Lecture 10 - Enzyme inhibition and control

Question 1

Allosteric enzyme

Answer 1

Activity controlled through a 3D structure brought about by small molecules exhibiting cooperativity

Question 2

Allosteric regulatory site

Answer 2

Distinct from the active site and is used to regulate enzymatic activity through conformational changes

Activator - stabilises the active (R) form
Inhibitor - stabilises the inactive (T) form

Question 3

Cooperativity

Answer 3

Binding by a substrate to one active site affects all other binding sites

Question 4

Inactive form

Answer 4

No substrate bound - inactive form present

Question 5

Stabilised active form

Answer 5

Substrate bound - all subunits locked into the active conformation

Question 6

PFK-1: what do ADP and PEP do?

Answer 6

Adenosine diphosphate signals to the cell that glycolysis is needed so PFK-1 is activated and fructose-6-phosphate is glycolysed into fructose-1,6-bisphosphate

Phosphoenolpyruvate signals to the cell that sufficient glycolysis has occurred so PFK-1 is inhibited and stabilised in the inactive form and the glycolysis of fructose-6-phosphate occurs at a lower rate

Question 7

Allosteric regulators: how do they affect the velocity over time?

Answer 7

Affect Kₘ (not Vₘₐₓ)

Activator - Lower apparent kₘ value -> velocity incr
Inhibitor - Higher apparent kₘ value -> velocity decr

Question 8

Enzyme inhibition: what are the three types and what do they do?

Answer 8

Competitive - Bind to the active site, preventing substrate binding (increasing kₘ)
Uncompetitive - Bind to the enzyme-substrate complex, causing conformational changes and preventing degradation (decreasing kₘ and Vₘₐₓ)
Noncompetitive - Binds to another allosteric site, preventing substrate breakdown (decreasing Vₘₐₓ)

Question 9

Competitive, noncompetitive, and uncompetitive inhibition graphs:

Answer 9

google?

https://www.ncbi.nlm.nih.gov/books/NBK545242/figure/article-25953.image.f1/

com - x, km inc, vmax dec
noncom - l/, km unaff, vmax dec
uncom - //, km dec, vmax dec