BM: Enzyme Action

Question 1

What are enzymes?

Answer 1

Globular proteins that speed up chemical reactions by acting as biological catalysts.

Question 2

What are catalysts?

Answer 2

Molecules that alter the rate of reaction without undergoing permanent changes themselves.

Can be reused repeatedly and are useful in small amounts.

Question 3

What do enzymes catalyse?

At what levels do they do this?

Answer 3

Catalyse metabolic reactions - both at a cellular level (eg. respiration) and for the organism as a whole (eg. digestion in mammals).

Question 4

What can enzymes affect?

Answer 4

Structures in an organism (eg. production of collagen) and functions (like respiration).

Question 5

Enzyme action can be what?

Answer 5

Intracellular - within cells.

Extracellular - outside cells.

Question 6

What type of molecule is an enzyme?

Answer 6

A globular protein.

Question 7

What is the active site of an enzyme?

Answer 7

The part of the enzyme where the substrate molecules bind to.

It has a specific shape.

Question 8

What is activation energy?

Answer 8

The initial amount of energy required to start a chemical reaction.

Question 9

For a reaction to take place, what conditions must be satisfied?

Answer 9

• Molecules must collide with sufficient energy to alter the arrangement of their atoms.
• Free energy of products must be less than that of substrates.
• Activation energy must be overcame.

Question 10

What is free energy?

Answer 10

The energy of a system that is available to perform work.

Question 11

What is activation energy often provided as?

Answer 11

Heat

Question 12

How do enzymes speed up the rate of reaction?

Answer 12

By lowering the activation energy of the reaction it catalyses.

Question 13

What forms when a substrate fits into the active site of an enzyme?

Answer 13

An enzyme-substrate complex

Question 14

What actually lowers the activation energy of the reaction?

What are the reasons why?

Answer 14

The formation of the enzyme-substrate complex.

• If the two substrate molecules are joining, attaching to an enzyme holds them closer together, reducing repulsion making them bond more easily - less energy is required to do this.
• If catalysing a breakdown reaction, fitting into an active site puts more strain on bonds in substrate, so they break up more easily - less energy is required to do this.

Question 15

What was the early model of enzyme activity?

Answer 15

The lock and key model.

Question 16

What is the active site made up of?

What does it form?

Answer 16

Made of a relatively small number of amino acids, forming a small depression within the much larger enzyme molecule.

Question 17

How is the substrate molecule held within the active site?

Answer 17

By bonds that temporarily form between certain amino acids of the active site and groups on the substrate molecule.

Question 18

What does the induced fit model propose?

Answer 18

The active site forms as the substrate and enzyme interact.

Question 19

Explain the induced fit model:

Answer 19

• Proximity of the substrate (change in the environment) leads to a change in the enzyme that forms the functional active site - enzyme is flexible and can mould around substrate.
• As it changes shape, the enzyme puts strain on substrate molecule, distorting bonds within it and consequently lowering the activation energy of the reaction.

Question 20

Draw a diagram illustrating the induced fit model:

Answer 20

Question 21

What are the properties of an enzyme determined by?

Answer 21

The tertiary structure - which is determined by the primary structure.

Question 22

What does pH equal?

Answer 22

Log10 [H+]

Question 23

If the tertiary structure of an enzyme is altered, what will happen?

Answer 23

The shape of the active site will change, and the substrate won’t fit, an enzyme-substrate complex won’t be formed and the enzyme will no loger be able to carry out its function.

Question 24

Why are enzymes highly specific?

Answer 24

Only one substrate will fit the active site, because:

• Each enzyme has a different tertiary structure and so a different shaped active site.
• If the substrate doesn’t match the active site, an enzyme-substrate complex won’t be formed and the reaction won’t be catalysed.

Question 25

What is the primary structure of proteins determined by?

What would the consequence of a mutation in this be on the tertiary structure?

Answer 25

Determined by a gene.

If a mutation occurs in that gene, it could change the tertiary structure of the enzyme produced.