1.4 Enzymes

Question 1

Define metabolism

Answer 1

• all the organisms chemical processes, comprising anabolic and catabolic pathways

Question 2

What is a metabolic pathway

Answer 2

A sequence of enzyme controlled reactions in which a product of one reaction is a reactant in the next

Question 3

Define an enzyme

Answer 3

• biological catalyst
• globular protein made by cells that alters the rate of a chemical reaction without being used up itself

Question 4

What structure are enzymes in?

Answer 4

Tertiary (globular)

Question 5

Are enzymes soluble or insoluble?

Answer 5

• soluble as R groups of enzymes are hydrophilic
• active site is insoluble due to hydrophobic R groups

Question 6

Extracellular enzymes

Answer 6

• secreted (exocytosis) from cell for outside action
• eg amylase made in salivary glands moves down duct ti the mouth

Question 7

Intracellular (solution) enzymes

Answer 7

• act inside solution in cells ie cytoplasm
• eg enzymes that catalyse glycolysis (respiration stage in cytoplasm) or enzymes in stroma of plants that catalyse photosynthesis

Question 8

Intracellular (membrane bound) enzymes

Answer 8

• attached to membranes
• eg cristae of mitochondria for ATP formation

Question 9

What is the enzyme for hydrogen peroxide break down?

Answer 9

• catalase
• hydrogen peroxide damages dna in cell if not broken down

Question 10

Explain the lock and key model

Answer 10

• enzyme and the active site are perfectly complimentary so each enzyme only catalyses one type of reaction
• active site does not change
• able to synthesise and split molecules
• temporary bonds form enzyme substrate complex

Question 11

Explain the induced fit model

Answer 11

• active site flexible - alters slightly to accommodate substrate
• ie lysozyme in mucus and tears - groove molds to substrate

Question 12

Define activation energy

Answer 12

• minimum energy that must be put into a chemical system for a reaction to occur

Question 13

How do enzymes speed up chemical reactions?

Answer 13

• lower activation energy
• reactions can take place at lower temp
• modify substrate

Question 14

How does temperature influence rate of reaction?

Answer 14

• increases as temp increases as more KE so greater rate of successful collision (therefore more enzyme-substrate complexes)
• rate falls after optimism as the enzyme/active site denatures
• optimum temp in mammals is 37.5

Question 15

How does pH influence rate of reaction?

Answer 15

• anywhere away from optimum pH decreases the rate
• alters some of the charges in the active site which disrupts H bonds in tertiary structure - reversible but can become permanent
• extreme changes result in key bonds in tertiary breaking, altering the AS shape and therefore denatured enzyme

Question 16

How does enzyme/substrate concentration influence rate of reaction?

Answer 16

• increase and then plateau once become saturated and no more substrates or enzymes left
• prevent plateau by adding more substrates/enzymes

Question 17

Define turn over rate

Answer 17

• the number of substrate molecules an enzyme can catalyse in a given time

Question 18

Define an inhibitor

Answer 18

A molecule/ion that binds to an enzyme and reduces the rate of reaction that an enzyme catalyses

Question 19

Define competitive inhibition

Answer 19

Reduction of the rate of reaction of an enzyme controlled reaction by a molecule/ion that is complementary to the active site of an enzyme and so binds to it, preventing the substrate from binding

Question 20

Define non-competitive inhibition

Answer 20

A molecule/ion that reduces the rate of reaction by binding to an enzyme at an allosteric site, altering its tertiary structure and therefore the shape of its active site, meaning that substrates can no longer bind

Question 21

Define Vmax

Answer 21

Maximum rate of reaction of an enzyme controlled reaction when the reaction is concentrated with substrates

Question 22

What are immobilised enzymes?

Answer 22

• enzyme molecules that bind to an inert material over which the substrate molecules move
• used in industrial processes like fermentation or making lactose free milk
• immobilising enzymes makes them more stable

Question 23

Advantages of immobilised enzymes

Answer 23

• increased stability and function at range of pH and temp
• products are not contaminated
• enzymes easily recovered for reuse
• enzymes easily added or removed -> controlled reaction
• sequence of columns with different enzymes can be used

Question 24

What is the difference between bacterial amylase and human amylase?

Answer 24

• diff optimum temps
• human is 37 whereas bacterial shows 100

Question 25

Anabolic reactions

Answer 25

Synthesise molecules

Question 26

Catabolic reactions

Answer 26

Break down molecules

Question 27

Uses of immobilised enzymes in food industry

Answer 27

- pectinases break down pectin so a good quality fruit juice is obtained - lactase breaks down lactose in milk to galactose and glucose so can be digested by lactose intolerant people

Question 28

What are the 3 methods of immobilising enzymes?

Answer 28

1. Entrapment - enzymes in a membrane bound structure ie alginate beads 2. Carrier bound - bound to membrane by either adsorption or covalent bonds 3. Cross linking

Question 29

Why is there a tap on an immobilised enzyme column?

Answer 29

To regulate the flow rate ensuring that lactose is broken down

Question 30

What are some properties of biosensors?

Answer 30

Rapid, sensitive and specific measurement of products —> high turnover rate and specific to substrates

Question 31

How does a blood glucose biosensor work?

Answer 31

- electrical probe w a specific immobilised enzyme in the membrane is placed in blood sample - if glucose present it diffuses through membrane and forms enzyme substrate complex - reaction produces a small electrical current which is detected by electrode and read by a meter which then displays the glucose reading

Question 32

What causes the active sites of enzymes to do denature?

Answer 32

- temp: vibrations cause H bonds to break which alters the tertiary structure, leading to changed shape of active site —> above optimum

Question 33

Why do enzymes only catalyse 1 reaction?

Answer 33

- enzymes have specific active site for a substrate - substrate and active site complimentary - binds to form enzyme substrate complex

Question 34

More … collisions lead to …

Answer 34

- successful - more enzyme substrate complexes formed therefore more product

Question 35

How do you reduce the effect of an inhibitor?

Answer 35

Increase the concentration of the substrate

Question 36

Why would it be inappropriate to use a buffer in an experiment with a colorimeter?

Answer 36

- colour change is dependant on pH - hydrolysis produces fatty acids which lower pH - buffer would stabilise/control the pH

Question 37

How can a diet high in cholesterol lead to a person developing heart disease?

Answer 37

- increase levels of LDL - increase incidence of atheromas in the arteries

Question 38

What is a biosensor?

Answer 38

A device that uses biological molecules (ie immobilised enzymes) to detect the presence of chemicals/molecules in a solutiom