Chapter 8 - Enzymes

Question 1

Define an enzyme

Answer 1

A globular protein molecule which acts as a biological catalyst to speed up chemical reactions without itself being changed during the reaction

Question 2

Explain that every metabolic reaction is catalysed by enzymes

Answer 2

• Enzymes are responsible for every metabolic reaction
• Metabolism is the name given to all chemical reactions in living organisms
• Anabolism is larger molecules built up from smaller ones
• Catabolism is larger molecules broken down into smaller ones
• Anabolism + Catabolism = Metabolism
• Thousands of different enzymes, they catalyse only one reaction
• Cells can control the synthesis and activity of enzymes

Question 3

Name 9 properties of enzymes

Answer 3

• Made of proteins
• Biological catalysts
• Remain unchanged during reactions
• Very specific
• Can be used over and over
• In small quantities
• Affected by temperature
• Affected by pH
• Lower activation energy

Question 4

Name four factors on which the rates of activity in enzymes depend

Answer 4

• pH
• Temperature
• Concentration of enzyme
• Concentration of substrate

Question 5

Describe the structure of an enzyme

Answer 5

Enzymes are globular protein molecules consisting of long chains of amino acids in specific order and number

Question 6

Describe the primary structure of proteins

Answer 6

Long chain of amino acids held together by peptide bonds

Question 7

Describe the secondary structure of proteins

Answer 7

Different amino acids affect the folding of the chain into an alpha helix or beta pleated sheet, which is stabilised by hydrogen bonds

Question 8

Describe the tertiary structure of proteins

Answer 8

The secondary structure folds into a specific 3D shape, stabilised by disulphide, ionic and hydrogen bonds

Question 9

Describe the quaternary structure of proteins

Answer 9

Combination of more than one polypeptide or protein chain

Question 10

Explain enzyme activity in terms of the active site

Answer 10

Enzymes are very specific. The active site has a specific shape, in which only one type of substrate will fit. When the correct substrate enters the active site, it will fit and a reaction will occur. When an incorrect substrate enters the active site, it will not fit and no reaction will take place

Question 11

Define a substrate

Answer 11

A molecule or substance on which an enzyme acts

Question 12

Define an active site

Answer 12

A dent in an enzyme molecule which has exactly the correct shape for a certain substance to fit into

Question 13

Define a product

Answer 13

New molecules which leave the active site after the enzyme had acted on the substrate

Question 14

How to enzymes speed up reactions?

Answer 14

• Enzymes has active sites which make them specific
• A substrate collides with the active site
• The active site has a complimentary shape
• An induced fit occurs between the enzyme and the substrate
• An enzyme substrate complex forms
• The enzyme acts on the substrate and new molecules are released from the active site
• The enzyme remains unchanged and ready to form new enzyme-substrate complexes
• Enzymes increase the rate of reactions by lowering activation energy

Question 15

Name the enzyme and the product associated with starch

Answer 15

• amylase

- maltose

Question 16

Name the substrate and the product associated with maltase

Answer 16

• multose

- glucose

Question 17

Name the enzyme and the substrate associated with fatty acids and glycerol

Answer 17

• lipase

- lipids (fats & oils)

Question 18

Name the substrate and the product associated with sucrase

Answer 18

• sucrose

- fructose and glucose

Question 19

Name te enzyme and the product associated with proteins

Answer 19

• pepsin

- polypeptides

Question 20

name the product and substrate associated with trypsin

Answer 20

• polypeptides

- amino acids

Question 21

Explain what is meant by ‘optimum temperature’

Answer 21

The temperature at which the rate of reaction is the highest

Question 22

Explain why humans have less energy when it is cold

Answer 22

The rate of enzyme activity is slow, because the lack of kinetic energy means that there are less collisions between enzymes and substrates and less ESC’s form.

Question 23

Explain why it is dangerous to be exposed to extremely high temperatures

Answer 23

When enzymes gain too much kinetic energy, the molecules vibrate too violently and break the bonds which holds the structure together. This causes the active site to change shape, and the substrate will not be able to fit into the active site. The enzyme is then said to be denatured

Question 24

Describe the role of enzymes in the germination of seeds

Answer 24

• Seeds contain enzymes, an embrio plant and stored nutrients
• Protein, starch and lipid molecules are insoluble and cannot be used by the embrio plant unless changed by enzymes
• Enzymes become active by absorbing water during germination
• Gibberellic acid is formed in the embrio and activates the enzymes to digest insoluble nutrients into soluble nutrients
• Amylase (starch to maltose), protease (proteins to polypeptides) and lipase (lipids to fatty acids & glycerol)
• Soluble nutrients are used by the embrio for growth and respiration