Chapter 2.5

Question 1

What are the four types of reversible inhibition

Answer 1

1) Competitive inhibition
2) Noncompetitive inhibition
3) Mixed inhibition
4) Uncompetitive inhibition

Question 2

Describe the characteristics of competitive inhibition? Can it be overcome? Also answer whether vmax can be changed and if the value of Km changes as well.

Answer 2

• simply involves the occupancy of an active site by an inhibitor
• yes it can be overcome
• > by simply adding more substrate
• > so that substrate to inhibitor ratio is higher
• vmax does not change
• > because if enough substrate is added, the inhibitors will be out competed
• Km does increase
• > substrate concentration does have to be higher to reach 50% activity of the vmax value

Question 3

Describe the characteristics of non-competitive inhibitor. Describe its binding to enzyme/ enzyme-substrate complexes. Also talk about how the values of vmax and Km are affected

Answer 3

• it binds to the ALLOSTERIC site instead of the active site
• > this induces an enzyme conformation change

-they bind equally well to enzyme/enzyme-substrate complexes

• vmax would decrease
• > because less of the enzyme is available
• Km wouldn’t change
• > because adding more substrate wouldn’t really change the number of enzyme-substrate complexes that form

Question 4

Describe the characteristics of a mixed inhibitor. Its ability to bind to either the enzyme or the enzyme-substrate complex. Describe how Km and vmax are affected

Answer 4

• they can bind to either the enzyme or the enzyme-substrate complex
• > has different affinity for each

-they bind to the allosteric sites, not the active sites

For enzyme binding
->it increases the Km

For enzyme-substrate complex binding
->it decreases the Km

• in either cases listed above
• > vmax decreases

Question 5

Describe the characteristics of the uncompetitive inhibitor. Do they bind to substrate or substrate-enzyme complex. What happens to Km and Vmax?

Answer 5

• they only bind to the enzyme-substrate complex
• > enzyme locks substrate in place
• > preventing its release
• > this can increase the affinity for the enzyme
• note uncompetitive inhibitors bind to allosteric sites
• > Km is lowered and vmax decreases as well

Question 6

What is meant by irreversible inhibition

Answer 6

• the active site is made unable for a prolonged period of time
• > or the enzyme is permanently altered
• > this type of inhibition is not easily overcome or reversed

-eg; aspirin

Question 7

What is glycosylation used for?

Answer 7

• it is the covalent attachment of sugar compounds
• > a covalent enzyme modification
• > it can be used for transport within the cell or can modify protein activity/selectivity