Enzymes

Question 1

Definition of enzyme

Answer 1

Biological catalysts that increase the rate of metabolic reactions in living organisms and remain unchanged at the end of the reaction.

Question 2

Problems with the ‘lock and key’ model

Answer 2

Does not explain allosteric effects, eg. Actions of inhibitors.

Question 3

‘Induced fit’ model stepwise

Answer 3

Substrate bunds disturbing the fine balance of flexible protein chain and altering the shape.
Substrate molecule distorted, straining bonds to lower activation energy.
Following catalysis, enzyme returns to original shape.

Question 4

Intracellular enzyme

Answer 4

Works and is synthesised within cells

Question 5

Examples of intracellular enzymes

Answer 5

Catalase, catalysing breakdown of H2O2 to water and oxygen

Question 6

Extra cellular enzymes

Answer 6

Synthesised in cells then secreted out of cells

Question 7

Extra cellular enzymes example

Answer 7

For extra cellular secretion for bacterial digestion.
In the human digestion system, eg, salivary amylase catalysing the hydrolysis of starch to maltose, and trypsin catalysing hydrolysis of peptide bonds.

Question 8

Methods of controlling enzymes within cells

Answer 8

Use an activator to make enzyme function, cofactors
Modify condition in the cell
Gene regulation, enzymes only produced as required
Inhibition

Question 9

Factors affecting enzyme activity

Answer 9

pH, enzyme concentration, temperature, substrate concentration.

Question 10

Effect of temperature on enzyme activity

Answer 10

Increasing temperature increases kinetic energy, hence particles move faster and collide more, higher chance of successful collision and higher rate.

Question 11

Optimum temperature and high temperature

Answer 11

Optimum is where the enzyme has the highest rate of activity.

At high temperatures, bonds holding proteins together vibrate and this causes them to have strain, at high temp bonds will break, changing the tertiary shape so the enzyme is denatured.

Question 12

Method of controlling temperature

Answer 12

Use of thermostatically controlled water baths.

Question 13

Optimum pH

Answer 13

pH at which the concentration of H+ ions in solution gives the most complementary tertiary structure, where active site is arranged in most complementary shape.

Question 14

Explanation of effect of pH on rate of reaction

Answer 14

Hydrogen and ionic bonds hold together tertiary structure .
Hydrogen ions interfere with bonds as positive charges attract negative and can ‘replace’ H bonds. Increasing concentration of H+ ions can alter charges around active site and so interfere with substrate binding.

Question 15

Enzyme concentration effect on rate of reaction

Answer 15

Increased concentration of enzyme means more active sites are available, and so faster rate of reaction.

Question 16

Substrate concentration effect on rate

Answer 16

Increased concentration increases rate as there are more collisions up to the point where all enzymes are active forming enzyme substrate complexes. And so graph flattens off.

Question 17

Method of controlling pH

Answer 17

Using a pH buffer

Question 18

Controlling enzyme and substrate concentration

Answer 18

Control by measuring volume, mass and surface area.

Question 19

Measuring enzyme action

Answer 19

Over course of reaction, product quantity increases and substrate increases, thus can measure substrate disappearance or product formation over time.

Question 20

Turnover number

Answer 20

Number of substrate molecules broken down by molecules of enzyme per unit of time.

Question 21

Initial rate of reaction

Answer 21

Shows trend better as rate decreases over course of reaction, close to when time = 0

Question 22

Cofactors

Answer 22

Non-protein substances which bind to enzymes enabling them to catalyse a reaction.

Question 23

Options for cofactors

Answer 23

Form part of the active site

Transfer atoms from one reaction to another in a multi-step pathway.

Question 24

Prosthetic groups

Answer 24

Are tightly bound to the enzyme and form a permanent feature of them.

Question 25

Ions and coenzymes

Answer 25

Can be loosely or temporarily bound.

Inorganic ions are often obtained via the diet as minerals, and coenzymes often come from vitamins.

Question 26

Example of an organic prosthetic group

Answer 26

Catalase, containing 4 prosthetic haem groups (catalysers breakdown of H2O2)

Question 27

Example of an inorganic prosthetic group

Answer 27

Zn2+ ions form a permanent part of the structure of carbonic anhydrase.

Question 28

Example of a coenzyme

Answer 28

Alcohol dehydrate needs NAD (synthesised using vitamin B3) to accept the hydrogen produced when ethanal is formed from ethanol.

Question 29

Example of an inorganic ion cofactor

Answer 29

Chloride ions, needed for the formation of the amylase active site.

Question 30

Enzyme inhibitor

Answer 30

Factor that prevent or reduces the fate of an enzyme-catalysed reaction.

Question 31

End product inhibition

Answer 31

When the product of a reaction acts as an inhibitor to the enzyme that produces it.
Eg. Respiration
Serves as a negative feedback control mechanism.

Question 32

Competitive inhibition

Answer 32

Inhibitor occupies active site preventing substrate access and so decreasing number or enzyme-substrate complexes that can form.

Question 33

Non-competitive inhibition

Answer 33

Inhibitor binds at site other than he active site (allosteric) causing rhe tertiary structure of the enzyme to change, and thus the active site so that the substrate cannot bind.

Question 34

Differences between competitive and non-competitive inhibition.

Answer 34

Competitive: similar shape to substrate molecule
Competes for active site so is overcome by suitably high substrate concentration
Non-competitive: reduces max rate of reaction irrespective of substrate concentration as enzymes are rendered ununseable

Question 35

Examples of competitive inhibitors

Answer 35

Ethylene glycol in antifreeze is poisonous when consumed, treatment is severe intoxication as alcohol inhibits rate of oxalic acid production.

Protease inhibition used in the treatment of HIV, inhibiting production of new viral protein coats.

Question 36

Examples of non-competitive inhibitors

Answer 36

Penicillin inhibits enzyme involved in synthesis of bacteria cell walls causing them to burst.

Cyanide binds to an enzyme in respiration inhibiting production of ATP

Question 37

Reversible inhibitors

Answer 37

Binding with hydrogen bonds can be overcome, tis including most competitive inhibitors

Question 38

Non-reversible inhibitors

Answer 38

Cannot be removed from the part of the enzyme they are attached too. Denature enzyme if covalent bonds are formed and so generally highly toxic.

Question 39

Q10

Answer 39

The temperature coefficient

Measurement of the effect of a 10 degree rise on the rate of enzyme controlled activity.

Question 40

Formula for Q

Answer 40

rate of reaction at t + 10 degrees C /

Rate of reaction at t degrees C