Enzymes

Question 1

Significance of Vmax

Answer 1

Maximum rate of reaction, different for different enzymes and reflects their turnover number

Question 2

Km

Answer 2

Gives you an idea of the efficiency of enzymes - higher turnover, higher Km

Half Vmax

Question 3

Without enzymes

Answer 3

Most of body’s biochemical reactions would be too slow

Enzymes are proteins, identified using Biuret test (purple)

Question 4

Enzymes

Answer 4

Speed up reactions without being changed at the end of the reaction

Only speed up 1 reaction as they are specific

Can be intracellular (DNA helical and DNA polymerase)

Or extracellular (digestive enzymes eg amylase that catalyse hydrolysis reactions)

Question 5

Intracellular

Answer 5

Synthesised in the cell and work in the cell

Question 6

Extracellular

Answer 6

Synthesised in the cell and works outside the cell

Question 7

Zymase

Answer 7

First enzyme to be discovered, in yeast

Catalyses conversion of sugars to alcohol

Question 8

Properties of enzymes

Answer 8

• generally work very rapidly
• not destroyed or used up by the reactions that they catalyse
• they are specific, work by the lock and key hypothesis so they are only found in small amounts inside cells
• proteins, and are chains of amino acids
• complex tertiary structure held together by hydrogen, ionic and disulphide bonds
• denatured by several factors including high temperatures and pH changes

Question 9

Practical application

Answer 9

Catalase is an enzyme found in all living cells, and it speeds up the breakdown of hydrogen peroxide inside the cells to the products water and oxygen

Good sources of catalyse include liver, potato and celery

2H2O2 > 2H2O + O2

V fast turnover rate

Question 10

Turnover rate

Answer 10

No substrate molecules converted into products

Question 11

Reactions at low temperatures

Answer 11

Enzymes ensure reactions can happen at relatively low temperatures

They lower the activation energy of the reaction

Activation energy is the minimum energy required to overcome the repulsion between molecules

They do this by forming an E-S complexes and bending bonds

Question 12

Formation of an enzyme-substrate complex increases the rate of reaction

Explain how

Answer 12

By lowering activation energy by bending bonds

Question 13

Explain why maltase only breaks down maltose

Answer 13

Tertiary structure means the active site is complementary to maltose

Description of induced fit

Enzymes lower activation energy by forming E-S complexes

Question 14

Once reaction is complete

Answer 14

The enzyme is free to bind with another molecule of substrate

Question 15

Enzymes type

Answer 15

Globular protein with a complex tertiary structure

The combination of the enzyme with its substrate molecules is called an E-S complex and the part of the enzyme that fits with the substrate is called the active site

Question 16

Prosthetic groups

Answer 16

Some have prosthetic groups that are non-protein and some are activated by inorganic ions e.g. ATP hydrolyse and calcium ions

Question 17

Globular

Answer 17

As globular proteins, anything that affects the 3D shape, affects the ability of the enzyme to do its job

Question 18

Lock and key hypothesis

Answer 18

Enzymes are specific to the reactions that they catalyse

Only 1 substrate or type of substrate will fit into the active site

The active site and substrate are complementary shapes

The ability of the enzyme to combine with the substrate is due to its tertiary shape

Question 19

Induced fit hypothesis

Answer 19

Enzymes and substrate slot together to form a E-S complex which enables the enzyme to lower the activation energy

Once the reaction has been catalysed, the products are no longer complementary shapes to the active site and the complex breaks up

Releasing the products and freeing the enzyme for further catalytic action

Question 20

Induced fit development

Answer 20

Built on the lock and key hypothesis, suggesting that enzymes are more flexible and can mould to the shape of the substrate when it enters the active site