8.1 Metabolism

Question 1

What is metabolism?

Answer 1

the sum of all reactions that occur within an organism to maintain life

Question 2

what is the activation energy (EA)

Answer 2

the amount of energy needed in order for a chemical reaction to occur

Question 3

how do enzymes speed up the rate of a biochemical reaction?

Answer 3

by lowering the activation energy

Question 4

what occurs when an enzyme binds to a substrate?(2)

Answer 4

it stresses and destabilises the bonds in the substrate
reducing the overall energy level of the substrate’s transitional stat (less energy is needed to convert it into a product)

Question 5

what are exergonic reactions?(2)

Answer 5

when reactants contain more energy than the products
and the free energy is released from broken bonds within a molecule

Question 6

what are endergonic reaction?

Answer 6

when the reactants contin less energy than the products
and free energy is lost to the system

Question 7

what type of reactions are exergonic reactions usually?

Answer 7

catabolic (breakdown) -> energy released from broken bonds within a molecule

Question 8

what type of reactions are endergonic reactions usually?

Answer 8

anabolic (build-up) -> energy required to synthesise bonds between molecules

Question 9

what is an enzyme inhibitor?

Answer 9

a molecule that disrupts the normal reaction pathway between enzyme and substrate

Question 10

what two things can enzyme inhibitors be?

Answer 10

competitive or non-competitive

Question 11

what do enzyme inhibitors do?

Answer 11

they prevent the formation of an enzyme-substrate complex and prevent formation of product

Question 12

what two things can enzyme inhibitions be?

Answer 12

• reversible
• irreversible
  (depending on the specific inhibitor being used)

Question 13

what occurs in a normal enzyme reaction? (5 steps)

Answer 13

1. substrate binds to enzyme (@ active site) to form enzyme-substrate complex
2. shape and properties of substrate and active site are complementary, resulting in enzyme specificity
3. when binding occurs, the active sit eundergoes a conformational change to optimally interact w/ the substrate (induced fit)
4. this conformational change destabilises chemical bonds within the substrate, lowering activation energy
5. as a consequence of enzyme interaction, the substrate is converted into product at an accelerated rate

Question 14

what does competitive inhibition involve? (3 steps)

Answer 14

1. involves a molecule other than substrate binding to the enzyme’s active site
2. inhibitor is structurally and chemically similar to the substrate (able to bind to active site)
3. the inhibitor blocks the active site and prevents substrate binding

Question 15

what can you do to reduce the effects of competitive inhibitors?

Answer 15

it is competitive, so the effects can be reduced by increasing substrate concentration

Question 16

what does non-competitive inhibition involve? (3 steps)

Answer 16

1. involves a molecule binding to a site other than the active site (allosteric site)
2. binding of the inhibitor to the allosteric site causes conformational change to enzyme’s active site
3. as a result, the active site and substrate no longer share specificity and substrate cannot bind

Question 17

why can increasing the substrate concentration not mitigate the non-competitive inhibitor’s effect?

Answer 17

as the inhibitor is not in direct competition with the substrate

Question 18

what can inhibitors be used in? (2)

Answer 18

medicine (treat disease)
agriculture (pesticides)

Question 19

what is an example of competitive inhibitor? and its use? (2)

Answer 19

relenza (via neuraminidase inhibitor)
for influenza

Question 20

what is an example of a non-competitive inhibitor?

Answer 20

cyanide (prevents ATP production via aerobic respiration)

Question 21

how does relenza work (a competitive inhibitor)? (3 steps)

Answer 21

1. virons are released from infected cells when viral enzyme (neuraminidase) cleaves a docking protein (hemagglutinin)
2. relenza competitively binds to neuraminidase active site and prevents cleavage of docking protein
3. so, virons are not released from infected cells, preventing the spread of influenza

Question 22

how does cyanide (non-competitive inhibitor) work?(3 steps)

Answer 22

1. binds to allosteric site on a carrier molecule that forms part of electron transport chain (cytochrome oxidase)
2. changing shape of active site, cytochrome oxidase can’t pass electron to final acceptor (oxygen)
3. electron transport chain cannot continue to function and ATP is not produced via aerobic respiration

Question 23

what is end-product inhibition or feedback inhibition?

Answer 23

it is a form of negative feedback by which metabolic pathways can be controlled

Question 24

what occurs in end-product inhibition? (3 steps)

Answer 24

1. the final product in a series of reactions inhibit an enzyme from an earlier step in the sequence
2. product binds to an allosteric site and temporarily inactivates the enzyme (via non-competitive inhibition)
3. the enzyme can no longer function, the reaction sequence is halted and the rate of product formation is decreased

Question 25

why does end-product inhibition occur? (3)

Answer 25

- to ensure levels of an essential product is always tightly regulated - if product level builds up, the product inhibits the reaction pathway and decreases the rate of further product formation - if the product level drops, the reaction pathway will proceed unhindered and rate of product formation will increase

Question 26

what is isoleucine?

Answer 26

an essential amino acid (no synthesised in humans) (found in cheese, eggs, chicken, fish)

Question 27

how does feedback inhibition ensure that isoleucine production does not cannibalise available stocks of theonine?

Answer 27

as isoleucine can bind to allosteric site on the enzyme and function as non-competitive inhibitor

Question 28

how can rate of reaction be measured?

Answer 28

Rate of reaction (s–1) = 1 / time taken (s)

Question 29

what two ways can time taken be measured to find rate of reaction?

Answer 29

measuring amount of product formed amount of substrate used

Question 30

why will increasing substrate levels increase the rate of reaction even when there is an inhibitor? (competitive inhibitors)

Answer 30

as it increases the likelihood of substrate colliding with enzyme instead of the inhibitor (Vmax can still be reached with higher substrate conc) (Vmax=maximum rate of enzyme activity)

Question 31

what effect will increasing the substrate concentrations have on the level of inhibition by non-competitive inhibitor? and why? (2)

Answer 31

no effect as there is no direct competition (Vmax is reduced)

Question 32

how can imbibition help to produce anti-malarial drugs?

Answer 32

by targetting the maturation and development of parasite in human and mosquito host coordinated by the specific enzymes - targeting enzymes for inhibition

Question 33

how can knowing the proteome of malaria help create medicine?

Answer 33

as the enzymes involved in parasitic metabolicm can be identified and targetted for inhibition

Question 34

hat can be used to identify potential enzyme inhibitors?

Answer 34

using a bioinformatic database of chemicals to identify potential enzyme inhibitor (once identifies it may be chemically modified to improve binding affinity and lower toxicity)

Question 35

what is another method which potential anti-malarial medications can be synthesised?

Answer 35

rational drug design

Question 36

what is involved in rational drug design? (2)

Answer 36

using computer modelling to invent a compound that will function as an inhibitor - using combinatorial chemistry a compound is synthesised that is complementary to the active sie of the target enzyme