7: Enzyme kinetics and Creatine Kinase

Question 1

Vmax

Answer 1

maximum speed the reaction can go

-levels out when saturated

Question 2

Kmax

Answer 2

Point of half of Vmax

How much substrate will make an enzyme work half as fast

Question 3

Low Kmax

Answer 3

strong binding of enzyme to substrate

Question 4

High Kmax

Answer 4

weak binding of enzyme to substrate

Question 5

Competitive inhibitors

Answer 5

structurally similar to substrate
competes with substrate to bind at active site
increasing substrate can overcome inhibition
Kmax increases, Vmax doesn’t

Question 6

non-competitive inhibitors

Answer 6

structurally different from substrate
bind to enzymes on allosteric site
Increasing substrate does not overcome inhibition
Vmax decreases, Km remains the same

Question 7

Creatine Kinase is

Answer 7

an enzyme present in most tissues at relatively low levels

present at higher levels in the brain, heart, skeletal muscle as they have higher metabolic activity

Question 8

Creatine kinase catalyses

Answer 8

ATP <—> creatine phosphate + ADP

Question 9

Creatine kinase is used by cells as

Answer 9

an energy buffer

Question 10

Creatine kinase structure

Answer 10

dimeric protein
2 genes code for 2 different monomers
M and B

Question 11

What creatine kinase monomers do skeletal muscles produce

Answer 11

MM only

Question 12

What creatine kinase monomers does the brain produce

Answer 12

BB only

Question 13

What creatine kinase monomer does the heart muscle produce

Answer 13

only cell transcribing both genes, mainly produces MB but also some MM and BB

Question 14

What happens when cells are damaged to creatine kinase levels

Answer 14

CK is release into the bloodstream, its activity can be measured using a coupled assay

Question 15

Cardiac Troponin I is a

Answer 15

Highly specific and sensitive marker For myocardial injury
Commonly used to diagnose myocardial infarction

Question 16

Aspartate transaminase (AST)

Answer 16

Can be elevated in setting of myocardial infarction
Not specific and used less frequently

Question 17

Alkaline Phosphate (ALP)

Answer 17

Not typically used as a bio marker for myocardial infarction
More commonly used with liver and bone disease diagnosis

Question 18

Lactate dehydrogenase (LDH)

Answer 18

Can be elevated following myocardial damage
Less specific and less commonly used

Question 19

Creatine kinase - MB
(CK-MB)

Answer 19

Used to assess cardiac damage
Especially useful for diagnosing myocardial infarction
Although cardiac troponins more specific

Question 20

How long after a myocardial infarction, do cardiac Troponin I and T levels remain elevated in serum?

Answer 20

5 days

The exact duration of elevation may vary depending on factors such as the extent of myocardial damage and individual patient characteristics.

Question 21

In a Lineweaver-Burk plot the slope, Y intercept and X intercept can be calculated different equations. What are the characteristics of this graph

Answer 21

Slope=Km/Vmax, Y intercept = 1/Vmax, X intercept = -1/Km

Question 22

Michaelins constant

Answer 22

conc. of substrate at which enzyme works at half its max velocity
KM = -1/intercept

Question 23

Which type of peptide bond does chymotrypsin specifically cleave?

Answer 23

Bonds between bulky hydrophobic side chains

• due to presence of hydrophobic pocket in chymotrypsin active site which accommodates bulky hydrophobic amino acid residues such as phenylalanine, tryptophan and tyrosine

Question 24

Following a severe Myocardial infarction, a patients blood test shows significantly elevated levels of a certain creatine kinase isoenzyme.

Answer 24

MB
- cardiac-specific isoenzyme
- typically rise within hours of MI, peak at 24-48h
return to normal within 48-72h