Enzymes

Question 1

What is activation energy?

Answer 1

The amount of energy a reaction needs to occur

Question 2

How do enzymes lower activation energy?

Answer 2

They provide an alternative pathway for a reaction, one with a lower activation energy,

Question 3

What does lowering activation energy mean in terms of temperature?

Answer 3

Reactions can occur at lower temperatures than they would normally, this speeds up the rate of reaction.

Question 4

What are cofactors?

Answer 4

They are additional non-protein molecules that are attached to or within enzymes which allows them to function

Question 5

What are prosthetic groups?

Answer 5

They are cofactors that form part of an enzymes structure

Question 6

What is the lock and key model?

Answer 6

The active site of an enzyme is rigid and only works with substrates that are the exact fit

• A substrate with the right shape binds to form the enzyme-substrate complex
• The reaction occurs and the enzyme-product complex forms
• The products separate from the enzyme and the enzyme remains unchanged.
• This is what scientists thought when first studying enzymes

Question 7

What is the induced fit model?

Answer 7

The active site of an enzyme is not rigid, it can change shape

• A substrate that can change the shape of the active site in the right way binds
• The enzyme-substrate complex is catalysed to an enzyme-product complex by the active site
• The products leave the site and the shape of the active site returns to its original shape.
• This is the modern, accurate view on enzyme function

Question 8

Why are enzymes described as biological catalysts?

Answer 8

They speed up metabolic reactions. (Takes place in a living things) They aren’ t used up in the reaction

Question 9

What do anabolic enzymes do?

Answer 9

They build more complex molecules by combining several/lots of smaller ones

Question 10

What do catabolic enzymes do?

Answer 10

They breakdown bigger molecules into smaller ones

Question 11

Give examples of how enzymes can affect structure

Answer 11

Enzymes can affect structures such as in the production of collagen or keratin

Question 12

Give examples of how enzymes can affect functions

Answer 12

Enzymes can affect functions in a cell such as respiration, photosynthesis and DNA
replication.

Question 13

Describe the structure of enzymes

Answer 13

• Globular proteins
• Enzymes have an active site with a specific shape that substrate molecules bind to
• The tertiary structure dictates the shape of the active site
• The shape of the substrate is complementary to the active site

Question 14

Give an example of an enzyme that catalyses intracellular reactions

Answer 14

• Catalase - breaks down hydrogen peroxide into water and oxygen.
• Hydrogen peroxide is a toxic by-product of several metabolic processes. If it builds up it can kill
  cells and tissues.

Question 15

Give two examples of enzymes that catalyse cellular reactions

Answer 15

• Amylase catalyses breakdown of starch into maltose.. its found in saliva, secreted into the mouth by the salivary glands, as the first chemical step of digestion.
  it can also be secreted by the pancreas into the small intestine
• Trypsin catalyses the breakdown of peptide bonds. its produced by the pancreas and secreted into the small intestine to help digest proteins.

Question 16

Give an example of a cofactor for an enzyme

Answer 16

Cl- is a cofactor for the enzyme amylase which is involved in the breakdown of starch

Question 17

Give an example of a prosthetic group for an enzyme

Answer 17

Zn2+ for carbonic anhydrase which turns carbon dioxide into carbonic acid in the blood

Question 18

Give an example of a source of coenzymes

Answer 18

vitamins

Question 19

What are coenzymes?

Answer 19

A type of cofactor that form temporary associations with the enzyme

Question 20

What is the effect of temperature on enzyme activity?

Answer 20

• The rate increases because there is more kinetic energy in the molecules so they move
  faster.
• Enzymes are more likely to collide with substrates and with more force/energy so enzyme substrate complexes are more likely to form
• If temperature gets too high the reaction stops because the enzymes denature.

Question 21

What is the effect of pH on enzyme activity?

Answer 21

• Enzymes have an optimum pH value that they operate fastest at.
  The closer pH is to the optimum the faster the rate of reaction
• Enzymes will denature at pH values that are significantly different from their optimum pH.

Question 22

What pH does pepsin work best at and why?

Answer 22

pH 2 because it is used in the stomach to digest protein

Question 23

What is the effect of substrate concentration on enzyme activity?

Answer 23

High substrate concentration = fast rate of reaction because there is a greater chance of a collision that form enzyme-substrate complexes.

• A saturation point will be reached at which all the enzymes are operating at full capacity – their active sites are full.

- As substrate concentration decreases
over time (as they get used up), the rate of reaction decreases over time unless more is added.

Question 24

What is the effect of enzyme concentration on enzyme activity?

Answer 24

The higher the enzyme concentration, the greater the chances of a substrate colliding with an enzyme and forming a enzyme-substrate complex, so the rate of reaction will increase.

• If the amount of substrate is low then there will be a saturation point where the rate of reaction no longer increases with enzyme concentration.

Question 25

What are competitive inhibitors?

Answer 25

inhibitiors which compete with the substrate to bind with the enzyme. When they bind, no reaction takes place.

Question 26

What are non competitive inhibitors?

Answer 26

Inhibitors which don’t compete with the substrate to bind to the enzyme. They bind to the allosteric site of an enzyme causing the active site to change shape so that no substrate can bind to it. The effect of this type of inhibition is much stronger than that of competitive inhibitors.

Question 27

what happens when inhibitors form covalent bonds with the enzyme?

Answer 27

covalent bonds are strong so this makes the reaction irreversible

Question 28

How can inhibitors be useful

Answer 28

They can be used for regulating metabolic reactions

Question 29

What happens when inhibitors form hydrogen bonds with the enzyme

Answer 29

If an inhibitor forms hydrogen bonds with an enzyme, then the reaction is reversible.
- hydrogen bonds are weaker

Question 30

Give examples of inhibitors in poisons

Answer 30

Cyanide irreversibly inhibits cytochrome c oxidase, an enzyme that catalyses reactions during respiration.
• Arsenic inhibits pyruvate dehydrogenase,
another respiratory enzyme

Question 31

Give examples of medicinal inhibitors

Answer 31

Antivirals
• Inhibitors of viral enzyme reverse transcriptase prevent viruses from replication, used in HIV treatment Antibiotics
• Penicillin inhibits transpeptidase, preventing
bacteria from growing their cell walls and
ultimately killing them.