Chapter 4 Enzymes

Question 1

What are enzymes?

Answer 1

Biological catalysts. The speed up the rate of reaction by reducing activation energy, without being used up

Question 2

Why are enzymes important?

Answer 2

Chemical reactions which sustain life need high rates of reaction
Needs harsh conditions such as high temperatures and pressures which are dangerous/ not feasible in cells
Enzymes can be used to enable these reactions to occur at high enough rates
Are needed within cells and outside of cells for the whole organism

Question 3

What are the two type of reactions enzymes are involved in?

Answer 3

Anabolic- building up
Catabolic- breaking down

Question 4

Define metabolism

Answer 4

The sum of all the different reactions and reaction pathways happening in a cell, which are controlled by enzymes

Question 5

How far can enzymes speed up the rate of reaction?

Answer 5

Vmax
Maximum initial velocity

Question 6

State the two explanations of enzyme action

Answer 6

Lock and Key hypothesis
Induced Fit Hypothesis

Question 7

What is the active site of an enzyme?

Answer 7

An area within the tertiary structure of an enzyme which is complimentary to the shape of a specific substrate molecule

Question 8

According to the lock and key hypothesis, what happens between the enzyme and substrate?

Answer 8

The correct substrate collides with the active site of an enzyme, forming an enzyme substrate complex
The substrate reacts to form the products, forming a enzyme product complex
The products are then released

Question 9

What does the lock and key hypothesis state?

Answer 9

Only a very specific substrate, with a shape complementary to the active site, will be able to fit in the active site of an enzyme
An enzyme will only be able to catalyse one type of very specific reaction

Question 10

According to the induced fit hypothesis, what happens between the enzyme and substrate?

Answer 10

As the substrate approaches the active site of the enzyme, hydrogen bonds will form between the two, causing a change in the tertiary structure of the enzyme= catalytic conformation
This strengthened binding weakens bonds in the reactants
The active site is now active, forming E.S.C and E.P.C releasing the products
The active site then changes back to its original inactive form

Question 11

How do enzymes reduce the activation energy?

Answer 11

May hold atoms in the substrate close enough to react together
R groups in the active site may interact with the substrate, weakening the bonds within the substrate itself

Question 12

What does catalase do?

Answer 12

Catalyses the break down of H2O2 which is a toxic product of many metabolic pathways- intracellular

Question 13

What does amylase and trypsin do?

Answer 13

Amylase digests starch (saliva, pancreas) into maltose then maltase breaks it down to glucose
Trypsin is a protease which helps break down proteins to small peptides, produced in pancreas in juice to the intestines.

Question 14

How does temperature affect enzymes?

Answer 14

Higher temperatures increases the kinetic energy of particles, making move faster so increasing collision frequency of substrate and enzyme, increasing successful collisions
More E.S.C, increased rate
If too high, bonds holding protein together vibrate more, eventually break causing change in tertiary structure=denaturing, no E.S.C

Question 15

What is Q10?

Answer 15

The temperature coefficient
A measure of how much the rate of reaction increases with a 10 degree increase, usually 2 x2 rate in enzymes

Question 16

How does pH affect enzyme activity?

Answer 16

Disrupt the ionic/hydrogen/polar bonds present in the tertiary structure of the enzyme, interact too little , therefore changing the shape of the active site (also H bonds when substrate approach disrupted)
Narrow range of pH, can renature if H+ change removed

Question 17

How does substrate concentration affect enzyme activity?

Answer 17

Increases until a point. More crowded, increase collision rate, increases number of successful collisions , more E.S.C formed, greater rate
However, at Vmax, not enough enzymes as all being used up so cannot go higher

Question 18

How does enzyme concentration affect enzyme activity?

Answer 18

Increases until a point. More crowded, increase collision rate, more E.S.C formed, greater rate
However, at Vmax, no more substrate as all being used up so cannot go higher

Question 19

What are inhibitors and what are the 2 main types?

Answer 19

Molecules which prevent enzymes from carrying out their normal function
Competitive and Non-competitive

Question 20

How does competitive inhibition work?

Answer 20

The inhibitor, a molecule which has a similar shape to the substrate, binds to active site of the enzyme , blocking the substrate from entering
Prevents catalysis, reduces the number of E.S.C in a given time
Can be permanent but usually temporary

Question 21

How does non competitive inhibition work?

Answer 21

Inhibitor binds to the enzyme not at the active site but at the allosteric site
This binding causes a change in the tertiary structure of the enzyme, active site no longer complimentary to the substrate so no E.S.C
Can be permanent or temporary

Question 22

What is an example of competitive inhibition?

Answer 22

Statins, bind to enzyme which produces cholesterol, reversible
Aspirin, binds to COX enzymes, preventing formation of chemicals which give fevers and pain, irreversible

Question 23

What is an example of non competitive inhibition?

Answer 23

Organophosphates bind to acetyl cholinesterase, prevent nerve impulses, irreversible
Used in pesticides

Proton Pump Inhibitors PPIs, block H+ in stomach, irreversible

Question 24

How do competitive and non competitive inhibitors effect vmax?

Answer 24

As substrate concentration increases:
Co. Reach original vmax but later (so much substrate is overcomes it)
Non-co. Does not reach Vmax, lower

Question 25

What is end product inhibition? Give an example

Answer 25

Products of a reaction acts as an inhibitor to the enzyme, negative feedback, prevents excess products, reduces waste to materials
e.g ATP inhibits PFK enzyme during metabolism

Question 26

What are cofactors and coenzymes? What is the difference between them?

Answer 26

Non-protein helper which helps the enzyme carry out their function
Cofactors= Inorganic Coenzymes=Organic

Question 27

Where are cofactors and coenzymes sourced? Give examples

Answer 27

Cofactors come from minerals via the diet. e.g Amylase requires a chloride ion
Coenzymes come from vitamins via the diet e.g Vit.B5 makes coenzyme A, breakdown fatty acids

Question 28

What are prosthetic groups?

Answer 28

Cofactors which are permanently bound to an enzyme
e.g Zn2+ for carbonic anhydrase, needed for CO2 breakdown

Question 29

What is precursor activation?

Answer 29

Inactive enzymes which become active by addition of a cofactor/co enzyme or certain temperatures/pH

Question 30

What are some general improvements to enzyme practicals?

Answer 30

Controlling other factors to prevent others interfering with rate- temperature, pH buffers, enzyme concentration and substrate

Adding in controls for comparison

Smaller time intervals, concentration intervals, pH, whatever is the independent, temperature intervals

Standardising- e.g same orientation of film

More precise- not a few drops, certain volume

Question 31

How does increasing enzyme concentration affect rate?

Answer 31

At first, increases rate. More enzymes in the same volume, increases the number of successful collisions, increased e.s.c, increased products
But then plateaus as all substrate in an enzyme, no more substrate, substrate concentration limiting factor

Question 32

How does temperature affect enzyme activity?

Answer 32

Low temperates, low KE, low movement, few successful enzyme substrate collisions, few E.S.C, low enzyme activity
High temperatures, high ke, high speeds, more successful collisions, for e.s.c, high enzyme activity
Until denaturing when bonds in tertiary structure break, altering active site, preventing e.s.c forming

Question 33

Why do we take out samples to check pH rather than leaving in test tube?

Answer 33

Could contaminate and affect rate
Easier to see colour behind a white tile

Question 34

What are reproducibility and repeatability?

Answer 34

Reproducibility assesses whether another person could carry out the experiment and gain the same results- of the whole practical
Repeatability assesses whether you can achieve the same results again, how repeatable the results are

Question 35

How can enzymes be made more efficient with a compound?

Answer 35

Removal of inhibitors
If needs energy, providing oxygen or glucose
If needing a certain pH, adjusting H+ ions

Question 36

What is the cofactor for amylase?

Answer 36

Chloride ions

Question 37

What is the prosthetic group for carbonic anhydrase?

Answer 37

Zn 2+

Question 38

How do serial dilutions work?

Answer 38

Standard concentration from bottle e.g 1 mol

Add 9cm3 of water to a test tube. Add 1 cm3 of 1 molar to the tube. Overall 1/10, 0.1 molar

Add 9cm3 to another test tube. Take 1 cm3 from the first. 1/10 x 0.1 molar. So 0.01 molar.

Repeat. Can vary amounts e.g 5cm3 water and 5 from previous to half each time.

Question 39

Are anabolic reactions endo or exothermic?

Answer 39

Anabolic are endothermic
Catabolic are exothermic

Question 40

When you discuss temperature and enzymes, what two aspects do you need to talk about?

Answer 40

Low temps, low rates… reversible
High temps, increased rate then dentature, sometimes reversible

Question 41

What is the name for an inactive enzyme? What is the name of the active enzyme? In precursor activation

Answer 41

Inactive- apoenzyme
Active- holoenzyme

Question 42

What are zymogens/proenzymes?

Answer 42

A type of precursor enzyme which become activated by a change in temperature or pH

Question 43

What control should be used in an enzyme practical?

Answer 43

Boiled/denatured enzyme of same volume and conc, with the same vol of buffer/temp/substrate conc