enzymes

Question 1

describe/define enzymes

Answer 1

protein molecules which act as biological catalysts. they greatly increase the rate of a chemical reaction without themselves being changed at the end of reaction

Question 2

how to enzymes help metabolic reactions?

Answer 2

they are enabled to proceed rapidly but at low temperatures

Question 3

what are the properties of enzymes?

Answer 3

1. are proteins
2. have active sites with a specific shape where the reaction take place
3. effective in small amounts
4. remain chemically unaltered at end of reaction
5. function by lowering activation energy required for reaction to occur
6. high degree of specificity

Question 4

what is meant by a high degree of specificity? why do enzymes have this?

Answer 4

enzymes can be specific to one type of substrate molecule or a group of substrates with similar shapes.
the specifity of an enzyme is due to conformation at active site

Question 5

how can the activity of an ezyme be changed? what is its implication?

Answer 5

it can be changed by the presence of inhibitors and activators. this implies that the rate of product formation can be controlled according to needs of the cell

Question 6

describe the general structure of an enzyme molecule

Answer 6

• complex globular shape and are relatively large molecules
• only the active site of the enzyme comes into direct contact with the substrate
• the shape of active site is complementary to shape of substrate

Question 7

define activation energy

Answer 7

the energy required to make substances react

Question 8

describe the Lock-and-Key hypothesis

Answer 8

1. active site has a specific shape, to which the substrate binds
2. the substrate is the “key”, whose shape is complementary to the shape of enzyme active site, which is the “lock”
3. ‼ the shape of substrate(s) is complementary and fits exactly into shape of active site to form the enzyme-substrate complex
4. once reaction is completed, the products are no longer complementary in shape and hence do not fit into active site, and leave the active site.

Question 9

describe the Induced Fit hypothesis

Answer 9

1. some enzymes and their active sites are physically flexible
2. ‼ the shape of substrate(s) is complementary and does not fit exactly into shape of active site
3. binding of substrate to active site induces a small conformational change in the shape of enzyme
4. the substrate fits more snugly into active site to form enzyme-substrate complex, allowing the enzyme to perform catalytic function more effectively
5. once reaction is completed, the products are no longer complementary in shape and hence do not fit into active site, and leave the active site.

Question 10

describe how enzymes work at molecular level

Answer 10

1. collision between enzyme and substrate at correct orientation causes substrate to bind to enzyme at its active site to form a short-lived enzyme-substrate complex
2. within the complex, the chances of reaction occuring is greatly increased
3. the reaction hence occurs
4. once the reaction completes, the products formed and the unchanged enzyme molecule are released
5. the enzyme is then able to catalyse another reaction

Question 11

explain what happens when enzyme denatures

Answer 11

the enzyme unfolds and the precise shape is lost, so the conformation of the active site changes.
substrate cannot bind to the active site as its conformation is no longer complementary to the shape of substrate, and so the frequency of effective collision between substrate and enzyme molecules will decrease
(this process is usually irreversible)

adapted from 2023 EOY paper

Question 12

state the typical range of optimum temperatures for mammalian enzymes

Answer 12

30-40°C

Question 13

state the effect of increase of temperature up till optimum temperature on enzymes

Answer 13

as temperature increases, the kinetic energy of the enzyme and substrate molecules increases
the frequency of effective collisions between enzyme and substrate molecules increases
more enzyme-substrate complexes are formed per unit time

Question 14

state the effect of optimum temperature on enzymes

Answer 14

at optimum temperature, enzyme functions at its maximum rate
the kinetic energy of enzyme and substrate molecules is the most ideal, resulting in highest frequency of effective collisions between enzyme and substrate molecules,
most enzyme-substrate complexes are formed per unit time

Question 15

state the effect of temperature beyond optimum on enzymes

Answer 15

excess heat disrupts the intramolecular bonds which stabilise the structures of the enzyme
the enzyme denatures
the enzyme unfolds and the precise shape is lost, so the conformation of the active site changes.
substrate cannot bind to the active site as its conformation is no longer complementary to the active site, and so the frequency of effective collision between substrate and enzyme molecules will decrease

same ending explanation as before

Question 16

state the effect of freezing temperatures on enzymes

Answer 16

enzymes are inactivated
enzyme activity is low due to less kinetic energy
lower frequency of effective collision between substrate and enzyme molecules to form enzyme-substrate complexes

Question 17

describe the effect of optimum pH on enzymes

Answer 17

at optimum pH, enzyme functions at its maximum rate
the intramolecular bonds maintaining the protein structure of enzyme are intact
conformation of active site is most ideal for substrate binding
hence highest frequency of effective collision between enzyme and substrate molecules
greater number of enzyme substrate molecules formed per unit time

Question 18

describe the effect of pH higher or lower than optimum on enzymes

Answer 18

the H+ concentration changes
the intramolecular bonds maintaining the protein structure of enzyme are altered
the enzyme denatures
the enzyme unfolds and the precise shape is lost, so the conformation of the active site changes. substrate cannot bind to the active site as its conformation is no longer complementary to the active site, and so the frequency of effective collision between substrate and enzyme molecules will decrease

(within a certain range, this is reversible. at extreme pH changes, the conformation will be severely altered)

same ending explanation as before

Question 19

describe the effect of substrate concentration on enzymes

Answer 19

for a fixed enzyme concentration, rate of enzyme reaction increases with increasing substrate concentration
an increase in number of substrate molecules leads to an increase in frequency of effective collision between enzyme and substrate molecules
more enzyme-substrate complexes formed per unit time
rate of reaction increases
the rate of reaction is limited by substrate concentration.

there is a point where further increase in substrate concentration does not significantly change the rate of reaction
because all active sites of all enzyme molecules are saturated with substrate molecules
any free substrate molecules has to wait until enzyme-substrate complexes have released its products before it can enter the active site of enzyme itself
the rate of reaction is now limited by enzyme concentration.

Question 20

describe the effect of enzyme concentration on enzymes

Answer 20

for a fixed substrate concentration, rate of enzyme reaction increases with increasing enzyme concentration
an increase in number of enzyme molecules leads to an increase in frequency of effective collision between enzyme and substrate molecules
more enzyme-substrate complexes formed per unit time
rate of reaction increases
the rate of reaction is limited by enzyme concentration.

there is a point where further increase in enzyme concentration does not significantly change the rate of reaction
as the rate of reaction is now limited by enzyme concentration.

Question 21

sketch the graphs of the effects of:
1. temperature
2. pH
3. [substrate]
4. [enzyme]

Answer 21

answer