Module 2.1.4 Enzymes

Question 1

What are enzymes?

Answer 1

Globular proteins that have a specifically shaped active site formed in the tertiary structure

Question 2

What is a biological catalyst?

Answer 2

A molecule that speeds metabolic reactions without being used up/changed

Question 3

What types of reaction can enzymes catalyse?

Answer 3

Cellular level (e.g. respiration)
The whole organism

Question 4

How does an enzyme affect an organism?

Answer 4

Can affect structures & functions

Question 5

Are enzymes intracellular or extracellular?

Answer 5

Can be both

Question 6

What is an intracellular enzyme?

Answer 6

An enzyme that works inside cells

Question 7

What is an example of an intracellular enzyme & its function?

Answer 7

Catalase -> catalyses the breakdown of hydrogen peroxide into water & O2 as if it accumulates, it can become toxic

Question 8

What is an extracellular enzyme?

Answer 8

An enzyme that works outside cells

Question 9

What are some examples of extracellular enzymes & their functions?

Answer 9

Amylase -> found in saliva & secreted from the salivary glands, catalyses the hydrolysis of starch into maltose

Trypsin -> produced in the pancreas, found in the small intestine & catalyses the hydrolysis of peptide bonds in proteins

Question 10

How do enzymes speed up rate of reaction?

Answer 10

They lower the activation energy to speed it up

Question 11

What is the activation energy?

Answer 11

The minimum amount of energy required to start a reaction

Question 12

How do enzymes reduce activation energy?

Answer 12

Via the formation of enzyme-substrate complexes

Question 13

What is an enzyme-substrate complex?

Answer 13

When the substrate fits into the active site putting a strain on their bonds (which are needed to break down) & repulsion is reduced between substrates which need joining allowing bonds to break/form more easily

Question 14

What is the active site?

Answer 14

A cleft/depression specifically shaped by the tertiary structure

Question 15

What are the 2 mechanism models of enzyme activity?

Answer 15

The lock & key fit model
The induced fit model

Question 16

What is the lock & key model?

Answer 16

A model of enzyme activity suggests that a substrate fits into the specifically shaped active site due to its complimentary shape allowing an exact fit

Question 17

What is the induced fit model of enzyme activity?

Answer 17

A newer model of the lock & key model suggesting the active site changes shape slightly to fit the substrate more closely but the substrate must be near to being exactly complementary

Question 18

What are the similarities between the 2 models?

Answer 18

The substrate fits into the active site to form an enzyme substrate complex, reaction occurs & chemically changes the substrate to form an enzyme product complex, then the products are released

Question 19

What are the 4 factors affecting enzyme activity?

Answer 19

Temperature
PH
Enzyme concentration
Substrate concentration

Question 20

How does temperature affect enzyme activity?

Answer 20

As temperature increases, so does the kinetic energy of the molecules. This increases the rate of successful enzyme-substrate collisions and therefore the rate of reaction. Once temperature goes above optimum, the rate of reaction decreases as the molecules vibrate too much and break the bonds holding the enzymes tertiary structure in place. This causes the active site to change shape & therefore denatures the enzyme

Question 21

How does PH affect enzyme activity?

Answer 21

Above & below the optimum pH of the enzymes, H+ & OH- ions in acids & alkalis disrupt the ionic & hydrogen bonds holding the tertiary structure in place. This causes the active site to change shape & therefore denatures the enzyme

Question 22

What is the temperature coefficient?

Answer 22

Q10 -> how much the rate of reaction changes when the temperature is raised by 10 degrees

Q10 + R2(rate at higher temp)/R1 (rate at lower temp)

Question 23

How does enzyme concentration have an effect on enzyme activity?

Answer 23

As the concentration increases, the amount of molecules present in the reaction increases. This causes more successful enzyme-substrate collisions which increases the rate of reaction.

Question 24

What happens when there is limited substrate & the enzyme concentration is further increases?

Answer 24

There will be no further effect as it will be unused

Question 25

How does substrate concentration have an effect on enzyme activity?

Answer 25

As concentration increases, so does the number of molecules present in the reaction. This increases the likelihood of sucessful enzyme-substrate collisions & therefore the rate of reaction

Question 26

What happens if there is limited enzyme concentration & an increasing substrate concentration?

Answer 26

There will be no further effect as the enzyme will reach saturation point which, if left unchanged with decrease the rate of reaction as the substrate is used up

Question 27

What is the saturation point?

Answer 27

The point that all the active sites are occupied

Question 28

What is a cofactor?

Answer 28

A non-proteins substance bound to some enzymes which helps the enzyme & substrate bind together but doesnt directly participants in the reaction (remains unchanged)

Inorganic molecules/ions

Question 29

What is an example of a cofactor in an enzyme?

Answer 29

Cl- in amylase

Question 30

What is a coenzyme?

Answer 30

Organic cofactors which participate in the reaction & are changed by it, allowing them to act as carriers of different chemical groups between different enzymes being continually recycled during this process

Question 31

What is an example of a coenzyme?

Answer 31

Vitamins

Question 32

What are prosthetic groups?

Answer 32

A cofactor that is tightly bound to the enzyme

Question 33

What is an example of a prosthetic group?

Answer 33

Heme -> haemoglobin

Question 34

What are the 4 different types of inhibitors?

Answer 34

Competitive
Non-competitive
Reversible
Irreversible

Question 35

What are the characteristics of competitive inhibitors?

Answer 35

Similarly shaped to the substrate
Compete with the substrate to bind to the active site, blocking it so no enzyme-substrate complex can form so there is no reaction
If substrate concentration is greater than the inhibitor concentration, rate of reaction with increase until all non-inhibited enzymes are saturated

Question 36

What are the characteristics of non-competitive inhibitors?

Answer 36

• Different shape to the substrate
• Doesn’t compete with the substrate & instead binds to the allosteric site on the enzyme, which causes a reaction & the active site to change shape so the substrate can no longer fit & an enzyme-substrate complex cannot form
• Increasing the substrate concentration wont effect the reaction rate as the substrate is no longer complementary to the active site

Question 37

What are the characteristics of reversible inhibitors?

Answer 37

Removed easily
Held by weak hydrogen/ionic bonds

Question 38

What are the characteristics of irreversible inhibitors?

Answer 38

Cannot be removed easily
Held by strong covalent bonds

Question 39

What are some examples of enzymes inhibitors as metabolic poisons?

Answer 39

Cyanide -> inhibits cytochrome C oxidase
Malonate -> inhibits succinate dehydrogenase
Arsenic -> inhibits pyruvate

All involved in respiration reactions, when inhibited cells cannot respire = death

Question 40

What are some examples of enzyme inhibitors as asmedicinal drugs?

Answer 40

Antiviral drugs -> reverse transcriptase inhibitors (inhibits reverse transciptase) -> virus cannot replicate
Antibiotics -> penicillin -> inhibits transpeptidase -> prevents proteins synthesis in the bacterial cell walls which weakens the cells well so it will burst due to osmotic pressure not
being regulated

Question 41

What are inactive precursors?

Answer 41

Molecules that are unable to function which prevent them causing damage to cells

Question 42

What is an example of inactive precursors?

Answer 42

Some protease enzymes -> synthesised as an inactive precursor to stop them damaging proteins in the cells they are made

Question 43

Can an inactive precursors turn back into an enzyme?

Answer 43

Yes as when the inhibiting part of the precursor is removed the enzyme becomes active again

Question 44

What is a metabolic pathway?

Answer 44

A series of connected metabolic reactions in which the product of the first reaction takes part in the second reaction and so on with each reaction being catalysed by a different enzyme

Question 45

What is production inhibition?

Answer 45

When an enzyme is inhibited by the product of the reaction it catalyses which is reversible

Question 46

What is end product inhibition?

Answer 46

When the final product in a metabolic pathway inhibits an enzyme catalysing a reaction from earlier on in the pathway

Question 47

What is positive about end product inhibition?

Answer 47

It is a good way of controlling the amount of end product produced as it is reversible (when the level of product falls the level of inhibition will fall and the enzyme can function again to produce more product)