enzyme II: enzyme kinetics

Question 1

what is enzyme kinetics?

Answer 1

The study of the rate of an enzyme controlled reaction (to see the effect of substrate concentration, of different inhibitors/drugs or different isozymes/mutations)

Question 2

what is The Michaelis-Menten equation?

Answer 2

Vo= Vmax [S] /Km+ [s]

Question 3

what does Vmax represent ?

Answer 3

Here, Vmax represents the maximum velocity achieved by the system at saturating substrate concentrations.

Question 4

what does the Km represent ?

Answer 4

Km (the Michaelis constant) is the substrate concentration at which the reaction velocity is 50% of the Vmax.
[S] is the concentration of the substrate S.

Question 5

what does a high

Vmax and a low Km say about an enzyme ?

Answer 5

A fast, efficient, specific enzyme has a high
Vmax and a low Km
high Vmax allows fastest rate of reaction.
Low Km means fast reaction rate at low concentrationof substrate.

Question 6

which type Km and Vmax is more responsive to substrate concentration near saturation ?

Answer 6

high Vmax but low Km .

Question 7

how can you tell the difference between isozymes?

Answer 7

Km often used to distinguish between different forms of the same enzyme (isoenzymes).

Question 8

how is the Km related to substrate concentration in cells?

Answer 8

Km of an enzyme for a substrate is often near the concentration of that substrate in a cell, allowing enzymes to be more responsive to substrate concentrations

Question 9

what reaction does hexokinase catylyse

Answer 9

Hexokinase catalyses phosphorylation of glucose to Glucose-6-Phosphate

Question 10

what inhibits hexokinase?

Answer 10

inhibited allosterically by Glc-6-P

Question 11

what is the normal glucose conc in the blood stream and in the cell?

Answer 11

Norm blood conc=5mmol/L so in intracellular levels are 0.2-2mmol/L

Question 12

what is the Vmax and Km of hexokinase?

Answer 12

Heokinase is efficient (50-90% Vmax) under normal conditions

Has a low Km (0.2mmol/L)

Question 13

where is glucokinase found?

Answer 13

Hepatocytes (store glucose as glycogen) and pancreatic β cells contain glucokinase

Question 14

whats is the km value of glucokinase ? i it inhibited by anything?

Answer 14

Glucokinase has a Km of 10mmol/L & is not inhibited by Glc-6-P

Question 15

what is the function of Glucokinase and how is it importent?

Answer 15

Its activity increases after a meal
Results in storage of glucose & release of insulin
Mice lacking the enzyme die within 3days due to sever hyperglycaemia

Question 16

what occurs to alcohol when consumed

Answer 16

Sensitivity of some people to alcohol
Exhibit facial flushing and tachycardia after small amounts of alcohol

alcohol converts into acetaldehyde by enzyme called Alcohol dehydrogenase.

Question 17

what enzyme processes acetaldehyde.

Answer 17

The acetaldehyde is processed by aldehyde dehydrogenase

Question 18

There is two forms of aldehyde dehydrogenase , where are they found

Answer 18

aldehyde dehydrogenase:
a low Km mitochondrial and
a high Km cytoplasmic form

Question 19

Sensitivity of some people to alcohol is due to a mutation that occurs. what is this mutation and why do they show this symptom.

Answer 19

Due to a mutation some people lack the mitochondrial form od aldehyde dehydrogenase .

High concentrations of acetaldehyde need to build before a high rate of catalysis can occur due to lack of low Km enzyme.

Question 20

how is Vo measured?

Answer 20

Lineweaver-Burk plot

Vmax is achieved at infinite substrate concentration, so it is impossible to estimate Vmax and Km from a hyperbolic plot
Vo is measured at different [S] then a plot of 1/Vo against 1/[S] is made