enzymes

Question 1

what are metabolic reactions

Answer 1

Metabolic reactions encompass both anabolic and catabolic reactions, which are two distinct types of biochemical processes within metabolism:

Question 2

what are anabolic reactions

Answer 2

Reactions in which large molecules are built up from smaller molecules are called anabolic reactions.

Question 3

what are catabolic reactions

Answer 3

Reactions that *split large molecules** into smaller ones are called catabolic reactions.

Question 3

enzyme definition

Answer 3

Enzymes can be defined as biological catalysts. Most enzymes are proteins.

Question 4

what is a catalyst

Answer 4

A catalyst is a substance which speeds up a chemical reaction but remains unchanged itself at the end of the reaction.

Question 5

what do enzymes do

Answer 5

Thus, enzymes increase the rates of chemical reactions without themselves being chemically changed at the end of the reaction.

Question 6

so how do enzymes increase rates of chemical reactions

Answer 6

They speed up a chemical reaction by lowering the activation energy barrier required to start a reaction.

Question 7

Anabolic reactions on amino acids in a cell

Answer 7

**Amino acids* taken into the cells may be used to build up proteins.

Question 8

anabolic reactions on glucose molecules in a plant cell

Answer 8

In plant cells, glucose molecules are joined together to form cellulose to be added to the cell wall.

Question 9

Catabolic reactions in digestion

Answer 9

Inside the alimentary canal, large, water-insoluble molecules are hydrolysed (broken down) to smaller ones in the process of digestion.

Question 10

how does starch digest
enzyme + product

Answer 10

Starch is digested to sugar by an enzyme called amylase.

Question 11

how does protein digest
enzyme + product

Answer 11

Protein is digested to amino acids by protease.

Question 11

how does fats digest
enzyme + product

Answer 11

Fats are digested to fatty acids and glycerol by lipase.

Question 12

what can pass through the wall of the small intestine and into the blood without an enzyme

Answer 12

The simpler, smaller substances are soluble in water and they can pass through the wall of the small intestine and into the blood.

Question 12

during cellulose respiration what happens to glucose

Answer 12

Glucose is oxidised to release energy in the form of ATP molecules, forming carbon dioxide and water.

Question 13

what is hydrogen peroxide

Answer 13

Sometimes during chemical reactions in the cells, hydrogen peroxide, a toxic substance, is produced

Question 14

how does the body deal with hydrogen peroxide since its toxic

Answer 14

The cells produce an enzyme called catalase which catalyses the breakdown of hydrogen peroxide to water and oxygen. This enzyme is abundant in liver cells and potato cells.

Question 14

can enzymes act on other substrates

Answer 14

Enzymes are highly specific in their action, e.g. amylase will only act on starch, and not on proteins or fats.

Question 15

what are substrates

Answer 15

The substances on which the enzymes act are called substrates, e.g. starch, proteins, fats.

Question 16

what is the active site

Answer 16

Only a restricted region of the enzyme molecule actually binds to the substrate. This region is called the active site. The active site is usually formed by only a few of the enzyme’s amino acids.

Question 17

what is the lock and key hypothesis

Answer 17

The ‘lock and key’ hypothesis states that there is an exact fit between substrate (‘key’) and enzyme active site (‘lock’).

Question 18

y is an enzyme so specific

Answer 18

The specificity of an enzyme is due to its very precise three-dimensional conformation that allows a complementary fit between the substrate and the active site.

Question 19

what is the induced fit hypothesis

Answer 19

According to the ‘induced fit’ hypothesis, when a substrate molecule fits into an enzyme molecule, the active site alters its shape slightly so that it fits more tightly around the substrate molecule to facilitate the chemical reaction.

Question 20

how are enzyme-substrate complexes formed

Answer 20

Binding of substrate molecule(s) at the active site of the enzyme molecule as the three- dimensional conformation of the enzyme active site is complementary to that of the substrate(s)

Question 21

after binding into ES complexes

Answer 21

(iii) Chemical reactions that convert the substrate molecule(s) into product molecule(s)
(iv) Separation of product molecule(s) from the active site
(v) Free, unchanged enzyme molecule combines with more substrate molecules

Question 22

CHARACTERISTICS OF ENZYMES

Answer 22

1. Most enzymes are proteins in nature.
2. Enzymes are unchanged at the end of the chemical reaction.
3. Enzymes can be used over and over again, thus they are required in small amounts.
4. Enzymes are specific in their action.
5. Enzymes are sensitive to changes in temperature and pH. Each enzyme has an optimum
   temperature and pH at which they work most efficiently.
6. Enzymes may require cofactors to be bound to them before they can catalyse reactions.
7. The action of enzyme can be inhibited by chemical inhibitors that bind to them.
8. Most enzymes can catalyse reversible reactions. A + B <-> C + D
9. An extracellular enzyme is an enzyme that is secreted by a cell and functions outside the cell. An intracellular enzyme is an enzyme that functions within the cell in which it was produced.

Question 23

how can the rate of reaction be measured

Answer 23

(i) the amount of product(s) formed per unit time; or
(ii) the amount of substrate(s) that disappeared per unit time.

Question 24

what happens to enzymes at low temperatures

Answer 24

they inactivate

Question 25

what happens to enzymes when the temperature increases

Answer 25

As the temperature increases, its activity increases. The rate of reaction also increases. This is because there is an increase in kinetic energy of enzyme and substrate molecules. As they move about more rapidly, the frequency of effective collisions between substrate molecules and the enzyme’s active site increases. The rate of enzyme-substrate complex formation increases.

Question 26

how much more active does the enzyme get as the temperature increases

Answer 26

The enzyme is about twice as active for every 10C rise in temperature until the optimum temperature is reached.

Question 27

What is the optimum temperature mean for enzymes and most common temp

Answer 27

The optimum temperature is the temperature at which the rate of reaction occurs fastest or at which enzyme activity is the greatest. For most enzymes, this is about 40 - 45C.

Question 28

what happens to enzymes at high temperatures

Answer 28

High temperature (thermal agitation) disrupts the non-covalent bonds that stabilise the three-dimensional conformation of the enzyme molecule. The specific three-dimensional conformation of the enzyme active site is altered and the active site is no longer complementary to the shape of substrate. No enzyme-substrate complex is formed. This is called enzyme denaturation.

Question 29

how does small changes in pH affect enzymes

Answer 29

Although small changes in pH affect the activity of enzymes, these effects are usually reversible, that is, an enzyme which is inactivated by a low pH will resume its normal activity when its optimum pH is restored.

Question 30

how does extreme changes in pH affect enzymes

Answer 30

Extreme changes in pH may denature some enzymes irreversibly by changing the three-dimensional conformation of the enzyme molecule and altering the shape of the active site.

Question 31

what is a limiting factor

Answer 31

A limiting factor is any factor that is in the shortest supply so it directly affects the rate of reaction. The value of this factor has to be increased in order to increase the rate of reaction.

Question 31

As enzyme concentration increases, the rate of reaction increases up to a point when any further addition of enzyme has no effect on the rate. This is represented by the plateau part of the graph, corresponding to the maximum rate of reaction. y is this so

Answer 31

There are not enough substrate molecules to occupy all the enzyme active sites at any given moment. At high enzyme concentration, substrate concentration becomes limiting.

Question 32

state and explain which is the limiting factor at low enzyme concentration

Answer 32

enzyme concentration is limiting. insufficient enzyme active sites to bind with all the substrate molecules at any given moment.

Question 33

state and explain which is the limiting factor at high enzyme concentration

Answer 33

substrate concentration is limiting. Insufficient substrate molecules to occupy all the available enzyme active sites at any given moment.

Question 34

state and explain which is the limiting factor at low substrate concentration

Answer 34

substrate concentration is limiting. insufficient substrate molecules to bind with all the enzyme active sites at any given moment.

Question 35

state and explain which is the limiting factor at high substrate concentration

Answer 35

enzyme concentration is limiting. insufficient enzyme active sites to bind with all the substrate molecules at any given moment.

Question 36

what are irreversible inhibitors

Answer 36

irreversible inhibitors bind tightly and permanantly to enzymes and destroy their catalytic properties. these effects occur at very low concentrations of inhibitor.

Question 37

what are reversible inhibitors

Answer 37

reversible inhibitors bind less tightly to an enzyme. they can be classified as competitive or non competitve inhibitors.

Question 38

Techniques for immobilisation:

Answer 38

1 Chemical (covalent) attachment of enzyme to a solid support (cellulose fibres).
2 Entrapment of enzyme in beads of jelly-like substance sodium alginate. The pores are large enough to let the substrate in, but not the enzyme out.
3 Adsorption of enzyme to various surfaces but attachment is not permanent.

Question 39

advantages pf immobilised enzymes

Answer 39

1 The enzymes are easy to recover, so that they can be used over and over again.
2 Prevents losses due to flushing away of enzymes.
3 The product does not contain enzymes, so it does not need expensive purification.
4 The immobilisation of the enzyme often makes them more resistant to temperature and pH changes.

Question 40

Disadvantages of using immobilised enzymes:

Answer 40

1 Losses of enzyme activity can occur during the preparation of beads.
2 Diffusion of substrates and products may be hampered, so rate of catalysis may be lowered.
3 The enzyme may have a more constrained conformation in the immobilised state, giving it a lower catalytic activity.
4 There may be a high initial investment for immobilisation, compared to free enzyme.