Term 1- Lec 12- Enzyme Regulation

Question 1

The rate limiting step of glycolysis is

Answer 1

Glucose to Glucose-6-P—this is an irreversible step

Question 2

Product Inhibition at low [S]

Answer 2

Resembles comopetitive inhibition

Question 3

Protuct Inhibition at high [S]

Answer 3

Competitive inhibition because the P far out number the S, thus inhibiting the enzyme.

Question 4

T/F: Product Inhibition is a form of feedback inhibition?

Answer 4

It is not the same as feedback inhibition

Question 5

The rate limiting step of gluconeogenesis is

Answer 5

Pyruvate to Phosphoenolpyruvate

Question 6

How do allosteric and non-competitive inhibition differ?

Answer 6

NC Inhibition binds directly onto the enzyme. Allosteric inhibition binds a regulatory subunit connected to the enzyme or catalytic subunit

Question 7

Km for allosteric enzymes is called

Answer 7

K0.5

Question 8

What type of curves do allozteric enzymes exhibit and why

Answer 8

They exhibit sigmoidal curves and it is due to cooperative binding

Question 9

Can Vmax for allosteric enzymes be altered?

Answer 9

Yes, Vmax can be altered depending on if an effector is bound and if it is activating or inhibiting

Question 10

Can the affinity of an allosteric enzyme for a substrate (K0.5) be altered?

Answer 10

Yes, K0.5 can be altered depending on if an effector is bound and if it is activating or inhibiting

Question 11

Result of activators on allosteric enzymes regarding K0.5 and Vmax

Answer 11

• K0.5 decreases (increased affinity)

* Vmax increases (more S can be reacted with)

Question 12

Result of inhibitors on allosteric enzymes regarding K0.5 and Vmax

Answer 12

• K0.5 increases (decreased affinity)

* Vmax decreases (less S can be reacted with)

Question 13

What type of effect does isoleucine (endproduct) have on threonine deaminase?

Answer 13

Isoleucine is feedback inhibiting threonine deaminase

Question 14

What are the effectors of Aspartate Transcarbamoylase (ATCase)?

Answer 14

ATP and CTP

Question 15

Which ATCase effector is the inhibitor, which state is ATCase in, and what type of relationship are they demonstrating?

Answer 15

• CTP
• T-state
• Feedback inhibition

Question 16

Which ATCase effector is the activator, which state is ATCase in when bound to it, and what type of relationship are they demonstrating?

Answer 16

• ATP
• R-state
• Feed forward

Question 17

Allosteric concerted model

Answer 17

The effector binds inducing conformational changes in the rest of the subunits of the protein

Question 18

Allosteric sequential model

Answer 18

The effector binds one subunit making the neighboring subunits more susceptible to change (similar to Hemeglobin)

Question 19

Allosteric regulation model: Modulation

Answer 19

The effector binds, inducing a conformational change that creates a binding site that wasn’t there before.

Question 20

Allosteric regulation model: Fusion

Answer 20

Effector binds causing conformational change in separate protein all together.

Question 21

Calmodulin has what effect on what enzyme?

Answer 21

Calmodulin activates Glycogen Phosphorylase (GP)

Question 22

Why does elastin breakdown in smoker’s cells

Answer 22

Methionine is oxidized on ∂1-antiproteinase, blocking it’s ability to bind and inactivate elastase. Free elastase over time destroys the lung tissue causing emphysema.

Question 23

Chemical donor and target(s) for Phosphorylation

Answer 23

ATP. Serine, Threonine, Tyrosine, and Histidine

Question 24

Chemical donor and target(s) for Adenylation

Answer 24

ATP. Tyrosine

Question 25

Chemical donor and target(s) for Uridylylation

Answer 25

UTP. Tyrosine

Question 26

Chemical donor and target(s) for ADP-Ribosylation

Answer 26

NAD. Arginine, Glutamine, Cysteine, and modified Histidine

Question 27

Chemical donor and target(s) for Methylation

Answer 27

S-Adenosyl methionine (SAM). Glutamic acid

Question 28

Explain Glycogen phosphorylase (GP) regulation

Answer 28

GP is phosphorylated by GP Kinase to become more active. GP is dephosphorylated by GP phosphatatse to become less active

Question 29

Limited Proteolysis acts via covalent or non-covalent interactions?

Answer 29

Covalent interactions

Question 30

One-time, irreversible and highly selective cleaving of a polypeptide chain by a protease

Answer 30

Limited Proteolysis

Question 31

What is the name of the precursor form of a digestiv enzyme?

Answer 31

Proenzyme or zymogen

Question 32

Limited Proteolysis acts on what type of molecules?

Answer 32

Proenzymes or zymogens to cleave them into their active form

Question 33

Explain how Chymotripsinogen becomes Chymotripsin

Answer 33

The protease trypsin cleaves chym.ogen into two fragments. The large fragment cleaves intself into two fragments and those 3 fragments covalently link to form active chymotrypsin

Question 34

Constitutive enzymes

Answer 34

Enzymes whose concentrations remain essentially constant over time

Question 35

Covalent interactions with enzymes: Modifications

Answer 35

Addition of feature to specific residues ie. Adenylation = add’n of P from ATP onto tyrosine

Question 36

The 2 ways to change enzyme abundance

Answer 36

Protein synthesis and protein degredation