Enzymes

Question 1

What are enzymes?

Answer 1

Biological catalysts that are globular process which lower activation energy causing reactions to occur at much faster rates

Question 2

What are anabolic reactions?

Answer 2

The building up of large molecules from small molecules

Question 3

What are catabolic reactions?

Answer 3

The breaking down of large molecules into smaller ones

Question 4

What is metabolism?

Answer 4

The sum of all reactions and reaction pathways within a cell or organism

Question 5

What is Vmax?

Answer 5

The maximum initial velocity or rate of enzyme catalysed reaction. The maximum rate of reaction of an enzyme

Question 6

Explain the lock and key hypothesis

Answer 6

Specific substrate will fit the active site of one specific enzyme

Question 7

What happens when an active site is bound to a substrate in the lock and key hypothesis?

Answer 7

Enzyme substrate complex is formed
Substrate and active site form temporary bonds between R groups (puts strain on bonds in the substrate)
Enzyme product complex formed

Question 8

What does the induced fit hypothesis state?

Answer 8

Active site of enzyme slightly changes as substrate enters.

Question 9

Explain, in terms of bonds, what happens during the induced fit hypothesis

Answer 9

Intitial interaction=weak
Enzymes tertiary structure strengthens bonding
Puts strain on bonds inside molecule, then weakens them
Lowers activation energy

Question 10

What are intracellular enzymes?

Answer 10

Enzymes that work within cells

Question 11

Give an example of an intracellular enzyme and what it breaks down

Answer 11

Catalase- breaks down hydrogen peroxide

Question 12

What are extracellular enzymes?

Answer 12

Enzymes that work outside the cells they are produced in

Question 13

Give 2 examples of extracellular enzymes and explain what they do

Answer 13

Amylase and Trypsin, break down the large molecules into smaller molecules so that they can be absorbed in the bloodstream and through cell membranes

Question 14

Explain the process of starch digestion

Answer 14

1) Starch broken down into maltose via amylase in saliva and small intestine
2) Maltose is broken down into glucose via maltase in the small intestine
3) Glucose is absorbed into the cells in digestive system

Question 15

What is trypsin and what is its role?

Answer 15

A protease that catalyses digestion of proteins

Produced in the pancreas, passes into small intestine in pancreatic juice

Question 16

What does an increase in temperature do to enzyme activity? (not including too high temperatures that cause denaturation)

Answer 16

Increases kinetic energy of particles
More frequent collisions
More frequent successful collisions between enzyme and substrate
Increased rate of reaction

Question 17

What is the temperature coefficient of a reaction?

Answer 17

A measure of how much the rate of reaction increases with a 10 C increase in temperature

Question 18

What is the temperature coefficient for enzyme controlled reactions?

Answer 18

2

Question 19

Explain how an enzyme becomes denatured by temperature in terms of bonds

Answer 19

Higher temperatures-bonds holding the protein together vibrate more
Vibrations increase
Bonds strain
Bonds break
Change in precise tertiary structure- conformational change

Question 20

Why can an enzyme no longer react when it has been denatured?

Answer 20

Active site changes shape and is no longer complementary to substrate. Can’t bind. No function

Question 21

How are enzymes adapted to cold environments?

Answer 21

Flexible structures, specifically active site

Question 22

How are enzymes present in thermophiles adapted?

Answer 22

More stable due to increased number of bonds (hydrogen and disulfide bridges) in tertiary structures

Question 23

What is renaturation?

Answer 23

When pH changes from optimum temperatures the enzyme is denatured, however if pH returns to optimum levels the enzyme returns to original shape

Question 24

What happens to tertiary structure of an enzyme at low pH?

Answer 24

Less R groups are able to interact
Bonds break
Shape of enzyme changes- conformational change

Question 25

What happens to tertiary structure of an enzyme at high pH?

Answer 25

R groups interact more
Bonds form
Shape of enzyme changes- conformational change

Question 26

What happens when substrate concentration increases?

Answer 26

Increased collision rate
More E-S complexes forming
Rate of Reaction increases

Question 27

What happens to enzyme activity at Vmax?

Answer 27

All active sites are occupied by substrate molecules
No E-S complexes can be formed
Other factors affecting rate of reaction

Question 28

What are inhibitors?

Answer 28

Molecules that prevent/slow down enzyme carrying out normal function of catalysis

Question 29

What happens during competitive inhibition?

Answer 29

A molecule has similar shape to substrate so has complementary shape to active site
Blocks substrate from entering active site
Enzyme can’t catalyse reaction as fast as it is inhibited

Question 30

Explain effect of competitive inhibition on rate of reaction

Answer 30

Reduces rate of reaction but substance still reaches Vmax

Question 31

What does the degree of competitive inhibition depend on?

Answer 31

Substrate, enzyme and inhibitor concentration

Question 32

Give 2 examples of competitive inhibitors and what they do

Answer 32

Statins- synthesise cholesterol

Aspirin- irreversibly inhibits the active site of COX enzymes preventing synthesis of prostaglandins and thromboxane

Question 33

Explain how non-competitive inhibitors work

Answer 33

Inhibitor binds to allosteric site
Causes conformational change in tertiary structure
Active site no longer complementary to substrate
Enzyme can’t carry out function

Question 34

What effect does non-competitive inhibition have on rate of reaction and Vmax?

Answer 34

Cannot reach Vmax
Rate of reaction decreased, increasing concentration of inhibitor slows this further however increasing concentration of enzyme won’t overcome effect

Question 35

Give 2 examples of irreversible non-competitive inhibitors

Answer 35

Organophosphates- insecticides & herbicides

Proton pump inhibitors- treat long term indigestion

Question 36

What is end-product inhibition?

Answer 36

Enzyme inhibition when product of a reaction acts as an inhibitor to the enzyme that produces it

Question 37

What type of inhibition is end product inhibition?

Answer 37

Non-competitive reversible inhibition

Question 38

Which metabolic pathway uses end-product inhibition?

Answer 38

Respiration

Question 39

What do cofactors do?

Answer 39

Help enzymes function as biological catalysts by transferring groups from one to another or forming part of the active site of an enzyme

Question 40

What are coenzymes?

Answer 40

Organic cofactors

Question 41

Where are inorganic cofactors obtained from?

Answer 41

Diet as minerals eg iron, calcium, chloride and zinc

Question 42

Where are coenzymes obtained from?

Answer 42

Vitamins

Question 43

What are prosthetic groups in terms of enzymes?

Answer 43

Cofactors which are required by certain enzymes to carry out catalytic function

Question 44

Give an example of a prosthetic group

Answer 44

Zn 2+ part of carbonic anhydrase

Question 45

What is precursor activation?

Answer 45

Enzymes released inactivated that then undergo conformational change by adding cofactor to become activated

Question 46

Give equation for precursor activation

Answer 46

Apoenzyme + Cofactor- Holoenzyme

Question 47

What is a zymogen?

Answer 47

A type of precursor activation where a change in pH or temperature causes activation of enzyme

Question 48

Give an example of a zymogen

Answer 48

Inactive pepsinogen released and activated by acid pH in the stomach