ENZYMES

Question 1

What is an enzyme?

Answer 1

Biological catalysts that speed up the rate of chemical reactions without getting used up by lowering the activation energy of a reaction.

Question 2

What are enzymes made from?

Answer 2

Globular proteins

Question 3

What is Activation Energy (Ea)?

Answer 3

The minimum amount of energy required for a reaction to occur.

Question 4

What is the affect of enzymes upon the Ea?

Answer 4

Lowers Ea allowing the reaction to occur much more easily at a relatively low temp.

Question 5

What is metabolism?

Answer 5

Chemical reactions of an organism

Question 6

What is catabolism?

Answer 6

Breakdown reactions
-binding of substrate induces a conformational change in shape of active site that distorts substrate molecule thus facilitating the breaking of a particular bond

Question 7

What is anabolism?

Answer 7

Build-up reactions

-substrate molecules held on the active site and orientated in a position to facilitate bonding between them.

Question 8

Explain the Lock and Key Model/Enzyme specificity

Answer 8

1. Active site of an enzyme has a specific complimentary shape (like a lock) into which the substrate (the key) fits into exactly to form the enzyme-substrate complex.
2. Following the reaction, the product leaves the active site of the enzyme as the shapes are no longer complimentary.
   - this allows the enzyme to be used again

Question 9

How do enzymes facilitate specificity

Answer 9

Each enzyme is specific to a particular substrate (two have a complimentary shape) and follow th lock and key model
-as enzymes are globular, enzymes are able to form a range of 3D shapes needed to facilitate the lock and key model.

Question 10

Explain the Induced Fit Model.

Answer 10

1. Shape of active site of enzyme is not quite complimentary to shape of substrate
2. As substrate begins to bind to enzyme, active site moulds itself around substrate making the two complimentary + forming enzyme-substrate complex
3. Following the reaction, the active site returns to its pre-reaction shape causing the products to leave the active site. (shapes no longer complimentary).

Question 11

What are cofactors?

Answer 11

Non-protein molecules that enzymes require in order to function (e.g Mg2+, Ca2+ and Fe3+)

Attach to enzyme and change the active site enabling substrate to bind and allowing the reaction to occur.

Question 12

What are prosthetic groups?

Answer 12

Type of cofactor that is covalently bonded to enzyme and is integral to function

E.g Haem is a prosthetic group in catalase enzyme

Question 13

What are coenzymes?

Answer 13

Type of cofactor that is not permanently attached to enzyme but is integral to function.

Mostly organic molecules
-NAD and FAD act as Hydrogen acceptors in respiration

Question 14

What is the effect of substrate concentration on enzyme activity?

Answer 14

1. As substrate conc. increases, enzyme activity increases
   - Greater conc. substrate molecules increases number of successful collisions with active site of enzyme therefore rate of formation of enzyme-substrate complexes (hence activity) increases.
2. at very high substrate conc., an increase does not cause increase in activity
   - All active sites occupied at any one moment (enzymes fully employed)

Question 15

Effect of enzyme concentration on enzyme activity?

Answer 15

1. As enzyme conc. increases, enzyme activity increases
   -Greater conc. enzyme molecules increases number of successful collisions with substrate molecules therefore rate of formation of enzyme-substrate complexes (hence activity) increases.
2. at very high substrate conc., an increase does not cause increase in activity
   -Substrate is limiting factor
   -enzyme is in excess
   N.B- in living organisms, substrate rarely limiting

Question 16

Effect of pH on enzyme activity?

Answer 16

Greater the pH is from optimum, the greater the degree of disruption to ionic bonds in enzyme which causes the shape of the active site to change and enzyme to denature
-Active site no longer complimentary to substrate causing activity to fall.

Question 17

Effect of temp. on enzyme activity?

Answer 17

1. At low temp., an increase in temp. causes an exponential increase in enzyme activity.
   - increase in temp. causes more KE for the successful collision of enzyme and substrate therefore rate of formation of enzyme-substrate complexes (hence activity) to increase.
2. at optimum temp., enzyme activity at highest
   - greatest rate of enzyme-substrate complex formation
3. Temp. above optimum, H-bonds in enzyme which causes the shape of the active site to change and enzyme to denature

Question 18

Why do optimum temp. of enzymes differ?

Answer 18

Plant enzymes lower optimum than mammalian enzymes

-soil temp. lower than environmental temp. + allow more growth in spring

Question 19

What are enzyme inhibitors?

Answer 19

Substances that interfere with enzyme action

- reduce enzyme activity by directly/indirectly affecting active site function

Question 20

what is competitive inhibition?

Answer 20

inhibitor has complementary shape to the active site of the enzyme.
Inhibitor competes with substrate to fit into the active site of enzyme and blocks it, reducing the rate of formation of enzyme-substrate complexes (hence activity).
N.B- Reversible

Question 21

what is the affect of conc. on competitive inhibition?

Answer 21

substrate conc. > inhibitor conc. = no affect
- most of active sites occupied by substrate
inhibitor conc. > substrate conc. = affect
- most of active sites occupied by inhibitor, therefore enzyme activity decreased

Question 22

Non-competitive inhibition; irreversible inhibitors

Answer 22

permanently damages enzyme active site (denature) therefore substrate and active site no longer complimentary causing rate of enzyme-substrate complexes (hence enzyme activity) to decrease.

E.g- Cyanide non-reversible inhibitor of respiratory enzyme cytochrome oxidase

Question 23

Allosteric enzymes

Answer 23

enzymes that have a second site which non-competitive inhibitors can attach to to change the shape of the main active site therefore reducing rate of enzyme activity as active site and substrate no longer complimentary.

Inhibitor may leave allowing main active site to regain its catalytic shape

inhibitors used in negative feedback

Increasing conc. of substrate does not have an affect but number of functioning enzymes have been reduced.

Question 24

Angiotensin Converting Enzyme (ACE)

Answer 24

• Inhibitors used to treat high blood pressure + other cardiovascular diseases
• Helps prevent high blood pressure by Inhibiting enzyme that leads to a constriction of blood vessels which can cause high blood pressure.
o High blood pressure is a significant factor in many cardiovascular diseases.

Question 25

Penicillin (and other antibiotics)

Answer 25

• Inhibits enzymes involved in (peptidoglycan) cell wall formation in bacteria

Question 26

Antiviral drugs

Answer 26

• Inhibit DNA/RNA polymerase

o Essential in viral replication

Question 27

Current research

Answer 27

• Enzyme inhibitors can be used in the treatment of cancer
• Identifying the shape of active site of enzymes involved in disease progression
o Can model and develop inhibitors with a complimentary shape to block active sites.

Question 28

why does cutting lettuce with a knife cause enzymes to catalyse faster than tearing with hand

Answer 28

Cutting results in destruction of cells, so that more enzyme is released;
whereas tearing leaves cells intact/breaks the tissue along cell walls;

Question 29

For enzyme inhibitors to be effective as therapeutic drugs?

Answer 29

1) Specific- only bind to enzymes that cause the disease or metabolic pathways may be affected.
- most inhibitors target the complementary and specific active site of the enzyme

2) Be able to work at low doses
- Inhibitors may be toxic at high levels

Question 30

how can enzymes be used as biomarkers of disease?

Answer 30

many diseases involve changes in the amounts of biological molecules e.g enzymes in affected tissue

Measurement of these amounts (biomarkers) are useful in diagnosis and monitoring of disease progression

Differences in the levels of enzyme indicate a disease

Question 31

What specimens can enzyme levels be tested?

Answer 31

Blood, urine or sputum/phlegm

Question 32

What are biosensors?

Answer 32

Devices that use biological material (Enzymes/antibodies) in the detection of a substance of interest.

usually quantitative to identify the conc. of substance of interest.