Enzyme Kinetics

Question 1

list 3 characteristics of enzymes

Answer 1

act as catalysts - disease implications if altered
specific - can diagnose
control well defined chemical reactions - can be used to investigate diagnostic tools and therapies

Question 2

describe the micheais menten model

Answer 2

Km explains relationship between Vmax and Km
Substrate > (+enzyme) > product
Substrate + enzyme (ES) = very unstable so can go back the way and not progress to product

Question 3

how is michealis menten constant (Km) derived?

Answer 3

Km = K-1 + K2/K1
K-1 = backwards reaction for enzyme dissociation from substrate
K1 = forward reaction for enzyme association with substrate
K2 = forward reaction of enzyme conversion of substrate to product

Question 4

what is Vo and how is it derived from a graph?

Answer 4

initial reaction velocity at known substrate conc

Found by taking initial slope of curve

Question 5

what is the michealis menten equation?

Answer 5

describes rate of catalysis as a function of substrate concentration
V = (Vmax X [S]) / (Km + [S])
- for a hyperbola
1/V = (Km/Vmax) X (1/[S]) + (1/Vmax)
- for a straight line

Question 6

what are the axes on a lineweaver Burke plot graph?

Answer 6

1/V against 1/[S]

Question 7

when does Km = [S]?

Answer 7

at 0.5 Vmax

Question 8

why is low Km of hexokinase useful in red blood cells?

Answer 8

maintains energy production via glycolysis even if glucose levels fall

Question 9

why is high Km of glucokinase useful in liver and pancreas?

Answer 9

enables glucose sensing and homeostasis
its abundance in liver regulated by insulin
excess blood glucose is metabolised

Question 10

what is MODY and what causes it?

Answer 10

maturity onset diabetes of the young
caused by lack of glucokinase activity
causes loss of insulin-mediated glucose homeostasis

Question 11

what are proline hydroxylases?

Answer 11

regulate HIF transcription factors
enables oxygen sensitive oxygen sensing over physiological ranges of PO2
High Km for O2

Question 12

what is Von Hippel Lindau Syndrome?

Answer 12

loss of prolyl hydroxylase > excessive blood vessel growth > haemangiomas in brain > subcutaneous heamangiomas track down spinal cord

Question 13

give a clinical example of competitive inhibition

Answer 13

methanol poisoning
methanol acts as substrate for ADH > causes severe tissue damage and blindness due to conversion to formaldehyde, also drives metabolic acidosis > ADH Km for ethanol 20X larger than methanol

Question 14

how is methanol poisoning treated?

Answer 14

40% ethanol in combination with dialysis and ventilation

Question 15

do allosteric enzymes follow michaelis menten kinetics?

Answer 15

no
increasing substrate conc results in sigmoidal curve instead of hyperbola
shows co-operative behaviour

Question 16

give an example of allosteric regulation

Answer 16

binding of oxygen to haemoglobin

positive co-operativity, controlled by H+, CO2, 2,3 bisphosphoglycerate

Question 17

is inhibition of rate limiting enzymes by end product a common mechanism of allosteric or active site control?

Answer 17

allosteric

Question 18

how can end products inhibit rate limiting enzymes?

Answer 18

produced at end of biochemical pathway and inhibit the slowest enzyme. This effectively shuts down further enzymes by limiting their substrate availability.