affinity for O2 for unaffected subunits

Question 4

Appreciate that mutations in glob in genes can give rise to diseases such as sickle cell anaemia and thalassaemias

Answer 4

Sickle cell anaemia - mutation in gene in B-chain (glutamate –> valine), sticky HbS polymerize, crises, sickled RBCs, haemolysis
B-thalassaemia - decreased or absent B-chain production, a-chains unable to form stable tetramers, symptoms appear after birth
A-thalassaemia - decreased or absent a-chain production, B-chains can form stable tetramers with increased affinity for O2, onset before birth

Question 5

Explain the effects of enzymes on chemical reactions

Answer 5

Enzymes increase the rate of reaction by lowering the activation energy by facilitating the formation of the transition state

Question 6

Describe how reaction rates vary as a function of enzyme and substrate concentration

Answer 6

The rate of an enzyme catalysed reaction is related to the concentration of substrate

Question 7

Define the terms: activity, international unit of enzyme activity, Km and Vmax

Answer 7

Activity - the measure of the ability of an enzyme to catalyse a specific reaction
International unit of enzyme activity - one U is the amount of enzyme that catalyses the conversion of 1 micro mole of substrate per minute
Km - substrate concentration that gives half Vmax
Vmax - maximum velocity when all enzyme active sites are saturated with substrate

Question 8

Describe the effects of enzyme inhibitors on enzyme kinetics and be able to distinguish between the two from simple graphs

Answer 8

Inhibitor - molecules that slow down or prevent an enzyme reaction
Competitive inhibitor - affects Km not Vmax
Non-competitive inhibitor - affects Vmax not Km