Enzymes

Question 1

What is the Michalis-Menten Model?

Answer 1

E + S ES –> E + P

V₀ = V_max [S]o / K_m + [S]o

K_m = [S] where v_i = 1/2 V_max

Question 2

Why does Hexokinase have a low Km?

Answer 2

It will always work at Vmax, ensuring the RBC always has enough energy.

Question 3

What do enzymes do?

Answer 3

They lower the activation energy to make the forward/backward reaction happen faster.

Question 4

What are Irreversible Inhibitors?

Answer 4

The enzyme inhibitor binds so tightly, or covalently, the interaction is irreversible.

Question 5

What happens to the graph in uncompetitive inhibition?

Answer 5

Shifts left. Km goes down and takes less substrate to reach Vmax (also decreases)

Question 6

Which way will a negative allosteric effector shift the curve?

Answer 6

To the right

Question 7

What does Vmax mean?

Answer 7

describes the maximal rate at which substrate can be converted to product when the enzyme is saturated

Question 8

How can competitive inhibitors be reversed?

Answer 8

by increasing the substrate concentration.

Question 9

What does a homoallosteric curve look like? Why?

Answer 9

Sigmoidal because molecules become more attracted to enzyme as they bind. (Positive homotropic)

Question 10

What are heteroallosteric enzymes?

Answer 10

activator binds to the allosteric site to bring in the substrate for that enzyme

Question 11

What happens to the graph in uncompetitive inhibition?

Answer 11

Shifts left. Km goes down and takes less substrate to reach Vmax.

Question 12

What are allosteric enzymes? Allosteric = ?

Answer 12

these enzymes adopt different conformations in response to binding their substrates and allosteric modulators (effectors) = other shapes

Question 13

What is Km? Low Km? High Km?

Answer 13

It refers to the affinity of the sub to the enzyme. Low Km = high affinity. High Km = low affinity.

Question 14

Do enzymes work without cofactors?

Answer 14

No, without cofactors they are called apoenzymes

Question 15

What do protein kinases do? Are they specific or non-specific?

Answer 15

Phosphorylate and activate or inactivate regulatory proteins. Could be either.

Question 16

In competitive inhibition, When we add more substrate will Km increase or decrease? What about Vmax?

Answer 16

Increase, as more sub is added, graph shifts to the right. Vmax stays the same.

Question 17

What are enzyme inhibitors?

Answer 17

Substances that interact with an enzyme and reduce the rate of the enzyme-catalyzed reaction.

Question 18

Where is hexokinase found?

Answer 18

Present in all tissues except the liver and B cells of the pancreas

Question 19

What is competitive inhibition?

Answer 19

Inhibitors compete for the binding site of the substrate.

Question 20

Reversible Covalent Modification. Example?

Answer 20

allows for the coordinated response of several enzymes to a single signal. Phosphorylation of target proteins.

Question 21

Irreversible inhibitors

Answer 21

bind extremely tightly to the enzyme or form covalent bonds and cannot be removed.

Question 22

What is mixed (Noncompetitive) Inhibition? What will happen to Vmax/Km?

Answer 22

Inhibitor can bind to enzyme or ES complex. Vmax will decrease and effects on Km will vary.

Question 23

What is uncompetitive inhibition?

Answer 23

Inhibitors bind the ES complex and inhibit catalysis. (Leo bound to orange and mitten)

Question 24

What are homoallosteric enzymes?

Answer 24

exhibit cooperative substrate binding like Hb. (binds O2 to bring in MORE O2)

Question 25

What are isozymes?

Answer 25

Different forms of enzymes

Question 26

What does the rate of glucokinase depend on?

Answer 26

serum glucose once it reaches 5-8mM, Km is reached at 5mM

Question 27

Where is glucokinase found?

Answer 27

Hepatocytes and B cells of the pancreas

Question 28

Inactive precursors of some enzymes that are activated through hydrolysis reactions are called

Answer 28

zymogens

Question 29

What is proteolytic cleavage reffering to?

Answer 29

Allows for the synthesis of proteins in a n inactive (proprotein, proenzyme, or zymogen) form. When the protein activity is physiologically needed, the zymogen undergoes proteolytic cleavage and is activated.