Enzyme Regulation

Question 1

Two general ways to handle when an enzyme has more than one substrate

Answer 1

Ternary Complex and Ping Pong

Question 2

Ternary complex

Answer 2

Can either be random order binding of enzyme to either substrate, or an ordered way of binding (ie substrate one first then substrate 2, etc)

Question 3

Ping Pong

Answer 3

Ex: Substrate 1 enters, then product one, then substrate 2, etc.

Question 4

Do enzymes with two or more substrates have the same Km for each substrate?

Answer 4

No, there will be a different Km for each substrate

Question 5

Example of Ping Pong

Answer 5

hexokinase binding to glucose and ATP

Question 6

The two main classes of molecular inhibition

Answer 6

Reversible and irreversible

Question 7

Inhibitor competes with the active site and there is no catalysis. Forms an EI complex

Answer 7

Competitive inhibition

Question 8

Inhibitor binds to a spot other than the active site which renders the enzyme inactive. Forms an ESI complex

Answer 8

Uncompetitive inhibition

Question 9

Inhibitor binds in spot other than the active site. Can bind either the E or ES complex but has a bias toward one. Is a true mix of the first two mechanisms

Answer 9

Mixed inhibition

Question 10

Special case of mixed inhibition where alpha = alpha’. Can bind to E or ES complex

Answer 10

Non-competitive inhibition

Question 11

Vmax stays the same (unchanged) and apparent Km increases

Answer 11

Competitive inhibition

Question 12

Vmax decreases and apparent Km decreases

Answer 12

Uncompetitive inhibition

Question 13

Vmax decreases and apparent Km stays the same

Answer 13

Non-competitive inhibition (mixed)

Question 14

Can wash out effects of inhibitor by increasing the substrate concentration

Answer 14

Competitive inhibition

Question 15

Can’t wash out effects of inhibitor by increasing the substrate concentration

Answer 15

Uncompetitive inhibitor and Noncompetitive inhibitor

Question 16

Why can’t we wash out the effects of the uncompetitive and noncompetitive inhibitor with substrate?

Answer 16

Inhibitors are not bound to the active site, so substrate is already bound where it needs to be. Inhibitor just stops reaction from occurring.

Question 17

Forms covalent bonds with the enzyme and are permanently bonded to the active site. Called suicide inhibitors

Answer 17

Irreversible inhibitors

Question 18

Examples of irreversible inhibition

Answer 18

Penicillin with penicillin binding proteins

Question 19

Why is penicillin so impressive?

Answer 19

The target enzyme of penicillin (transpeptidase) does not live in our bodies, it lives in bacteria. Because of this, when penicillin binds to bacteria to stop their function, our cells and enzymes stay the same so we are unlikely to have any side effects.

Question 20

Type of inhibition when the end product of a pathway is the molecule that shuts that pathway down.

Answer 20

Feedback inhibition

Question 21

Why is feedback inhibition important?

Answer 21

It prevents production of intermediates that the body won’t use, or intermediates that already exist in too high of quantities.

Question 22

Regulatory enzymes that have 2 different subunits. One that has an active site and one that has the regulatory site.

Answer 22

Allostery

Question 23

When binding of a molecule on one part of a protein affects the shape and behavior of the protein

Answer 23

Allosteric modulation

Question 24

Enzymes that have a modulator that is different from the substrate. It binds outside of the active site

Answer 24

Heterotropic enzymes

Question 25

When the substrate is the modulator and active site is the regulatory site

Answer 25

Homotropic enzymes

Question 26

Do allosteric enzymes follow the M-M rules?

Answer 26

No. Change in rate caused by modulator creates a sigmoidal curve. No true Km

Question 27

Homotropic enzymes have sigmoidal curves. What does that suggest?

Answer 27

Cooperativity

Question 28

For heterotrophic enzymes, which regulator could lower Km but not alter the Vmax? (Opposite is ANOTHER possibility)

Answer 28

Positive regulator

Question 29

For heterotrophic enzymes, which regulator could raise Km but not alter Vmax? (Opposite is ANOTHER possibility)

Answer 29

Negative regulator

Question 30

Examples of reversible covalent modifications

Answer 30

Methylation, ADP-ribosylation, Acetylation, Adrenylylation, Myristoylation, Prenylation, Ubiquitination, Phosphorylation

Question 31

Enzymes that add a phosphoryl group to a protein (add to Tyr, Ser, Thr)

Answer 31

Kinase

Question 32

Enzymes that remove a phosphoryl group from an enzyme

Answer 32

Phosphatase

Question 33

What does adding a phosphate group do to a protein?

Answer 33

Can cause it to be a disrupting, negatively charged “blob”, can block a binding site, can change the entire shape of the protein

Question 34

Stored form of glucose kept largely in muscle and liver. Mobilized when urgent need for glucose oxidation or when there is low nutrition. Way we store energy in our bodies, “ball of energy”

Answer 34

Glycogen

Question 35

Glucose-1-phosphate is turned into Glucose-6-phosphate which is used to enter glycolysis

Answer 35

Glycogen phosphorylase kinase

Question 36

A protease that is activated by proteolytic cleavage breaks down protein in the gut

Answer 36

Trypsin

Question 37

Pre-cursosr (pre-cleavage) trypsin in called what?

Answer 37

Trypsinogen

Question 38

Trypsinogen is a zymogen. What does that mean?

Answer 38

It is the inactive pre-cursor. Needs to be cleaved to form the active enzyme