Enzymes

Question 1

What are enzymes?

Answer 1

Enzymes are catalysts that alter the rate of a chemical reaction and are effective in small amounts.

Question 2

What are the characteristics of catalysts?

Answer 2

Catalysts are involved in but unchanged by the chemical reaction they catalyse.

Question 3

What additional features do enzymes have compared to general catalysts?

Answer 3

Enzymes are specific in their action and sensitive to changes in pH and temperature.

Question 4

What is the active site of an enzyme?

Answer 4

The active site is the small part of an enzyme molecule that binds with its substrate molecule.

Question 5

What is the composition of the active site?

Answer 5

The active site consists of just a few of the amino acid units that make up the enzyme molecule as a whole.

Question 6

What is intracellular enzyme action?

Answer 6

Enzyme action that occurs inside the cell where the enzyme is made.

Example: Cellular respiration catalyses the oxidation of substrates like glucose, releasing energy for ATP synthesis.

Question 7

What is extracellular enzyme action?

Answer 7

Enzyme action that occurs outside of cells.

Example: Amylase, made in salivary glands and pancreas, catalyses the digestion of starch in the mouth and duodenum.

Question 8

What is activation energy?

Answer 8

The minimum initial amount of energy required for a reaction to proceed

Question 9

What happens without activation energy?

Answer 9

Without activation energy, chemical reactions will not take place.

Question 10

How do enzymes affect activation energy?

Answer 10

Enzymes lower activation energy by forming enzyme-substrate complexes.

Question 11

What do enzymes enable?

Answer 11

Enzymes enable reactions which would need high temperatures in the laboratory to take place at body temperature.

Question 12

What determines the shape of an enzyme?

Answer 12

The shape of an enzyme is the result of its tertiary structure.

Question 13

What is the role of the active site in an enzyme?

Answer 13

The active site has a precise shape that is complementary to a particular substrate molecule.

Question 14

How do enzymes and substrates interact?

Answer 14

An enzyme binds with a substrate because their shapes fit together like a key fits into a lock.

Question 15

What does the ‘lock and key’ model suggest?

Answer 15

It suggests that the active site of an enzyme and its substrate are exactly complementary.

Question 16

What is the induced-fit hypothesis?

Answer 16

It shows that the active site and substrate are ONLY fully complementary after binding has taken place.

Question 17

What happens to the active site upon substrate binding?

Answer 17

The initial binding alters the shape (tertiary structure) of the active site.

Question 18

How does the substrate change during the reaction?

Answer 18

The shape of the substrate molecule alters, assisting the reaction to take place.

Question 19

Rate equation

Answer 19

Rate = change / time

Question 20

What is measured to determine the rate of an enzyme-controlled reaction?

Answer 20

The time taken for the appearance of product or disappearance of substrate.

Question 21

How can the appearance of product or disappearance of substrate be monitored?

Answer 21

By a change in colour of the reaction mixture.

Question 22

What is an example of an enzyme that catalyses a reaction?

Answer 22

The enzyme trypsin catalyses the breakdown of protein into peptides.

Question 23

How is the rate of reaction measured?

Answer 23

As the time taken for the reaction mixture to change.

Question 24

What are enzymes?

Answer 24

Enzymes are biological catalysts.

Question 25

What do enzymes do?

Answer 25

Enzymes speed up the rate of reactions without undergoing permanent changes themselves.

Question 26

Can enzymes be reused?

Answer 26

Yes, enzymes can be used repeatedly.

Question 27

What is the structure of enzymes?

Answer 27

Enzymes are globular proteins with specific shapes.

Question 28

What determines the active site of an enzyme?

Answer 28

The active site is due to the enzyme's tertiary structure, which is influenced by its primary structure.

Question 29

Where are enzymes found in the body?

Answer 29

Enzymes are found throughout the body, not just in digestion.

Question 30

What types of reactions do enzymes catalyze?

Answer 30

Enzymes can catalyze anabolic (making) reactions as well.

Question 31

Induced fit shows:

Answer 31

The active site is not complimentary to the substrate before it binds

Question 32

Induced fit provides the mechanism for:

Answer 32

- catabolic (breaking down) reactions, it suggests that putting strain on the bond is d the substrate lowers activation energy -anabolic (building up) reactions it means the substrates are in closer contact with each other, lowering activation energy

Question 33

What are the requirements for enzyme controlled reactions?

Answer 33

-successful collision at correct orientation with sufficient force to produced an enzyme-substrate-complex

Question 34

Factors affecting success of collisions( therefore rate of reaction)

Answer 34

-temp -pH -conc of substrate and enzymes -presence of inhibitors

Question 35

What is a competitive inhibitor?

Answer 35

A competitive inhibitor is a substance that combines with the active site of an enzyme, preventing its normal substrate from binding with it.

Question 36

What is a non-competitive inhibitor?

Answer 36

A non-competitive inhibitor is a substance that combines with some part of an enzyme molecule other than its active site.

Question 37

What effect does a non-competitive inhibitor have on an enzyme?

Answer 37

It causes a change in the shape of the enzyme molecule, which alters the shape of its active site.

Question 38

What happens to the substrate molecule in the presence of a non-competitive inhibitor?

Answer 38

The substrate molecule is no longer able to bind to the active site.

Question 39

Non competitive inhibition may be:

Answer 39

-reversible: breaking up the inhibitor-enzyme complex is possible -irreversible:breaking up the inhibitor-enzyme complex is not possible. Heavy metals such as arsenic and mercury are irreversible non competitive inhibitors which is why they are poisonous

Question 40

What is a metabolic pathway?

Answer 40

A sequence of reactions where a particular molecule is converted into another different one by way of a series of intermediate compounds ie. Molecule A —> molecule B —> molecule C —> etc

Question 41

Rate of reaction and time graph catalysed by enzyme (enzymes)

Answer 41

As time increases volume of product increases with the reaction slowing as the substrate is depleted or the enzyme becomes saturated v max is approached as all active sites become occupied (theoretical minimum rate of reaction)

Question 42

Rate of reaction and substrate concentration graph (enzymes)

Answer 42

As substrate concentration increases the initial rate of reaction increases because there is more substrate molecules available to bind to the active site of each enzyme molecule so more enzyme substrate complexes are formed

Question 43

Rate of reaction and enzyme concentration graph (enzymes)

Answer 43

The graph shows that the rate of reaction increases with enzyme concentration until a plateau is reached, where all enzymes are saturated with substrate

Question 44

Rate of reaction and temperature graph (enzymes)

Answer 44

The graph shows that the rate of reaction increases with temperature up to the enzyme’s optimum temperature, then rapidly decreases as the enzyme denatures.

Question 45

Rate of reaction and temperature uncatalysed (enzymes)

Answer 45

Rate of reaction gradually increases as temperature increases

Question 46

What happens to kinetic energy as temperature increases?

Answer 46

Increasing temperature increases the kinetic energy of molecules.

Question 47

How does increased kinetic energy affect the rate of reaction (RoR)?

Answer 47

It causes an increase in RoR due to more successful collisions occurring between the active site and substrate.

Question 48

What are the effects of more frequent and energetic collisions?

Answer 48

More frequent and energetic collisions lead to the formation of more enzyme-substrate complexes.

Question 49

What occurs after the optimum temperature is reached?

Answer 49

Increasing kinetic energy causes hydrogen bonds and hydrophobic interactions to break.

Question 50

What happens to the active site when kinetic energy continues to increase beyond optimum temperature?

Answer 50

The active site starts to lose its shape and the enzyme denatures.

Question 51

Is the change in enzyme shape reversible after denaturation?

Answer 51

This is an irreversible change.

Question 52

Difference between denaturation and deactivation

Answer 52

Denaturation a permanent change Deactivation is reversible

Question 53

Ways to measure reaction rate:

Answer 53

-measure product produced in fixed time OR time taken for substrate to disappear -calculate reaction rate (1/time) -take readings at a number time intervals -plot a time course for the reaction -calculate the initial rate of reaction

Question 54

What is the affect of increasing substrate concentration on an inhibitor

Answer 54

Increasing substrate conc affectively ‘dilutes’ the effect of the inhibitor. If enough substrate is added, the inhibitors less likely to collide with the enzymes active site

Question 55

Non competitive inhibitors usually permanently changes the enzyme the result…

Answer 55

… the same ROR can never be reached

Question 56

Reversible and non reversible inhibition:

Answer 56

-most competitive inhibitors have a reversible effect -reversible non- competitive inhibitors can be useful- they act as feedback in Hinton and control biological reactions to prevent the overproduction of certain molecules -non reversible, non competitive inhibitors can act as poisons ie. Cyanide

Question 57

What happens if the product of one reaction inhibits an enzyme preceding its formation?

Answer 57

The product will act as an inhibitor of the whole metabolic pathway.

Question 58

What is an allosteric inhibitor?

Answer 58

A substance that reversibly combines with the allosteric site