Enzyme Regulation

Question 1

Why do enzymes need to be coordinate?

Answer 1

In order to work together properly. Activity must be controlled so the reaction happens at the right rate, right time, and the right amount.

Question 2

What are the three types of enzyme regulation mechanisms?

Answer 2

Negative Feedback
Positive Feedback
Feed-Forward

Question 3

What is the most common way that enzyme activity is regulated?

Answer 3

Negative Feedback. Also knows as feedback inhibition

Question 4

How does Negative Feedback work?

Answer 4

It happens when downstream products make a previous step less likely to happen or less efficient. This is known as down-regulating.

Question 5

How does Positive Feedback work?

Answer 5

It happens when downstream product makes previous step better at converting.

Question 6

How does the Feed-Forward mechanism work?

Answer 6

It happens when an upstream compound makes a downstream enzyme better at converting downstream products.

Question 7

What does it mean for something to be upstream in a metabolic pathway?

Answer 7

It describes earlier steps in a pathway (first steps)

Question 8

What does it mean for something to be downstream in a metabolic pathway?

Answer 8

It describes later steps in a pathway (last steps)

Question 9

What does the word feedback mean in enzyme regulation mechanisms?

Answer 9

It refers to when the downstream product of a pathway reaches backwards to regulate the upstream steps.

Question 10

What is Negative Feedback good for?

Answer 10

It is good for maintaining homeostasis (balance within the body). It is extremely common in metabolism and is the default regulatory mechanism for any pathway you may encounter.

Question 11

What is a popular example of Positive Feeback?

Answer 11

Oxytocin in labor and childbirth.
Oxytocin causes uterine contractions and uterine contractions cause more oxytocin to be released which make contractions stronger. The endpoint is childbirth.

Question 12

What is an example of Positive Feedback that is also regulated by Negative Feedback?

Answer 12

Blood clot formation.

Question 13

Can enzymes have multiple active sites for the same ligand?

Answer 13

Yes, because binding at one active site can make it easier to bind at another active site.

Question 14

When speaking about enzymes, what does cooperativity mean?

Answer 14

It is the concept that it is hardest for an enzyme to bind its first ligand, and then it gets easier to bind the second.
Ex. How hemoglobin transports blood throughout the
body (first O2 molecule is hardest to bind)

Question 15

What does partial pressure of O2 stand for?

Answer 15

Oxygen concentration in the blood

Question 16

What does stronger cooperativity do to the curve on a graph.

Answer 16

It makes the curve greater (more s-like,sigmoidal)

Question 17

What does the Hill Coefficient tell us?

Answer 17

It tells us about an enzymes cooperativity with a substrate.

Question 18

What does it mean if the Hill Coefficient > 1 ?

Answer 18

There is positive cooperativity. The higher the coefficient the sharper the sigmoidal curve.

Question 19

What does it mean if the Hill Coefficient = 1 ?

Answer 19

There is no cooperativity

Question 20

What does it mean if the Hill Coefficient < 1 ?

Answer 20

There is negative cooperativity (binding the first substrate reduces the affinity for subsequent binding).

Question 21

What type of interactions are MOST enzyme-substrate interactions?

Answer 21

Non-covalent. Substrate is put in place by polarity and steric based interactions.

Question 22

What is an example of an enzyme regulation that involves making covalent modification?

Answer 22

Phosphorylation - catalyzed by kinases
Attaching a phosphate group to a protein affects the activity of the enzyme. Phosphorylation targets Serine, Threonine, and Tyrosine (In order of probability). These all have a hydroxyl (-OH) group.

Question 23

What does cleavage do?

Answer 23

Breaks covalent bonds.

Question 24

Where is the enzyme trypsin produced?

Answer 24

The pancreas.

Question 25

What are Zymogens?

Answer 25

Inactive precursor forms of enzymes. Usually end in -ogen.

Question 26

Are any covalent bonds formed between an enzyme and its substrate as the substrate enters the active site?

Answer 26

No

Question 27

What are cofactors?

Answer 27

Another chemical compound that enzymes require to be present in order for the enzyme to function.

Question 28

What are organic cofactors called?

Answer 28

Coenzymes

Question 29

What are some examples of inorganic cofactors?

Answer 29

Metal ions including:
Mg2+
Zn2+
Cu2+

Question 30

What do multivitamins contain?

Answer 30

Many cofactors and coenzymes.

Question 31

Describe coenzymes. How do they usually contribute to the function of enzymes?

Answer 31

They are often vitamins or vitamin derivatives. They often contribute to the function of enzymes by carrying functional groups from one place to another in a reaction.

Question 32

What is a popular coenzyme? What does it do?

Answer 32

Coenzyme A (CoA)
This coenzyme transfers acyl groups from one place to another.

Question 33

What are Prosthetic Groups? What is an example?

Answer 33

They are coenzymes that are tightly or covalently bonded to their enzymes.
Ex. Heme, which contains an iron ion in the center of a
porphyrin ring and attached to hemo an myoglobin

Question 34

What is a Haloenzyme?

Answer 34

Enzyme with the whole set of substances needed for it to be functional.

Question 35

What is an Apoenzyme?

Answer 35

Enzyme without the cofactors needed to function properly.

Question 36

Is FAD a coenzyme?

Answer 36

Yes

Question 37

Describe allosteric regulation.

Answer 37

It involves change in the 3D structure of an enzyme. An allosteric activator binds noncovalently to an allosteric site on an enzyme, which promotes a conformational shift that increases or decreases the enzyme’s affinity for its substrate.

Question 38

Can phosphorylation and cleavage only occur with enzymes?

Answer 38

No, they can occur with other proteins as well.

Question 39

What are covalent modification a subset of?

Answer 39

Subset of post-translational modifications of proteins.