L10- Enzyme regulation and inhibition Flashcards Preview

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Flashcards in L10- Enzyme regulation and inhibition Deck (16):
1

What are th stereoisomers of amino acids?

The NH3 is on the left- L

NH3 is on the right- D

The R and coo- group must be going away from you and the H and Nh3+ groups must be coming towards you. Like in the sugars

Nh3+ on left= L

Nh3+ on right= D

2

What kind of enzymes are jey metabolic control enzymes usually?

Allosteric

3

What atructure do most allosteric enzymes have?

Quaternary structure

With "cooperativity" between their subunits

4

Apart from the active site, what do noncovalent allosteric enzymes have?

A secondary regulatory site (allosteric site) distinct from the active site.

Allosteric inhibitors or activators bind to this site and regulate enzyme activity via conformational changes. - noncovalent allosteric regulation.

5

What is cooperativity?

Binding by a substrate to one active site affects subsequent binding to all other subunits. (to more active form usually)

6

Due to subunit cooperativity, what shape are rate versus substrate conc. plots?

Sigmoidal

7

What forms does an allosteric enzyme have?

Active form - R form

Inactive form - T form

8

What do activators and inhibitors do to enzymes?

-Binding of activators stabilizes the active form (R form)

-Binding of inhibitor stabilizes the inactive form (T form) of the enzyme.

9

What is PFK-1?

An allosteric enzyme which catalyses the early step in glycolysis. Turns fructose-6-phosphate into fructose-1,6-biphosphate.

10

What are allosteric activators and inhibitors of PFK-1?

AMP= activator

PEP= inhibitor. PEP is produced later in glycolysis so acts-- feedback inhibition

11

What do AMP and PEP affect the Km of PFK-1? 

AMP- lowers km. For a given concentration of fructose-6-phosphate, intial rate is higher. 

PEP- increases Km.

12

What does a high [pep]/[amp] ratio cause?

Higher Km

Lower PFK-1 activity

Less glycolysis

13

What are the 3 types of inhibitors?

Competitive- competes for binding site

Noncompetitive- binds to ES complex or enzyme site.

Uncompetive- binds to ES complex

14

How does each inhibitor affect vmax and Km?

Competitive- vmax unchanged, km increased

Uncompetitive- vmax decreased, km also decreased, slope the same so lines parallel

Non-competitive- vmax reduced, km unchanged

15

In the lineweaver-burk plots what will each inhibitor look like?

Competitive- will intersect on 1/Vo axis (y axis) because vmax isn't changes.

 

Uncompetitive- will have parallel lines because vmax and km are reduced.

-Non-competitive- the lines will intersect on the 1/[s] x-axis because the km does not change

16

In reality what does non competitive inhibition cause?

If it;s pure- affects only vmax. However this is very rare. It's common to have mixed inhibition which affects both vmax and km.