Module 2.1.4 - Enzymes

Question 1

What are enzymes?

Answer 1

Proteins that speed up the rate of a chemical reaction by acting as a biological catalyst

Question 2

What do enzymes do?

Answer 2

• Catalyze metabolic reactions at a cellular level and for an organism as a whole
• can affect structures in an organism (involved in production of collagen)
• enzyme action can be intracellular or extracellular

Question 3

What is an intracellular example?

Answer 3

Catalyze an enzyme that works inside cells to catalyze the breakdown of hydrogen peroxide to oxygen and water. Hydrogen peroxide is the toxic by-product of several cellular reactions (can kill cells)

Question 4

What is the structure of enzymes?

Answer 4

• globular protein
• have an active site which the substrate binds to
• active site has a specific shape which is determined by the enzymes tertiary structure

Question 5

What is an extracellular example?

Answer 5

• Amylase works outside cells in the human digestive system. Amylase is found in saliva and it catalyses the breakdown of starch into maltose in the mouth
• Trypsin catalyses the hydrolysis of peptide bonds (turns big polypeptides into smaller ones). Trypsin is produced by cells in the pancreas and secreted in the small intestine

Question 6

What is the activation energy?

Answer 6

A certain amount of energy needed before a reaction will start

Question 7

What do enzymes reduce?

Answer 7

The amount of energy that is needed to make reactions happen at a lower temperature. This speeds up the rate of reaction

Question 8

What is formed when a substrate binds to an enzymes active site?

Answer 8

An enzymes substrate complex is formed. This lowers the activation energy

Question 9

What are the reasons for the activation energy lowering?

Answer 9

1. If 2 substrate molecules need to be joined, attaching tot the enzyme holds them close together, reducing any repulsion between the molecules so they can bond more easily
2. If enzyme is catalysing a breakdown reaction, fitting into the active site puts a strain on bonds in the substrate. The strain means the substrate molecules breaks up more easily

Question 10

What is the lock and key model?

Answer 10

Enzymes only work with substrates that fit their active site with complementary shape. When the enzyme substrate complex is formed, it changes shape slightly, this locks the substrate in more tightly to the enzyme

Question 11

What is the induced fit model?

Answer 11

The substrate doesn’t only have to be the right shape to fit the active site, it has to make the active site change shape in the right way as well

Question 12

What happens to to the rate of reaction when temp increases?

Answer 12

Rate of reaction increases

Question 13

What factors affect enzyme activity?

Answer 13

• Temperature
• pH
• Enzyme concentration
• Substrate concentration

Question 14

How does the rate of reaction increase?

Answer 14

More heat = more kinetic energy = molecules move faster
This makes the substrate molecules more likely to collide with the active site of an enzyme

Question 15

What does the energy of the collisions increasing do?

Answer 15

Each collision is more likely to result in a reaction

Question 16

What is the optimum temperature for most reactions

Answer 16

37 degrees

Question 16

What happens if the temperature gets too high?

Answer 16

Reaction will stop because the increase in temp causes the enzyme molecule to vibrate. If they vibrate too much it can cause the bonds to hold the enzyme in shape to break/denatured

Question 16

When does the rate of reaction continue increase until?

Answer 16

The enzyme reaches optimum temperature

Question 17

What does the Q10 value for a reaction show?

Answer 17

How much the rate of reaction changes when the temperature is raised by 10 degrees

Question 18

What is the Q10 equation?

Answer 18

Q10 = R2 (rate at high temp) / R1 (rate at lower temp)

Question 19

What does the pH of an enzyme do?

Answer 19

Is the pH that the enzyme controlled reaction works fastest

Question 20

What happens if the pH goes above or bellow the optimum?

Answer 20

The H+ and OH- ions can break the ionic bonds and hydrogen bonds that hold the enzymes tertiary structure in place. This would change the active site of the enzyme and would become denatured

Question 21

What do most human enzymes work best at?

Answer 21

pH 7

Question 22

The higher the substrate concentration…?

Answer 22

The faster the reaction

Question 22

What happens due to the more enzyme molecules there are in a solution?

Answer 22

The more likely a substrate molecule will collide into one of them to form an enzyme substrate complex. This will increase the rate of reaction

Question 23

What happens if the substrate is limited?

Answer 23

There is no point adding more enzymes as it will have no further affect

Question 24

What does more substrate molecules mean?

Answer 24

More collisions between enzymes and a substrate. This is only true up until saturation point (all the active sites of enzymes are full) and adding more substrate will make no difference

Question 25

What is the limiting factor?

Answer 25

Enzyme concentration

Question 26

What do inorganic cofactors do?

Answer 26

• Work by helping the enzyme and substrate bind together
• don’t directly participate in the reaction so aren’t used up or changed in any way

Question 27

What are the 2 types of cofactors and coenzymes?

Answer 27

organic and inorganic

Question 28

What do organic cofactors (coenzymes) do?

Answer 28

• Participate in reactions and are changed by it
• often act as carriers moving chemical groups between different enzymes

Question 29

What is a prosthetic group?

Answer 29

A cofactor is closely bound to the enzyme

Question 30

What are enzyme inhibitors/what do they do?

Answer 30

Enzymes can be prevented by enzyme inhibitors (molecules that bind to the enzyme that they inhibit). There are 2 types of inhibitors: competitive and non-competitive

Question 31

What are competitive inhibitors?

Answer 31

• have similar shape to that of a substrate molecule
• compete with the substrate molecule to bind to the active site but no reaction takes place
• block the active site
• if increase conc of inhibitors, will take up most of the active sites and hardly any substrate will get to the enzyme
• increasing conc of substrate increases the ROR up to a point

Question 32

What are non-competitive inhibitors?

Answer 32

• bind to the enzyme away from the active site called the enzymes allosteric site
• causes enzyme to change shape so the substrate molecules can no longer bind to it
• don’t compete with a substrate so increase in conc of substrate will not make any difference (enzyme activity will be inhibited0

Question 33

What are reversible and non-reversible inhibition?

Answer 33

Inhibitors can be reversible (not bind permanently to an enzyme) or non-reversible (bind permanently to an enzyme). Which one they are depends on the strength of the bonds between the enzymes and the inhibitors

Question 34

What bonds does non-reversible inhibition have?

Answer 34

Strong covalent bonds so inhibitor can’t be removed easily so its non-reversible

Question 35

What bonds does reversible inhibition have?

Answer 35

Weak hydrogen bonds/ weak ionic bonds so the inhibitor can be removed so its reversible

Question 36

What can some medical drugs be used as?

Answer 36

Inhibitors

Question 37

What do metabolic poisons do?

Answer 37

Interfere with metabolic reactions (reactions that occur in cells), causing damage, illness or death

Question 38

Give examples of medical drugs

Answer 38

Antiviral drugs
Antibiotics

Question 38

Give examples of metabolic poisons

Answer 38

Cyanide
Malonate
Arsenic

Question 39

What is product inhibition?

Answer 39

• metabolic pathways are regulated by end-product inhibition
• metabolic pathway is a series of connected metabolic reactions
• product of the 1st reaction takes part in the 2nd and so on…
• each reaction is catalyzed by a different enzyme

Question 40

What is a metabolic pathway?

Answer 40

A series of connected metabolic reactions

Question 41

What is end-product inhibition?

Answer 41

• when final product in metabolic pathway inhibits an enzyme that acts earlier on in the pathway
• regulated the pathway and controls amount of end-product made

Question 42

Are product and end-product inhibition reversible or non-reversible?

Answer 42

Both are reversible

Question 43

What happens when the level of product starts to drop?

Answer 43

The level of inhibition will start to fall and the enzyme can start to function again (more product can be made)