2:1:4 Enzymes

Question 1

What are enzymes

Answer 1

Biological catalysts (speed up the rate of chemical reactions without being used up)

Question 2

What is the structure of enzymes

Answer 2

Globular proteins with complex tertiary structures, or sometimes quaternary structures, produced via protein synthesis

Question 3

Why are enzymes important

Answer 3

Control metabolic pathways, where almost every metabolic reaction is catalysed by an enzyme, so they are essential for life

Question 4

What is an intracellular enzyme

Answer 4

An enzyme that is produced and function (is active) inside the cell

Question 5

What is an extracellular enzyme

Answer 5

An enzyme that is secreted by cells and function (is active) outside the cell

Question 6

What is an example of an intracellular enzyme and its function

Answer 6

• Catalase
• Hydrogen peroxide produced as a byproduct of metabolic reactions and is harmful to cells
• Catalase converts hydrogen peroxide into water and oxygen to prevent harm to cells

Question 7

What is an example of an extracellular enzyme

Answer 7

• Amylase
• Secreted by the salivary glands and pancreas
• Digestion carried out by extracellular enzymes as macromolecules digested need to be broken down to enter the cell
• Amylase hydrolyses starch into maltose

Question 8

What is trypsin

Answer 8

An extracellular digestive enzyme that is secreted by the pancreas, which breaks proteins into peptides and amino acids

Question 9

How do fungi feed

Answer 9

Through extracellular digestion, where hyphae of fungi secrete enzymes directly onto their food so that it can be broken down and be absorbed through the hyphae walls

Question 10

What is an active site

Answer 10

The specifically shaped site on an enzyme where specific substrates bind forming an enzyme-substrate complex

Question 11

What is denaturation

Answer 11

When extreme heat or pH changes the shape of the active site, which prevents the substrate from binding and denatures the enzyme

Question 12

What is the enzyme substrate complex and how is it formed

Answer 12

• Formed when the substrate collides with the enzyme at the correct orientation and speed
• Formed temporarily before enzyme catalyses the reaction and products are released

Question 13

What is enzyme specificity

Answer 13

The complementary nature between the shape of the active site (determined by the complex tertiary structure of the protein) and its substrate

Question 14

What is the lock and key hypothesis

Answer 14

Emil Fischer’s (1890’s) first model of enzyme activity suggested that both enzymes and substrates were rigid structures that locked into each other precisely

Question 15

What is the induced fit hypothesis

Answer 15

The modified understanding of lock and key enzyme activity, where the enzyme and substrate interact so the enzymes active site can change shape slightly as the substrate enters the enzyme (conformational change) which ensures ideal binding arrangement, maximising the ability of the enzyme to catalyse the reaction

Question 16

What is activation energy

Answer 16

The amount of energy needed by the substrate to become just unstable enough for a reaction to occur and its products to be formed

Question 17

How do enzymes speed up chemical reactions

Answer 17

Reducing the stability of bonds in the reactants (substrate) making it more reactive

Question 18

How do enzymes speed up a reaction

Answer 18

They provide an alternative energy pathway with a lower activation energy, so that high temperatures and pressures (which would kill cells) aren’t needed for the reactants to gain the required energy

Question 19

How is enzyme activity affected by pH

Answer 19

• Enzymes have an optimum pH
• In extreme pH’s (excess H+ or OH-) the hydrogen and ionic bonds in the tertiary structure of the protein are broken
• The active site shape is changed causing the enzyme substrate complex to stop forming
• The enzyme denatures

Question 20

Describe the process to test the effect of pH on enzymes

Answer 20

• Place single drops of iodine solution on a spotting tile
• Add 2cm^3 of amylase (enzyme) to a test tube with the pH to be tested
• Add 1cm^3 buffer solution to the test tube
• Add 2cm^3 of starch solution to the test tube and start a stopwatch and mix
• In 10 second increments add a drop of the solution to the iodine spots
• Iodine solution is orange/brown, but turns blue/black in starch, which is broken down by amylase, so when the iodine solution remains orange/brown, all the starch has been broken down
• Serial dilution and colorimeter can be used to test amount of amylase present

Question 21

How is enzyme activity effected by low temperature

Answer 21

• Enzymes have specific optimum temperatures
• Low temperatures slow down reactions as molecules move slowly due to less kinetic energy
• There are less frequent and successful collisions between the substrate and enzyme, so less substrate enzyme complexes form
• Also substrates and enzymes collide with less energy, so it’s less likely for bonds in the substrate to be broke/formed

Question 22

How is enzyme activity effected by high temperatures

Answer 22

• Enzymes have optimum temperatures
• High temperatures cause enzymes to speed up as molecules move more quickly due to more kinetic energy
• There are a higher frequency of successful collisions between the substrate and enzyme so the enzyme substrate complex forms more
• Also substrates and enzymes collide with more energy, so it’s more likely for bonds in the substrate to be formed/broken

Question 23

How does temperature denature enzymes

Answer 23

• If temperatures increase past a certain point, enzyme molecules have too much kinetic energy and vibration, putting a strain on them causing the hydrogen and ionic bonds to break
• This causes the tertiary structure to change
• The active site becomes permanently damaged and is no longer complementary to the substrate so the enzyme substrate complex can’t form
• The enzyme denatures

Question 24

What are anabolic reactions

Answer 24

Chemical reactions required for growth, catalysed by enzymes

Question 25

What are catabolic reactions

Answer 25

Chemical reactions that break down molecules to release energy, catalysed by enzymes

Question 26

Graph to show the effect of pH on enzyme activity

Answer 26

Question 27

Graph to show the effect of temperature on enzyme activity

Answer 27

Question 28

How is the optimum/denaturation temperature of an enzyme decided

Answer 28

- Varies due to the habitat in which an organism has adapted - Most enzymes in organisms denature at 60 degrees - Few human enzymes function above 50 degrees - Thermostable enzymes can withstand high temperatures

Question 29

What is the temperature coefficient

Answer 29

The ratio between the rates of a biological reaction at two different temperatures: Q= (rate of reaction of x) / (rate of reaction of x + 10 degrees) Q10=2

Question 30

How does enzyme concentration affect enzyme activity

Answer 30

- The higher the concentration, the greater the number of active sites, the more likely for enzyme substrate complex to form - With sufficient substrate availability the rate of reaction increases linearly - Rate of reaction will plateau eventually due to lack of substrate (limiting factor)

Question 31

How does substrate concentration effect enzyme activity

Answer 31

- The higher the substrate concentration, the higher the rate of reaction - More substrates mean it’s more likely for enzyme substrate complexes to form, and if there is a sufficient amount of enzymes, the rate of reaction with increases linearly - The rate of reaction eventually plateaued as the active sites become saturated and the substrates have nowhere to bind and form the enzyme substrate complex

Question 32

What are reversible inhibitors

Answer 32

Inhibitors that can temporarily reduce or stop an enzymes activity

Question 33

What are competitive inhibitors

Answer 33

Inhibitors with similar shapes to the substrate molecules, so compete with the substrate for the active site

Question 34

What are non-competitive inhibitors

Answer 34

Inhibitors that bind to the enzyme at an alternative site, which alters the shape of the active site and prevents the substrate from binding to it

Question 35

How to increase the rate of reaction with inhibitors

Answer 35

- Increasing the substrate concentration can increase the rate of reaction with competitive inhibitors by countering the increase in inhibitor concentration - As non-competitive inhibitors change the active site, increasing the substrate concentration doesn’t increase the rate of reaction

Question 36

What are irreversible inhibitors

Answer 36

Inhibitors that form covalent bonds with enzymes and inhibit them permanently, resulting in the complete inactivation of the enzyme (metabolic poisons)

Question 37

Why are some irreversible inhibitors dangerous and how can they be avoided

Answer 37

- They can cause the biological reaction the enzyme is catalysing to completely stop - E.g. Cyanide stops a metabolic reaction by acting as an irreversible inhibitor to cytochrome oxidase, an enzyme that is key in reactions of aerobic respiration - Can be avoided by the organism producing more of the enzyme being inhibited by protein synthesis

Question 38

What is an example of a beneficial irreversible inhibitor

Answer 38

Penicillin is an irreversible inhibitor of the enzymes that form the cross links in bacterial cell walls, but has a medical benefit as it results in the destruction of bacteria by breaking down the cell walls

Question 39

What is end product inhibition

Answer 39

- Where an enzyme converts the substrate into a product, which then binds to an alternative site on the enzyme, changing its active site and preventing the enzyme substrate complex from forming - The end product can detach and be used elsewhere, allowing the active site to reform and the enzyme to become active - As product levels fall, the enzyme can catalyse again so its a continuous feedback loop

Question 40

How do reversible inhibitors act as regulators in metabolic pathways

Answer 40

Metabolic reactions are tightly controlled and balanced, and the end product of a sequence of metabolic reactions can be used as a non-competitive reversible inhibitor to control the metabolic reactions

Question 41

What are cofactors

Answer 41

Inorganic ions that help to stabilise the structure of the enzyme, or take part in the reaction at the active site to help the enzyme to function (e.g. chloride ions are cofactors for amylase)

Question 42

What are coenzymes

Answer 42

Large non-protein organic cofactors sourced from vitamins which can be permanently bonded or temporarily bonded in or near the active site, which are involved in carrying electrons or chemical groups between enzymes to help them function

Question 43

How do coenzymes work

Answer 43

- Link enzyme catalysed reactions into a sequence during metabolic processes - E.g. ATP is responsible for the transfer of phosphate groups between respiration and energy consuming processes in cells - Coenzyme A is responsible for the transfer of acetyl groups from fatty acids and glucose in respiration

Question 44

What are prosthetic groups

Answer 44

Cofactors which are permanent parts of the enzyme structure, which help the function of the enzyme by forming its final 3D

Question 45

Describe a practical to measure catalase activity

Answer 45

- Potato cubes (source of catalase) are placed in a conical flask with hydrogen peroxide - A bung with a delivery tube that links to a water bath and gas collecting tube is placed on the conical flask - The catalase breaks down the hydrogen peroxide into oxygen and water, and the volume of oxygen generated is measured in a set time - Rate of reaction is calculated