Regulatory Enzymes

Question 1

How do enzymes work?

Answer 1

reactions take place in the active site which has high affinity for substates. active site provides an environment conducive to the reaction, bind to substates transition state

Question 2

What curve is Michaelis Menten?

Answer 2

hyperbolic

Question 3

What is a regulatory enzyme?

Answer 3

most enzymes are not regulatory. usually catalyze reactions that are:
-early in the pathway
-immediately after branch points
-far from equilibrium

Question 4

What are the mechanisms of enzymes?

Answer 4

Rapid regulation:
-allosteric enzymes
-covalent modification
Slower:
-altered enzyme concentrations (changes in gene expresion, degradation)

Question 5

What is an allosteric enzyme?

Answer 5

a change in the shape and activity of an enzyme that results from molecular binding with a regulatory substance at a site other than the active site

Question 6

What is an example of an allosteric enzyme?

Answer 6

feedback inhibition- most studied
ATCase inhibition

Question 7

What kind of kinetics does an allosteric enzyme show?

Answer 7

sigmoid kinetics, no Km (K0.5)

Question 8

What are the 2 classes of allosteric regulation?

Answer 8

Homotropic: regulator is usually the substrate, binding to the active site increases the activity of the other active sites
Heterotrophic: modulators are generally metabolites or other small molecules, bind somewhere distinct to the active site

Question 9

What are the two conformations of cooperativty?

Answer 9

T-state: low activity, stabilized by inhibtors
R-state: high activity. stabilized by activators

Question 10

What are the 2 models of cooperativity?

Answer 10

-concerted: all subunits either in T or R state, oxygen shifts equillirium
-sequential: binding of oxygen causes a conformational change shifting T to R-state

Question 11

What is regulation by covalent modification?

Answer 11

Phosphorylation! FAST!
Kinases- add phosphate
Phosphatase: remove phosphate

Question 12

Explain phosphorylation.

Answer 12

Usually on a serine, threonine, sometimes tyrosine
hydroxyl is the phosphorylation site
can be complex

Question 13

What is altered gene expression?

Answer 13

-transcription of specific genes regulated by numerous transcription factors
-can alter concentration of enzymes and other proteins
-transcription factors bind to promoters to regulate transcription
-complex and SLOW
ex: PEP carboxykinase