C1.1 Enzymes and Metabolism

Question 1

what are enzymes

Answer 1

bio catalysts made of proteins

Question 2

why are enzymes used as a way to control chemical reactions?

Answer 2

some are only produced under particular conditions, at certain stages or with particular substrates

Question 3

why are enzymes necessary

Answer 3

enable reactions to occur at high rates

Question 4

how is control over metabolism exerted

Answer 4

through enzymes

Question 5

what does anabolic refer to

Answer 5

larger molecules built up from smaller molecules through condensation reactions

Question 6

examples of anabolism

Answer 6

synthesis of proteins from amino acids
synthesis of polysaccharides from simple sugar
photosynthesis

Question 7

what is catabolism

Answer 7

the breakdown of larger molecules into smaller molecules, hydrolysis reactions

Question 8

examples of catabolism

Answer 8

hydrolysis of macromolecules into monomers in digestion
oxidation of substrates in respiration

Question 9

shape of enzymes

Answer 9

usually large, globular proteins, rounded

Question 10

properties of the active site of enzymes

Answer 10

binding to the substrate molecule
holding on to it while chemical reaction takes place
lowering the energy of the transition state

Question 11

what is the induced fit model

Answer 11

as the enzyme substrate complex forms, a slight change of shape is required in the enzyme and substrate.
this change raises the substrate to the transition state where it can react with

Question 12

what is the lock and key model

Answer 12

the active site is of complementary shape to the substrate and fits it perfectly
most enzymes seem to follow the model

Question 13

what are immobilised enzymes

Answer 13

enzymes that are embedded in membranes and are often more stable than free enzymes, providing a better environment for activity

Question 14

what are immobilised enzymes usually used for

Answer 14

food processions, pharmaceuticals or wastewater treatment

Question 15

advantages of immobilised enzymes

Answer 15

permits reuse of enzyme
product is enzyme free
enzyme may last longer

Question 16

what is denaturation

Answer 16

occurs when the weak intramolecular interactions within the globular protein break. This changes shape of the active site

Question 17

what happens to enzyme activity as temperature increases

Answer 17

increased kinetic energy leads to increases reactions and collisions

Question 18

optimum temperature in enzymes?

Answer 18

after the optimum point, enzyme activity decreases due to denaturation

Question 19

what happens when the pH value is not optimum for enzymes

Answer 19

a change in pH from the optimum value alters the bonding patterns, progressively changing the shape of the molecule, active site is inactive
effects are usually reversible

Question 20

what happens when substrate molecules are in excess of enzymes

Answer 20

a plateau of reactions is reached since all possible enzymes are already being used

Question 21

energy of the enzyme substrate complex

Answer 21

it exists at a local energy minimum and is quite stable

Question 22

transition state

Answer 22

the point where there is a maximum value of energy. Immediately the product is formed and energy released is

Question 23

activation energy

Answer 23

to bring about reaction, a small amount of energy is needed initially to break or weaken bonds in the substrate, forming the transition state. That is activation eergy

Question 24

how do enzymes work, in terms of energy

Answer 24

by lowering the amount of energy required to activate the reacting molecules by providing a new alternative reaction pathway

Question 25

extracellular enzymes

Answer 25

enzymes exported from cells, secreted by endocytosis to work externally

Question 26

intracellular enzymes

Answer 26

remain within cells and work there

Question 27

examples of intracellular enzyme catalysed reactions

Answer 27

glycolysis and the krebs cycle

Question 28

example of active energy

Answer 28

chemical potential to heat transfers it to active energy

Question 29

how much stored energy is available in a molecule

Answer 29

only part which is known as free energy and can be used for work

Question 30

exergonic reactions

Answer 30

reactions that release free energy. the products have less stored energy than the reactants
oxidation of glucose is example

Question 31

endergonic reactions

Answer 31

reactions in which energy is absorbed. Products have more stored energy than reactants
synthesis of proteins is example

Question 32

how are endergonic and exergonic reactions made possible

Answer 32

they are made possible in metabolism by both being coupled to each other through ATP

Question 33

what do molecules of ATP do in metabolism

Answer 33

they work as intermediates, linking energy absorbing and energy yielding reactions

Question 34

what type of metabolic pathway is glycolysis

Answer 34

linear

Question 35

what type of metabolic pathway is cyclical

Answer 35

krebs cycle

Question 36

what are enzyme inhibitors

Answer 36

they lower the rate of enzyme action

Question 37

competitive inhibitors

Answer 37

molecules that sufficiently resemble the substrate and compete for the active site

Question 38

non competitive inhibitors

Answer 38

they are unlike the substrate molecule but still combine with the enzyme. they attach close to the active site, party blocking access or changing its shape
adding excess substrates do not overcome its effects

Question 39

what are allosteric regulators

Answer 39

molecules that change the shape and activity of an enzyme by binding at an active site

Question 40

what are allosteric activators

Answer 40

temporarily stabilises the enzyme shape as an active and effective catalyst

Question 41

what are allosteric inhibitors

Answer 41

changes the shape to an inactive form

Question 42

what are statins

Answer 42

example of competitive inhibitors. partially block access to active ste
taken to reduce excess blood cholesterol and reduce risk of CHD

Question 43

End product inhibition

Answer 43

as the product molecule accumulates, the steps in the production process are switched off

Question 44

end product inhibition that converts threonine to isoleucine

Answer 44

isoleucine acts as a non competitive inhibitor by binding to allosteric site of enzyme threonine deaminase
inhibition of the enzyme turns off production of isoleucine
when isoleucine concentration is low, metabolic pathway can proceed as inhibition is low
as concentration increases, inhibition takes place and pathway regulated
when isoleucine concentration falls and enzyme acts in converting threonine to isoleucine

Question 45

mechanism based inhibition

Answer 45

when a molecule that has a similar substrate structure binds to the active site, molecule is then modified to produce a reactive group, which reacts irreversibly to form a stable inhibitor enzyme complex

Question 46

penicillin as mechanism based inhibition

Answer 46

it inhibits transpeptidase, causing bacterial cell walls to be weak. This can cause lysis of bacteria through osmosis
penicillin resembles part of the peptide chain of the way and transpeptidase binds to it instead