M5 - Lesson 3: Enzyme Activity and Inhibition

Question 1

The substrate must fit into the active site the way a key fits into a lock. With the substrate at, the active site, a chemical reaction occurs that involves breaking or forming bonds of the substrate.

Answer 1

Lock-And-Key Model

Question 2

What are the two modes of enzyme activity?

Answer 2

Lock-And-Key Model

Induced-fit Theory

Question 3

The substrate induces the active site to take on a shape complementary to the shape of the substrate molecule.

Answer 3

Induced-fit Theory

Question 4

The products that form are no longer attracted to the active site and leave the enzyme. The enzyme goes on to catalyze the same reaction with other substrate molecules.

Answer 4

Lock-And-Key Model

Question 5

What are the two ways of Lock-And-Key Model Hypothesis?

Answer 5

Structurally - substrates that don’t fit won’t react;

Chemically - substrates that are not chemically attracted to the active site won’t be able to react.

Question 6

The substrate may induce the enzyme to take on a shape that matches the substrate.

Answer 6

Induced-fit Theory

Question 7

What are the induced-fit model that is better explains enzyme activity?

Answer 7

Attraction
Reaction (conformational change)
Release (enzyme reverts to original shape)

Question 8

Formation of an enzyme-substrate complex as an intermediate species provides an alternative pathway, with lower activation energy, through which a reaction can occur.

Answer 8

The Mechanism of Enzyme Action

Question 9

The active site has a fixed geometric shape. Only a substrate with a matching shape can fit into it.

Answer 9

Lock-and-Key Model

Question 10

The active site has a flexible shape that can change to accept a variety of related substrates. Enzymes vary in their degree of specificity for substrates.

Answer 10

Induced-Fit Model

Question 11

The action of many poison and drugs is due to their ability to inhibit specific enzymes.

Answer 11

Inhibition of Enzyme Activity

Question 12

Type of inhibition in which a substrate and an inhibitor compete for the active site on the enzyme. They are so similar in structure that the enzyme binds to the inhibitor by mistake.

Answer 12

Reversible Competitive Inhibiton

Question 13

As long as the competitive inhibitor occupies the active site, no reaction of the substrate can take place.

Answer 13

Reversible Competitive Inhibiton

Question 14

TRUE OR FALSE
However, we can reverse non-competitive inhibition by adding more substrate that competes with the inhibitors for the active site, The addition of large amounts of substrate can completely reverse the inhibition.

Answer 14

FALSE

reverse competitive inhibition

Question 15

• Has a structure similar to substrate
• Occupies active site
• Competes with substrate for active site
• Has effect reversed by increasing substrate concentration

Answer 15

A competitive inhibitor

Question 16

Example of competitve inhibition

Answer 16

Overcoming Alcoholism

Question 17

It interfere with active site of enzyme so substrate cannot bind

Answer 17

Competitive Inhibition

Question 18

It changes shape of enzyme so it cannot bind to substrate

Answer 18

Non-competitive Inhibition

Question 19

An inhibitor that won’t fit;

Allosteric site causing a conformational change in the active site; the substrate cannot attach to react

Answer 19

Non-competitve

Question 20

An inhibitor that is blocked;

Active site and prevents the substrate from entering

Answer 20

Competitive

Question 21

it competes with aldehyde oxidase and prevents the acetaldehyde from being converted to acetic acid

Answer 21

Antabuse (disulfiram)

Question 22

Resulting in a strong feeling of nausea and other strong hangover symptoms - a good detergent from drinking.

Answer 22

Acetaldehyde

Question 23

Administered as a daily pill, so its efficacy relies on the patients motivation.

Answer 23

Antabuse

Question 24

What are the other examples of competitive inhibition?

Answer 24

a. Ethanol as antidote in Methanol Poisoning

b. Antihistamines

Question 25

Type of inhibition wherein it binds to enzyme, at a site other than the active site. Its structure does not resemble that of the structure. When attaches to an enzyme, it alters the three-dimensional structure of the enzyme as well as the shape of the active site.

Answer 25

Reversible Non-Competitive Inhibiton

Question 26

It does not compete for the active site, adding more substrate will no reverse inhibiton.

Answer 26

Reversible Non-Competitive Inhibiton

Question 27

* Does not have a structure like substrate * Binds to the enzyme but not active site * Changes the shape of enzyme and active site * Substrate cannot fit altered active site * No reaction occurs * Effect is not reversed by adding substrate

Answer 27

A noncompetitive inhibitor

Question 28

Inhibits the enzymes that forms cells walls of bacteria, destroying the bacterium.

Answer 28

Penincilin

Question 29

Causes blood vessels to narrow, increasing blood pressure.

Answer 29

ACE

Question 30

What is the meaning of ACE?

Answer 30

Angiotensin-Converting Enzyme

Question 31

Inhibitors are given to those with high blood pressure to prevent ACE’s synthesis from its zymogen.

Answer 31

ACE (Angiotensin-Converting Enzyme)

Question 32

Protease is an essential enzyme that allows the virus to make copies of itself

Answer 32

HIV

Question 33

Protease inhibitors interfere with this copying, decreasing the virus population in the patient.

Answer 33

HIV

Question 34

A type of inhibition of enzyme activity which occurs when a functional group in the active site or a co factor required for the activity of the enzyme is destroyed or modified.

Answer 34

Irreversible Inhibition

Question 35

This is also a non-competitive inhibition; does not have a structure similar to the substrate; cannot be removed from the protein without destroying it.

Answer 35

Irreversible Inhibition

Question 36

What are the 3 Examples of Irreversible Inhibition?

Answer 36

Nerve Gases Poisoning of Heavy Metals (Hg, Pb, Ag) Penincillin

Question 37

An enzyme that catalyzes a reactions taking place at the juncture of nerve cells and also necessary for normal transmission of nerve impulses

Answer 37

Cholinesterase

Question 38

Occurs naturally in poisons and venoms; combine with the -OH group on a serine molecule that is vital to the active site of the cholinesterase enzyme. When this happens, the enzyme loses its ability to transmit nerve impulses. That is why animals poisoned by nerve gases become paralyzed.

Answer 38

Nerve Gases

Question 39

These are toxic because they bind irreversibly with free -SH functional groups on enzymes.

Answer 39

Poisoning of Heavy Metals (Hg, Pb, Ag)

Question 40

Is an antibiotic that kills bacteria because it irreversibly binds to glycopeptide transpeptidase for the synthesis of a bacterial cell wall.

Answer 40

Penincillin