Enzymes

Question 1

what are enzymes?

Answer 1

enzymes are globular proteins that catalyse metabolic reactions

Question 2

what are the 2 reactions under metabolic reaction? (metabolism)

Answer 2

anabolic reactions - larger molecules built from smaller molecules (e.g. amino acids becoming proteins)

catabolic reactions - larger molecules broken down

Question 3

where do enzymes come from?

Answer 3

some enzymes are secreted and work externally (extracellular enzymes)

most enzymes remain in the cells (intracellular enzymes)
found inside organelles, in the membranes of organelles, in the cytosol and in the cell surface membrane

Question 4

what is a catalyst?

Answer 4

a catalyst is a molecule that speeds up a chemical reaction but remains unchanged at the end of the reaction.

Question 5

how does a reaction occur?

Answer 5

there must be an effective collision between 2 molecules.

the molecules must collide with each other in the right way and at the right speed.

Question 6

things to note about enzymes

Answer 6

requires in small amounts
remain unchanged at the end of the reaction
specific in action
affected by temperature and pH

Question 7

what is activation energy?

Answer 7

the minimum amount of energy needed to raise molecules to a transition state

it is an energy barrier that needs to be overcome before the reaction can happen.

Question 8

what do enzymes do to the activation energy?

Answer 8

enzymes lower the activation energy needed for the molecules to react

Question 9

what does it mean by enzymes are highly specific in their action?

Answer 9

enzymes only catalyse one type of reaction or only a very small group of very similar reactions

Question 10

why are enzymes highly specific?

Answer 10

the active site where the substrate molecule binds has a precise shape and distinctive chemical properties. Only particular substrate molecules can fit to a particular active site.

Question 11

what are active sites?

Answer 11

active sites are depressions on the surface of the enzyme that fits the shape of the specific substrate molecule.

the active site has a unique 3D shape that only particular substrate molecules can fit into

Question 12

describe the lock and key hypothesis

Answer 12

in a reaction catalysed by an enzyme, the starting substance is called the substrate. It is converted to product. An enzyme works by binding to its substrate molecule at a specifically formed pocket in the enzyme.
As the enzyme and substrate form a complex, the substrate is raised in energy to a transition state and then breaks down into products plus unchanged enzymes.

Question 13

describe induced fit hypothesis

Answer 13

at the active site, arrangement of certain amino acid molecules in the enzyme exactly matches certain groupings on substrate, enabling enzyme-substrate complex to form.
As the complex is formed, an essential, critical change of shape is caused in the enzyme.
This change of shape is important in momentarily raising the substrate molecule to the transitional state, allowing a reaction to occur.

Question 14

effects of temperature on enzyme reaction (increase in rate of reaction)
*add in the name of the enzyme and substrate based on the question

Answer 14

when there is an increase in rate of reaction:
1. describe (quote exact data)
e.g. For every 10°C rise in temperature, the rate of enzymatic reaction is doubled until the optimum temperature is reached.
2. explain (memorise this!)
Enzymes are inactive at low temperatures due to low kinetic energy; the frequency of effective collision is low. As temperature increases, kinetic energy of the substrate and enzyme molecules increases, thereby increases the frequency of effective collisions between substrates and enzyme active sites, which increases the rate of formation of enzyme-substrate complex and increases the rate of reaction/products formed.

Question 15

effects of temperature on enzyme reaction (optimum temperature)
*add in the name of the enzyme and substrate based on the question

Answer 15

when rate of reaction is at its highest:
1. describe (quote exact data)
Enzyme activity is highest at its optimum temperature of 35-40°C.
2. explain (memorise!)
All enzyme active sites are occupied/saturated.

Question 16

effects of temperature on enzyme reaction (decrease in rate of reaction)
*add in the name of the enzyme and substrate based on the question

Answer 16

when rate of reaction is decreasing:
1. describe (quote exact data)
When temperature is increased beyond the optimum temperature of 40°C,
2. explain (memorise!)
high temperatures break the bonds that keep the enzyme protein in its specific shape. The active site loses its original shape and is no longer complementary to the substrate. The enzyme is denatured and loses its catalytic function.

Question 17

effects of pH on enzyme reaction (optimum pH)

*add in the name of the enzyme and substrate based on the question

Answer 17

when rate of reaction is at its highest:
1. describe (quote exact data)
e.g. Enzyme has an optimum pH of 6 in which it functions most efficiently. Rate of reaction is at a maximum of 5.
2. explain (memorise!)
Enzyme maintains its specific 3D conformation and so the enzyme active site is complementary to the substrate. Enzyme binds the substrate to form the enzyme-substrate complex. Substrate is converted to products.

Question 18

effects of pH on enzyme reaction (pH is not optimum)

*add in the name of the enzyme and substrate based on the question

Answer 18

when pH is not optimum:
1. describe (quote exact data)
e.g. A change in pH 3-4 can affect enzyme activity.
2. explain (memorise!)
Structure of the protein is maintained by various bonds. Changes in pH alter the bonding pattern, thereby altering the 3D conformation/shape of the active site of the enzyme. Hence, the substrate is no longer complementary to the active site. No enzyme-substrate complex can be formed. No product is formed. The enzyme is denatured and loses its catalytic function.