Allostery and Regulation I

Question 1

What is allosterism?

Answer 1

Controlling when binding of small molecules helps to control the activity of enzyme.
The substrate is affecting the enzyme by its binding.

Question 2

What are allosteric switches related to? ON or OFF OR volume switches?

Answer 2

volume switches

Question 3

What is covalent modification

Answer 3

When you make or break covalent bonds. When you break a peptide bond you usually activate something

Question 4

What happens if there isn’t a substrate available for the enzyme?

Answer 4

If the substrate is not available then there is no way the enzyme can be active.

Question 5

If the km is high the you will need ___ of substrate to activate the enzyme.

Answer 5

a lot

Question 6

What types of plots do allosteric enzymes give?

Answer 6

Give sigmoidal plots

Question 7

What types of plots do Homotropic Effectors give?

Answer 7

These give sigmodial curves, so the substrate affects the enzyme.

Question 8

What types of plots do Heterotropic Effectors give?

Answer 8

Models noncompetitive plots.

Question 9

What are homotrophic effectors?

Answer 9

They are substrates and effectors that affect an enzyme.

Question 10

What is an example of a homotrophic effector of ATCase? and what does it favor?

Answer 10

Aspartate

Binding of Aspartate by ATCase Favors the R-state so additional Substrate Binding is Favored.

Question 11

What are heterotrophic effectors?

Answer 11

Heterotrophic effectors are not the substrate of an enzyme, but do affect the enzyme.

Question 12

What is an example of a heterotrophic effector?

Answer 12

Activator (ATP)

Inhibitor (CTP)

Question 13

What type of subunits do ATCase contain? and what do they bind to?

Answer 13

Contains 6 regulatory subunits
ATP and CTP bind to regulatory sites

Contains 6 catalytic subunits
Aspartate bind to catalytic subunits and favors R state

Question 14

What does ATCase catalyze?
and what step does play in synthesizing pyrimidine nucleotides
CTP, UTP, DDTP

Answer 14

It starts with Carbomoyl Phoshate and its end product is an intermediate (Carbamoyl Aspartate ) that is necessary to synthesize pyrimidine nucleotides. IT’S THE FIRST STEP IN MAKING PYRIMIDINE NUCLEOTIDES.

Question 15

How does ATP affect ATCase?

Answer 15

In the Presence of ATP, the V0 is increased compared to No ATP

ATP activates ATCase (converts to R State)

Question 16

How does CTP affect ATCase?

Answer 16

This indicates that you have plenty pyrimidines and that you need to start making purines.

CTP Reduces the activity of ATCase- Converts to T State

V0 decreases as [CTP] increases

Question 17

Aspartate is a Substrate of ATCase. So how does the concentration of aspartate affect the activity of ATCase.

Answer 17

At Low [S], ATCase in T State

At High [S], ATCase mostly in R State

As [S] increases, ATCase increasingly in R State

Question 18

When is ATCase most active?

Answer 18

ATCase is most active when energy (ATP) is high, When Pyrimidines (make CTP) are Low in concentration relative to purines (make ATP)

Question 19

What determines if CTP inhibits ATCase or ATP activating it? Who wins the race?

Answer 19

Km and Concentration

This is evidence of complementary

Question 20

What are zymogens?

Answer 20

Inactive forms of enzymes

Question 21

How are zymogens activated?

Answer 21

They are activated by cutting specific peptide bonds that allow for access of the substrate to the active site. Its an ON/OFF switch. There is a cascade system where at each level you have a chain of enzymes that get activated.

Question 22

What is an example of zymogen being activated?

Answer 22

o	Chymotrypsinogen (inactive)
♣	Trypsin- Peptide bond Broken at 15-16

o Pie-Chymotrypsin (Partly Active)
♣ Acts on Pie-Chymotrypsin and cuts at 146-149

o Alpha-Chymotrypsin (Fully Active)
♣ We lose 147-148
♣ The active site is becoming fully exposed.