enzymes

Question 1

what are enzymes?

Answer 1

Enzymes are biological catalysts, made of protein, that speed up metabolic reactions without being used up themselves

Question 2

what type of protein are enzymes

Answer 2

globular proteins

Question 3

In the laboratory the activation energy required for a particular reaction is often attained by heating. Why would this be unsuitable for the reactions that take place in your body cells?

Answer 3

Cannot have higher body temperatures than 37oC because it would denature protein molecules e.g. enzymes, structural proteins.

Question 4

what do enzymes do to activation energy?

Answer 4

• Enzymes lower the activation energy required (activation energy) to overcome the energy barrier
• This reduction in activation energy enables reactions to take place at the rapid rate necessary to sustain life

Question 5

What is the ‘activation energy’ of a reaction?

Answer 5

The activation energy is the energy barrier
that has to be overcome before the reaction
can happen

Question 6

describe enzyme action

Answer 6

• Enzymes act on substrates
• The substrate complementary shape fits and binds into a special site on the enzyme called the active site
• This forms an enzyme substrate complex

• The reaction changes the shape of the substrate, which lowers the activation energy. It becomes an enzyme product complex, so the product(s) no longer fit the active site and are released

Question 7

what is metabolism

Answer 7

• Metabolism is the name for all the chemical reactions occurring in the cells of living organisms. Metabolic reactions are classified into two types:
• Anabolic – building up molecules
• Catabolic – breaking down molecules

Question 8

Which of the following enzyme controlled reactions in plant cells is anabolic and which is catabolic?
a. the formation of maltose from starch?
b. The synthesis of starch from glucose-1-phosphate?

Answer 8

a. catabolic
b. anabolic

Question 9

what is enzyme specificity?

Answer 9

• Enzyme specificity is the term used to describe the fact that
each enzyme is specific to a particular substrate.
• Enzyme specificity is due to only one substrate (or a very small number) being an exact complementary shape to the active site

Question 10

why is being globular proteins important?

Answer 10

• Being globular proteins, enzymes are able to form the wide range of 3D shapes necessary to facilitate enzyme specificity.

Question 11

describe the lock and key model

Answer 11

• This theory was put forward to explain why enzymes are specific.
• It proposes that the active site of an enzyme has exact match and is a complementary shape (like a lock) into which the substrate molecule (the key) fits exactly.

Question 12

describe the induced fit theory

Answer 12

• This is a more updated version of the lock and key hypothesis.
• It suggests that the active site is not an exact fit for the substrate molecule but very closely matches the shape of the substrate. It is complementary once binding occurs

Question 13

in the induced fit theory what can the enzyme do?

Answer 13

• The active site can mould itself around the substrate, forming a precise fit.
• The active site is therefore flexible and as it changes shape to fit the substrate

• The enzyme is able to put pressure on the substrate, breaking particular bonds and therefore lowering the activation energy required for the
reaction to take place.

Question 14

what are co factors?

Answer 14

Cofactors are non protein substances that enzymes require in order to function.

Question 15

what are co enzymes?

Answer 15

• A particular type of cofactor.
• They are non protein, organic molecules
necessary for enzyme action
• Important in respiration and photosynthesis
• E.g NAD and FAD act as hydrogen acceptors in
respiration
THEY ARE NOT PERMANENTLY ATTACHED

Question 16

Chloride is a cofactor of amylase, the enzyme that breaks down starch into maltose molecules.
• What would happen to the production of maltose if amylase had to function in the absence of chloride ions?

Answer 16

maltose would decrease

Question 17

factors which effect enzyme activity

Answer 17

temperature
pH
substrate concentration
enzyme concentration

Question 18

describe affects of substrate concentration

Answer 18

• At lower concentrations of substrate the rate increases in direct proportion to the substrate concentration i.e. enzyme activity increases as substrate concentration increases, substrate is the limiting factor.

Question 19

Only a small amount of enzyme is needed to catalyse a lot of substrate. Why?

Answer 19

Enzymes are used over and over again and so function at very low concentrations.

Question 20

affects of enzyme concentration

Answer 20

• If number of substrates (substrate concentration) is kept at a fixed rate
• level of enzyme is increased
• enzyme activity will also increase

• As more enzymes are available, the rate increases up to a limit, by which time the number of substrate molecules becomes limiting

Question 21

what is an adaptation to increase enzyme availability

Answer 21

the extensive infolding of mitochondrial cristae to increase the surface area of the inner membrane, and consequently the number of respiratory enzymes located on the membrane.

Question 22

affects of temperature

Answer 22

Increasing the temperature by heating increases the rate of most chemical reactions because the molecules have more kinetic energy and move around faster. There is a greater probability of more successful collisions between enzymes active site and substrates. Therefore more enzyme-substrate complexes are formed and hence the rate of reaction increases.

Question 23

describe denaturing

Answer 23

The shape of the active site has been permanently changed and it is no longer complementary in shape to the substrate molecule.

Question 24

affects of pH

Answer 24

• Enzymes have an optimum pH at which the rate of reaction is fastest.
• At this specific pH the shape of the active site best facilitates the formation of an enzyme-substrate complex. Most enzymes work best at a pH between 6 and 8, a range that corresponds to the general acidic level of cells and blood

Question 25

what are inhibitors

Answer 25

• Inhibitors are substances that bind to enzymes and decrease their enzyme action.
• They reduce enzyme activity by directly or indirectly affecting the functioning of the active site.

Question 26

competitive inhibitors

Answer 26

Competitive inhibitors competes with the usual substrate for the active site of the enzyme molecule.
• They are similar in shape to the substrate molecule.
• *The inhibitor is complementary in shape to enzyme active
site
• *The inhibitor’s shape allows it to fit into the active site, preventing the substrate from fitting in and thus preventing the formation of an enzyme-substrate complex.
• The rate of reaction is therefore reduced.
• If the inhibitor is removed the active sites will all be free to combine with substrate molecules

Question 27

non competitive inhibitors

Answer 27

• Non-competitive inhibition is when the
inhibitor attaches itself to a part of the enzyme other than the active site
• The presence of the non competitive inhibitor leads to the active site changing shape so it is no longer complementary to the substrate and can no longer bind with it.

Question 28

allosteric enzymes

Answer 28

Allosteric enzymes
• Enzymes that have a second site where (non-substrate) molecules can attach are described as allosteric enzymes.
• This is important in negative feedback.
• Note: this second site is not an active site!

Question 29

Heavy metal ions such as Hg+ (mercury), Ag+ (silver) and As+ (arsenic), alter the tertiary structure of a protein by breaking its disulfide bonds. What type of enzyme inhibitor would they be?

Answer 29

Non competitive (and permanent)

Question 30

how are enzymes biomarkers for disease

Answer 30

During injury or disease of an organ, the damaged tissue will release its enzymes, including those specific to the organ

Question 31

how can enzymes be monitored?

Answer 31

Enzymes can be monitored in blood, urine and sputum

Question 32

elastase

Answer 32

Elastase is an enzymes released by white blood cells (called polymorphs) during respiratory infection (e.g pneumonia)

• Elastase breaks down bacterial pathogens and is part of the immune response.
• Elastase also hydrolyses the structural protein elastin within the within the alveolar walls of the lung.
• Elastin gives the lung their elastic stretch and recoil property during exhalation.

Question 33

what is the elastase inhibitors and its effect?

Answer 33

• Normally elastin is not broken down as the elastase inhibitor alpha-a-antitrypsin (A1AT) prevents elastase activity after the infection has been cleared

Question 34

what is the effects of cigarette smoke on elastase

Answer 34

Cigarette smoke causes too much elastase to be released in the lungs and there is not enough alpha-a-antitrypsin present (cigarette smoke also inhibits the synthesis of alpha-a-antitrypsin). Therefore, the elastin in the alveoli is broken down eventually resulting in elastase-induced emphysema

Question 35

enzyme inhibitors as therapeutic drugs

Answer 35

• Many therapeutic drugs (a drug which relates to the healing of a disease) are enzyme inhibitors.
• The drug inactivates an enzyme associated with a particular medical condition though not with normal physiological activity

Question 36

how can enzymes be effective drugs?

Answer 36

have high specificity
work at low doses

Question 37

ACE

Answer 37

ACE inhibitors used to treat high blood pressure.
• They work by inhibiting the enzymes that constrict the blood vessels to then lower the blood pressure

Question 38

penicillin

Answer 38

Is an antibiotic that inhibit the enzymes involved in the formation of bacterial cell walls

Question 39

action of antibiotics

Answer 39

• The bacteria are killed as the cell bursts, as it cannot
resist osmotic pressure due to a weakened cell wall.

Question 40

antiviral drugs

Answer 40

inhibit the DNA/RNA polymerases essential in viral replication