1.4 - Biological reactions are regulated by enzymes

Question 1

What is metabolism?

Answer 1

a series of enzyme-controlled reactions in the body

Question 2

What are the two main types of reaction?

Answer 2

Anabolic reaction
Catabolic reaction

Question 3

What does an anabolic reaction do? What does a catabolic reaction do?

Answer 3

Anabolic: protein synthesis where amino acids are built up into more complex polypeptides
Catabolic: digestion of proteins, where complex polypeptides are broken down into simple amino acids

Question 4

what are enzymes?

Answer 4

all enzymes are tertiary globular proteins where the protein chain is folded back on itself into a spherical or globular shape

Question 5

what can enzymes be described by and what does this mean?

Answer 5

can be described as biological catalysts as they speed up the rate of metabolic reaction, but they are not changed by the reaction and do not get used up.

Question 6

where are all enzymes made?

Answer 6

inside the cell

Question 7

what are the sites of enzyme action?

Answer 7

extracellular
intracellular

Question 8

What are the two different models for enzyme reaction?

Answer 8

1. lock and key theory
2. induced fit hypothesis

Question 9

What does the lock and key model suggest?

Answer 9

that the substrate has a complementary shape to the enzymes active site and therefore that many enzymes only catalyse one substrate

Question 10

What does the induced fit hypothesis suggest?

Answer 10

active site of enzyme changes shape slightly to accommodate the substrate to form an enzyme substrate complex, the reverts to it’s original active site shape

Question 11

what is the example for the induced fit hypothesis? And how does it work?

Answer 11

the enzyme lysozyme
it is an antibacterial enzyme in human saliva, tears and mucus
it attaches to the wall of bacteria and breaks glycosidic bonds

Question 12

what does itt mean if an enzyme has disulphide bonds present?

Answer 12

it is likely to withstand quite high temperatures

Question 13

Enzymes are biological catalysts. How do they bring about the effect of speeding up a reaction?

Answer 13

The substrates fit into the active site of the enzyme and therefore lowers the activation energy

Question 14

What are the four factors affecting enzyme rate of reaction?

Answer 14

1. substrate concentration
2. temperature
3. pH
4. enzyme concentration

Question 15

how does substrate concentration effect the enzyme rate of reaction?

Answer 15

when the substrate increases in an enzyme-controlled reaction, there is a greater chance of a successful collision between the substrate and the enzyme, resulting in more enzyme-substrate complexes forming.

Question 16

what is a plateau?

Answer 16

the maximum rate of reaction for the conditions reached

Question 17

how does temperature effect the enzyme rate of reaction?

Answer 17

temp increases, enzyme and substrate molecules gain mroe kinetic energy, increasing chance of more successful collisions, therefore increasing chance of more substrate complexes formed.

Question 18

what happens above the optimum rate of reaction for enzymes?

Answer 18

rate of reaction decreases rapidly as hydrogen bonds in the tertiary structure break due to increased vibrations resulting in a change to the shape of the active site (denaturing)

Question 19

how does pH effect the enzyme rate of reaction?

Answer 19

• a change in H+ or OH- can affect the bonds of the enzymes tertiary structure, causing a change in the active site
• the active site is no longer complimentary to the substrate so fewer enzyme substrate complexes are formed which is irreversible

Question 20

What does OH- do to the pH? H+?

Answer 20

OH- increases pH
H+ decreases pH

Question 21

What does a competitive inhibitor do?

Answer 21

interferes with the active site of the enzyme so the substrate cannot bind

Question 22

How does a competitive inhibitor work?

Answer 22

It has a similar shape to the substrate and it is complimentary to the active site of the enzyme, this means it can block up the active site which forms an enzyme-inhibitor complex.
Therefore, this limits the number of enzyme substrate complexes that can form. Enzyme does not catalyse the reaction so no products formed, which reduces the reaction rate

Question 23

how does a non-competitive inhibitor work?

Answer 23

Attaches to an enzyme on the allosteric site, in doing so it changes the shape of the active site which means that enzyme-substrate complexes cannot form and thus no catalysis can happen(no product formed)

Question 24

What would a graph with a competitive inhibitor look like compared to without an inhibitor?

Answer 24

lower rate of reaction, eventually producing the same amount as without the inhibitor but it takes longer

Question 25

What would a graph with a non-competitive inhibitor look like compared to without an inhibitor?

Answer 25

lower rate of reaction never producing the same amount as no product formed

Question 26

What are immobilised enzymes?

Answer 26

enzymes that are fixed to an inert matrix

Question 27

What are the two ways in which immobilised enzymes can be achieved?

Answer 27

1. entrapment - held inside a gel eg silica gel
2. micro-encapsulation - trapped inside a micro-capsule eg alginate beads

Question 28

What are the advantages to immobilised enzymes?

Answer 28

1. enzyme can be easily recovered and reused
2. product is not contaminated by the enzyme
3. more stable at higher temp
4. catalyse reactions in a wider range of pH

Question 29

What is the result in immobilising enzymes?

Answer 29

several enzymes with different temperature and pH optima can be used at the same time and enzymes can be easily added or removed giving greater control over the reaction.

Question 30

What is an example of micro-encapsulation and how does it work?

Answer 30

Alginate beads
- beads containing the enzyme can be packed into glass column, and substrate added at one end
- rate of flow of substrate over beads can be controlled with a slower flow rate giving more time for enzyme-substrate complexes to form therefore yield more product
- bc enzymes in own ‘micro-environement’ enzymes are less susceptible to changes in pH, temp and action of chemicals such as organic solvents

Question 31

What is a buffer solution and what does it do?

Answer 31

a chemical that resists changes in pH
it neutralises excess acids or alkali’s and can be used to maintain the pH for a reaction