enzymes

Question 1

what is anabolism?

Answer 1

synthesis of molecules

Question 2

what is catabolism?

Answer 2

breakdown of molecules

Question 3

REDDEH

what are the 6 properties of enzymes

Answer 3

R - regulated by activators
E - effective in small amounts
D - denatured by heat
D - denatured by pH
E - extremely efficient
H - high degree of specificity

Question 4

what are the four categories of amino acid residues?

Answer 4

catalytic amino acid residues
binding amino acid residues
structural amino acid residues
non-essential amino acid residues

Question 5

what are the three different cofactors?

Answer 5

inorganic metal ions
coenzymes
prosthetic groups

Question 6

what are the four factors affecting an enzyme reaction?

Answer 6

substrate concentration
enzyme concentration
temperature
pH

Question 7

what is Vmax

Answer 7

the maximum rate at which an enzyme is able to perform the reaction

Question 8

what is Km

Answer 8

the affinity of the enzyme for its substrate

Question 9

do reactions with competitive inhibitors reach the same Vmax as those without?

Answer 9

yes

increased substrate conc reduces effect of inhibition as substrate and inhibitor are in direct competition for active site of enzymes. more substrate = more chance substrate can out-compete inhibitor

Question 10

do reactions with non-competitive inhibitors reach the same Vmax as those without?

Answer 10

no

non-competitive inhibitor changes 3d conformation of active site = substrate unable to bind = some enzymes are rendered inactive = lower vmax
substrate & inhibitor are not in direct competition so increased substrate conc doesnt affect inhibition

Question 11

what is an allosteric site?

Answer 11

an allosteric site is a site other than the active site

Question 12

what is the difference between allosteric inhibition and non-competitive inhibition?

Answer 12

in allosteric inhibition, the inhibitor binds to a multimeric enzyme.
in non-competitive inhibition, the inhibitor binds to a monomeric enzyme

allosteric inhibition is a type of non-competitive inhibition

Question 13

what are the differences between reversible and irreversible inhibition?

Answer 13

1. reversible: binded via weak non-covalent bonds. irreversible: binded via covalent bonds
2. reversible: binded temporarily and doesn’t cause permanent damage when removed. irreversible: causes permanent damage to enzyme when removed

Question 14

what is end product inhibition?

Answer 14

the end-product of a metabolic pathway acts as an inhibitor on the enzymes controlling the preceding steps of the pathway

Question 15

how does low substrate concentration affect the rate of reaction?

Answer 15

at low substrate concentrations, increase in substrate concentration results in a proportional increase in rate of reaction.
1. not all active sites of enzymes are occupied
2. rate is limited by concentration of substrate
3. increased substrate concentration = increased frequency of effective collisions = increased number of es complexes formed per unit time = increased products formed per unit time = increased rate of reaction

Question 16

how does high substrate concentration affect the rate of reaction?

Answer 16

at high substrate concentration, a point will be reached where any further increase in substrate concentration does not result in an increase in rate of reaction
1. active site of every enzyme is occupied any any given moment
2. rate is limited by saturation of enzyme active sites — substrate concentration is no longer limiting, enzyme concentration is limiting
3. further increase in substrate concentration doesn’t lead to increase in rate of reaction
4. rate of reaction can only increase with the addition of enzyme

Question 17

how does low enzyme concentration affect rate of reaction?

Answer 17

at low enzyme concentration, an increase in enzyme concentration results in a proportional increase in the rate of reaction.
1. increase enzyme concentration = more active sites
2. rate of reaction is limited by concentration of enzyme
3. increased frequency of collisions between substrate and active sites
4. more es complexes formed per unit time = increased amount of product formed per unit time = increased rate of reaction

Question 18

how does high enzyme concentration affect rate of reaction?

Answer 18

at high enzyme concentration, a point will be reached when any further increase in enzyme concentration does not lead to an increase in rate of reaction.
1. enzyme concentration is no longer a limiting factor — substrate concentration is limiting instead
2. rate of reaction can only be increased with the addition of substrate

Question 19

how does low temperatures (before optimum) affect rate of reaction?

Answer 19

1. at low temperatures, enzymes are inactivated
2. increased temp = increased kinetic energy = increased frequency of effective collisions = increased formation of es complexes = more product formed = increased rate of reaction

Question 20

how does optimum temperature affect rate of reaction?

Answer 20

enzyme activity is the highest at optimum temperature
1. highest number of es complexes formed per unit time
2. most amount of product formed per unit time
3. rate of reaction highest

Question 21

how does high temperatures (beyond optimum) affect rate of reaction?

Answer 21

1. decrease in rate of reaction despite increase in frequency of collisions
2. thermal agitation of enzymes disrupt hydrogen bonds, ionic bonds etc that stabilise the 3d conformation of the protein
3. loss in 3d conformation of enzyme & active site = no longer complementary to substrate
4. enzyme is denatured and loses its catalytic function
5. frequency of effective collisions decreases and rate of formation of es complex drops = less product is formed per unit time

Question 22

how do changes in pH affect the enzyme overall?

Answer 22

changes in ionisation of amino acids disrupted the ionic/hydrogen bonds that maintain the 3d conformation of the enzyme, denaturing the enzyme

Question 23

how do changes in pH affect different amino acid residues (structural, binding & catalytic)?

Answer 23

1. structural: conformation of active site no longer complementary to substrate = no es complexes formed
2. binding: substrate cannot be held in its correct orientation in active site for catalysis to occur
3. catalytic: R groups on catalytic amino acid residues no longer possess the correct ionisation/charge to catalyse the required reaction

Question 24

what are some advantages of metabolic pathways?

Answer 24

1. biochemical reactions can proceed without accumulation of products in the cells
2. reactants may be modified to release energy in controlled amounts
3. portioning of cell metabolites are finely balanced among different pathways
4. pathways are arranged such that the product of one reaction is ideally located to become the substrate of the next enzyme, so biochemical reactions can proceed rapidly
5. multi-enzyme complex orders the sequence of reactions

Question 25

how do r groups in the enzyme break substrates down?

Answer 25

1. the substrate is held in the active site by non-covalent bonds between the R groups of the binding a.a. and the substrate molecule
2. the R groups of the catalytic a.a. residues catalyse the conversion of the substrate to product
3. alteration in chemical conformation leads to product being released from the active site as it is no longer complementary to the active site

Question 26

compare the lock & key hypothesis and the induced fit hypothesis.

Answer 26

in the lock & key hypothesis, enzymes are viewed as rigid structures that only substrates that are exactly complementary can bind onto. (substrate specificity)
whereas in the induced fit hypothesis, the active site doesn’t have rigid conformation for only one substrate but rather is flexible, allowing more than one type of substrate to bind. upon the binding of the enzyme, the active site changes in conformation slightly to bind the substrate even more snugly so the active site is moulded into a specific conformation and it brought into close proximity with the substrate. one enzyme can catalyse reactions for a variety of substrates with similar chemical & physical properties (group specificity)

Question 27

how does optimum pH affect enzyme activity?

Answer 27

rate of reaction is maximum as intra-molecular bonds are intact and conformation of active site is ideal for binding, so frequency of effective collisions is the highest and the largest number of enzyme-substrate complexes are formed.