5. Enzymes

Question 1

What are enzymes?

Answer 1

They are biological catalysts, they speed up metabolic reactions in living organisms and remain unchanged at the end of the reaction to be used again.
A small amount of catalyst can catalyse the conversion of a large number of substrate molecule into product molecules.

Question 2

What is turnover number?

Answer 2

The number of reactions that an enzyme can catalyse per second

Question 3

What is the active site?

Answer 3

An indented area on the surface of an enzyme molecule, with a shape that is complementary to the shape of the substrate molecule.

Question 4

What is the importance of active sites?

Answer 4

Its shape is complementary to the shape of the substrate molecule.
So each enzyme is highly specific in its function as it can only catalyse a reaction involving a particular substrate molecule.

Question 5

What determines the structure of an enzyme?

Answer 5

Instructions are encoded in genes in which determine the enzyme’s tertiary structure

Question 6

What does intracellular mean?

Answer 6

Inside the cell

Question 7

What does extracellular mean?

Answer 7

Outside the cell

Question 8

What are metabolic pathways?

Answer 8

A series of consecutive reactions, every step catalysed by a specific enzyme that produces a specific product. The reactants, intermediates and products are known as metabolites.

Question 9

What are catabolic metabolic pathways?

Answer 9

Where metabolites are broken down into smaller molecules and release energy.

Question 10

What are anabolic metabolic pathways?

Answer 10

Where energy is used to synthesise larger molecules from smaller ones.

Question 11

What is catalase?

Answer 11

An enzyme that protects cells from damage.
It quickly breaks down hydrogen peroxide, a potentially harmful by-product of many metabolic reactions into water and oxygen.

Question 12

What is the structure and properties of catalase?

Answer 12

It is the fastest-acting enzyme, having the highest turnover number known (6 million per second).
In eukaryotic cells it is found inside small vesicles called peroxisomes.
White blood cells also use it to kill invading microbes after they ingest them.

Question 13

How are extracellular enzymes used in the digestive system?

Answer 13

Many enzymes are secreted from cells lining the alimentary canal, into the gut lumen. There they extracellularly digest the large molecules found in food. These products are then absorbed via epithelial cells into the bloodstream to be used for growth and repair

Question 14

How are extracellular enzymes used in the mouth?

Answer 14

Amylase is produced in the salivary glands, and acts in the mouth to digest polysaccharides starch to the disaccharide maltose.

Question 15

How are extracellular enzymes used in the pancreas?

Answer 15

Trypsin is made in the pancreas and acts in the lumen of the small intestine to digests proteins into smaller peptides by hydrolysing peptide bonds.

Question 16

What are cofactors?

Answer 16

A substance that has to be present to ensure that an enzyme-catalysed reaction takes place at the appropriate rate.

Question 17

What are the different types of cofactors?

Answer 17

Prosthetic groups are part of the enzyme structure.

Ion cofactors and organic coenzymes form temporary associations with the enzyme.

Question 18

How do ion cofactors work?

Answer 18

Some act as co-substrates. They and the substrate together form the correct shape to bind to the active site of the enzyme.
Some cofactors change the charge distribution on the enzyme’s active site and make the temporary enzyme-substrate bonds easier to form.

Question 19

How do coenzymes work?

Answer 19

They bind temporarily to the active site either just before or at the same time that the substrate binds. They are chemically changed during the reaction and need to be recycled to their original state.

Question 20

What is the lock and key hypothesis?

Answer 20

The way that an enzyme catalyses a reaction.

The lock is the enzyme’s active site and the key is the substrate molecule.

Question 21

How do enzymes catalyse a reaction?

Answer 21

1) Substrate and enzyme molecules have kinetic energy and are constantly moving.
2) If a substrate molecule collides successfully with an enzyme molecule, it forms an ES complex.
3) The substrate is either built up or broken down while still in the enzyme’s active site, forming an enzyme-product complex.
4) The product molecule(s) leave the active site.
5) The enzyme is now available to form another ES complex.

Question 22

What is the induced-fit hypothesis?

Answer 22

Suggests that when the substrate binds to active site, it changes shape slightly to mould itself around the substrate molecule.

Question 23

What is activation energy?

Answer 23

The energy required to begin a chemical reaction.

Question 24

What is the importance of enzymes for activation energy?

Answer 24

In a living cell, the temperature cannot be raised too high or the proteins will be denatured.
Enzymes bring the substrate molecules close enough together to react, without the need of excessive heat.
They lower activation energy and speed up metabolic reactions.

Question 25

How does temperature effect enzyme activity?

Answer 25

As temperature increases, both substrate and enzyme gain kinetic energy which increases rate of successful collisions.
This increases the number of ES complexes formed.
At the optimum temperature, the reaction rate is at its maximum.

Question 26

What negative effects does temperature have on enzyme activity?

Answer 26

Increasing temperature makes the molecules vibrate.
This can break the weak hydrogen bonds holding the tertiary structure.
The active site changes shape and the substrate will no longer fit.
The enzyme is denatured.

Question 27

How do you calculate the rate of reaction?

Answer 27

1 ÷ time taken to reach end point

Question 28

What is temperature coefficient? (Q10)

Answer 28

The increase in the rate of a process when temperature increases my 10°C.

Question 29

How do you calculate temperature coefficient?

Answer 29

Rate of reaction at (T+10)°C ÷ Rate of reaction at T°C

Question 30

What is pH?

Answer 30

Indicates whether a substance is acidic, alkaline or neutral.

Question 31

What is a buffer?

Answer 31

Something that resists changes in pH. They can accept or donate hydrogen ions.

Question 32

What are hydrogen ions?

Answer 32

They are protons, if the hydrogen concentration is increased, then the substance becomes more acidic and the pH decreases.

Question 33

How does pH effect enzyme activity?

Answer 33

Hydrogen ions interfere with hydrogen bonds that hold the enzyme’s tertiary structure, changing the shape of the active site. They will also interfere with the charges of the active site.
This lowers the rate of reaction.

Question 34

What are the optimum pHs of certain enzymes in the body?

Answer 34

Intracellular enzymes= 7
Amylase in in the mouth= 8
Pepsin in the stomach= 1-2

Question 35

What does enzyme concentration in the body depend on?

Answer 35

The rate of enzyme synthesis and degradation.

Question 36

What is enzyme degradation?

Answer 36

When cells degrade old enzymes into their component amino acids and synthesise new ones.
This eliminates abnormally shaped proteins.

Question 37

What effect does enzyme concentration have on rate of reaction?

Answer 37

As enzyme concentration increases, more active sites on the enzyme become available.
More successful collisions occur.
More ES complexes are formed per unit of time.

Question 38

What happens if substrate concentration is fixed?

Answer 38

All the substrate molecules will be occupying an active site.
If the enzyme concentration increases further, there will be no increase in the reaction rate.

Question 39

How does substrate concentration effect enzyme activity?

Answer 39

As substrate concentration increases so does the rate of reaction.
This is because more ES complexes, and therefore products, can form.

Question 40

What happens if enzyme concentration is fixed?

Answer 40

Adding more substrate molecules will not increase the rate of reaction.
This is because all the enzyme’s active sites are occupied with substrate molecules.

Question 41

What are inhibitors?

Answer 41

Substrates that reduce the activity of an enzyme.

Question 42

What are competitive inhibitors?

Answer 42

When the inhibitor molecule has a similar shape to that of the substrate molecule and competes with the substrate for the enzyme’s active site.
They block the active site and prevent the formation of ES complexes.

Question 43

What are non-competitive inhibitors?

Answer 43

An inhibitor that attaches to an area of the enzyme other than the active site. They change the shape of the active site, preventing ES complexes from forming.
Some bind permanently while others bind temporarily.

Question 44

What is end-product inhibition?

Answer 44

Helps to regulate enzyme-catalysed reactions.

After the reaction has reached completion, product molecules stay tightly bound to the enzyme and cannot form products.