Module 2 - Enzymes

Question 1

how can the rate of metabolic activity be controlled?

Answer 1

different steps of a reaction are controlled by different enzymes regulating the rate and yield of product formation

Question 2

how can enzymes be activated?

Answer 2

with a cofactor

Question 3

how can enzymes be inactivated?

Answer 3

with an inhibitor

Question 4

what is competitive inhibition?

Answer 4

a molecule of similar shape will bind to enzyme preventing the complimentary substrate from binding and therefore preventing the reaction
the substrate and non-substrate will complete with each other to bind to the active site reducing the number of enzyme-substrate complexes from forming slowing the rate

Question 5

what does the degree of inhibition depend on?

Answer 5

relative concentration of substrate, inhibitor, and enzyme

Question 6

how doe competitive inhibitors work?

Answer 6

1- molecule of similar shape will bind to the enzyme preventing the complimentary substrate from binding
2- the prevents the enzyme catalysing the reaction
3- the enzyme cannot carry out its function and is said to be inhibited

Question 7

how do competitive inhibitors impact the Vmax?

Answer 7

they reduce the rate of reaction for a given conc. of substrate HOWEVER they do not change the Vmax of the enzyme it inhibits
= if substrate conc. is increased enough then there will be more substrate then inhibitor and so the Vmax can still be reached

Question 8

what are examples of competitive inhibitors?

Answer 8

> statins are CIs used in the synthesis of cholesterol - they’re regularly prescribed to help reduce blood cholesterol conc. as high levels can result in heart disease
aspirin irreversibly inhibits the active site of COX enzymes preventing the synthesis of the protein responsible for producing pain and fever

Question 9

what is a non-competitive inhibitor?

Answer 9

does not compete with the substrate for the active site as it binds elsewhere at the allosteric site

Question 10

how does non-competitive inhibition work?

Answer 10

1- inhibitor binds to enzyme at any location other then the active site = called the allosteric site
2- this inhibition caused the tertiary structure of the enzyme shape = active site changes shape
3- results in active site no longer having a complimentary substate = enzyme-substrate complex not able to form
4- enzyme cannot carry out its function and is inhibited

Question 11

what effect do non-competitive inhibitors have on rate of reaction?

Answer 11

increasing conc. of enzyme or substrate will not overcome the effects of inhibition
increasing conc. of inhibitor will decrease the rate of reaction further as more active sites become unavailable

Question 12

example of an irreversible non-competitive inhibitor?

Answer 12

irreversible inhibition cannot be removed from the area of enzyme they’re attached to
they’re often very toxic (not always)
Proton Pump inhibitors (PPI) are used to treat long term indigestion as they irreversibly block the enzyme system responsible for secreting H into the stomach reducing the production of excess acid - if left untreated leads to formation of stomach ulcers

Question 13

what is end-prouduct inhibition?

Answer 13

term used for enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to they enzyme that produces it

Question 14

how does end product inhibition act as a control mechanism?

Answer 14

it is an example of negative feedback
excess products are not made and resources are not wasted

Question 15

what type of inhibition is end product inhibition?

Answer 15

non-competitive reversible inhibition

Question 16

what is a cofactor + coenzyme?

Answer 16

they are non-protein ‘helper’ components that are required by some enzymes to help carry out their function
(if the cofactor is an organic molecule its called a coenzyme)

Question 17

how are inorganic cofactors obtained?

Answer 17

via the diet as minerals e.g iron, calcium, chloride

Question 19

what is end product inhibition?

Answer 19

term used for the enzyme inhibition that occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it
they’re en example of negative feedback

Question 20

how do end product inhibitors act as control mechanisms?

Answer 20

excess products are not made and resources are not wasted

Question 21

what are end product inhibitors an example of?

Answer 21

non-competitive reversible inhibitors

Question 22

what are cofactors and coenzymes?

Answer 22

non-protein ‘helper’ component that are required by some enzymes to help them cary out their function
if the cofactor is an organic molecule then its a coenzyme

Question 23

why is the function of coproduction/coenzymes?

Answer 23

they may transfer atoms/groups from one reaction to another in a multi-step pathway
they may form part of the enzymes active site

Question 24

how are inorganic cofactors obtained?

Answer 24

via the diet as minerals
e.g iron, calcium, chloride, zinc ions

Question 25

inorganic cofactor example:

Answer 25

enzymes amylase (catalyses the breakdown of starch) contains Cl- ions necessary for the formation of a correctly shaped active site

Question 26

how are organic coenzymes derived?

Answer 26

via vitamins found in the diet

Question 27

examples of a coenzyme:

Answer 27

vitamin B3 used to synthesise NAD = coenzymes responsible for the transfer of H between molecules in respiration
also used to synthesise NADP which plays a similar role in photosynthesis

vitamin B5 is used to make coenzyme A which is essential for the breakdown of fatty acids and carbohydrates in respiration

Question 28

how are prosthetic groups cofactors?

Answer 28

they’re required by certain enzymes to carry out their catalytic function

Question 29

what’s the difference between prothetic groups and normal cofactors?

Answer 29

prosthetic groups are tightly bound and form a permanent feature on the enzyme/protein
normal coenzymes are temporarily bound in order to activate them

Question 30

what is precursor activation?

Answer 30

enzymes are produced in an inactive form = precursor enzymes
to activate them they often need to undergo change to their 3* shape - particuarlly at the active site - to be activated

Question 31

how is activation of a precursor enzyme achieved?

Answer 31

by the addition of a cofactor

Question 32

what is the protein called before activation?

Answer 32

apoenzyme

Question 33

what is the protein called after activation?

Answer 33

once cofactor is added and the enzyme is activated it is called a holoenzyme