Exam 2 Lecture #2 (Enzyme Kinetics and Function)

Question 1

Draw a graph of the speed of an enzyme as a function of substrate concentration

Explain Km and Vmax

Answer 1

Vmax is the enzyme’s top speed

Km is [S] at 1/2 vmax

Km is related to affinity

low Km means high affinity for substrate

high Km means low affinity for substrate

Question 2

Draw the reaction proceedings for a competitive inhibitor. How does a competitive inhibitor work?

How can you overcome competitive inhibition?

Answer 2

Competitive inhibitor binds reversible to the enzyme, depleting the population of enzymes that are able to bind to the substrate and make product.

This has the virtual effect of reducing the amount of substrate. Increasing the amount of substrate can overcome the competitive inhibition.

Question 3

Draw the reaciton proceedings for a uncompetitive inhibitor. How does an uncompetitive inhibitor work?

Answer 3

Uncompetitive inhibition binds reversible to Enzyme Substrate complex. It does not help to increase the amount of substrate because inhibitor binds to ES.

Question 4

Draw the reaction pathway for a mixed inhibitor. What does a mixed inhibitor do? What is a noncompetitive inhibitor?

Answer 4

Mixed inhibitor: inhibitor binds reversibly to enzyme AND enzyme substrate complex. The EI complex can also bind substrate and produce product, but at a slower rate.

A special example of mixed inhibition is a “noncompetitive inhibitor.” This binds equally well to both E and ES. This has the virtual effect of reducint the amount of enzyme.

Question 5

Draw the Linweaver Burkplot for a Competitive Inhibor. What does a competative inhibitor do to Km and Vmax?

Answer 5

Competitive inhibitor increases Km. No change to vmax.

Question 6

Draw the linweaver burkplot for an uncompetitive inhibitor. What does an uncompetitive inhibitor do to Km and Vmax?

Answer 6

Uncompetitive inhibitor: Decrease Km, Decrease Vmax

Question 7

Draw the lineweaver burk plot for a noncompetitive inhibitor. What happens to Km and Vmax?

Answer 7

Noncompetitive Inhibitor: Vmax DECREASES, no change in Km

Question 8

Draw the normal plot (enzyme velocity as a function of [S]) for the effects of a competitive inhibitor?

Answer 8

Competitive Inhibitor: Increase Km (reduces apparent affinity for substrate)

NO change in vmax

Question 9

Draw a normal plot (velocity of enzyme as a function of [S]) for uncompetitive inhibition.

Answer 9

Uncompetitive inhibition: decreases both Km and Vmax

Question 10

Draw a normal plot (enzyme velocity as a function of [S]) for noncompetitive inhibition.

Answer 10

Noncompetitive inhibition: decreases Vmax without changing Km

Question 11

Explain what cooperativity means.

Answer 11

Cooperativity: Substrate binding increases the affinity for binding of more substrate

This can be due to multiple binding sites on the enzyme or multiple enzymes in a complex that interact with each other.

Question 12

For Cooperativity and Hill’s coeffecient, what does it mean when Hill’s coeffecient = 1

Answer 12

Hill’s = 1 means NO COOPERATIVITY

Question 13

What happens to cooperativity when Hill’s coeffectient is GREATER than 1

Answer 13

Hill’s coeffecient greater than one (example Hill’s = 2) means positive cooperativity.

Question 14

What happens to cooperativity when Hill’s coeffecient is LESS than one

Answer 14

Hill’s < 1 means negative cooperativity

Question 15

What are five ways that enzymes can be regulated? Name the five enzyme regulation mechanisms.

Answer 15

1. covalent modification (eg. phosphorylation)
2. allosteric control (eg ATP binding to a sensor)
3. Enzyme concentration (eg gene expression increased to make more enzyme when needed)
4. Activators and Inhibitors (adenylate cyclase activated by a G protein)
5. Compartmentation (eg translocation of kinase to a specific target site to increase its effective activity and selectivity)

Question 16

Explain how enzymes can be used as drug targets

Answer 16

Enzyme’s as drug targets:

Sildenafil aka VIAGRA was originally desinged to treat hypertension but is now used to treat erectile dysfunction.

Question 17

Enzymes can also be used as assay markers. Given an example

Answer 17

Enzymes as assay markers: Assay for creatine kinase as an indicator of muscle damage

Question 18

Enzymes can alter clearance rates for drugs. Give two examples

Answer 18

CYPE1 is an enzyme that converts acetamenophen and alcohol into waste products. This is why alcoholics cannot take tylenol because the breakdown of too much of both can create toxic products.

Also, there is an enzyme called aldehyde dehydrogenase. It breaks down alcohol into acetaldehyde and then to acetic acid. in 20% of asians, and in people who take Disulfiram (Antabuse), aldehyde dehydrogenase will be inhibited from turning acetaldehyde into acetic acid. The buildup of acetaldehyde is what creates naseua and bad side effects of alcohol.

Question 19

Explan how enzymes can be used as biochemical tools

Answer 19

One example of how enzymes can be used as biochemical tools is a pregnancy test. The pregnancy test is an Enzyme linked immunosorbent assay “ELISA”