enzymes

Question 1

enzymes

Answer 1

globular proteins acting as biological catalysts so that reactions in metabolising organisms may work at a suitable pace.

Question 2

active site

Answer 2

where the specific substrate binds, created by the precise folding of the enzyme’s amino acid chain.

Question 3

properties of catalysts

Answer 3

high molecular weight
temp sensitive
pH sensitive
specific

Question 4

lock and key process

Answer 4

1. enzyme binds to substrate, forming enzyme-substrate complex > active site doesn’t change shape
2. reaction occurs, forming an enzyme-product complex
3. products diffuse away from active site

Question 5

induced fit model

Answer 5

substrate binds to the enzyme at the active site, inducing the enzyme to change shape to fit exactly.
proteins have a 3 dimensional flexibility. weak chemical bonds form which strain bonds in the substrate to lower the energy required to reach transition state, leading to an intermediate ES complex. reactions happen after substrate fit has occurred.

Question 6

activation energy

Answer 6

amount of energy given to a reaction in order for it to proceed.

Question 7

methods enzymes use to lower the AE

Answer 7

hold substrates at correct angle for collision
donation/acceptance of protons
allowing initial breaking of bonds within the substrate to happen more easily by destabilising bonds within the substrate

Question 8

factors affecting rate of enzyme-catalysed reactions

Answer 8

pH
substrate/enzyme concentration
inhibitors
activators

Question 9

temp effect on enzyme catalysed reactions

Answer 9

increases speed of motion and therefore no. of collisions
at higher temps, more enzyme-substrate complexes are formed and more product molecules are found at higher temps as molecular motion and collisions increase
past optimum temp, bonds stabilising the enzyme’s tertiary structure are broken and the enzyme changes shape so can’t bind to substrate (denatured)

Question 10

rate of increase in RoR for temp

Answer 10

between 4 and 40 degrees RoR doubles for every 10 degree rise in temp until an optimum temp is reached
Q10=2

Question 11

pH effect on enzyme controlled RoR

Answer 11

changes ionic and hydrogen bonding, holding the tertiary shape of enzymes , extremes of pH can then break these bonds and denature the enzyme

Question 12

substrate conc effect on RoR

Answer 12

increases as substrate concentration increases and reaches a maximum, past which has no effect on RoR as all active sites are full, therefore enzyme conc is the limiting factor.

Question 13

enzyme conc effect on RoR

Answer 13

RoR is proportional to enzyme concentration (usually lower than substrate conc which is rarely a limiting factor.

Question 14

how is RoR measured?

Answer 14

disappearance of a substrate

appearance of a product

Question 15

what will occur as the reaction proceeds

Answer 15

fewer collisions, fewer enzyme complexes formed, less product formation, RoR slows and eventually stops when all the substrate has converted into product

Question 16

enzyme inhuibitors

Answer 16

reduce rate of enzyme-catalysed reaction

Question 17

types of enzyme inhibitors

Answer 17

non-reversible
reversible
competitive
non-competitive

Question 18

competitive reversible inhibitors

Answer 18

decrease RoR via reversible combination with enzyme
similar shape to normal substrate, competing for active site, forming enzyme-inhibitor complex, preventing ES complex forming
more inhibitor present in relation to substrate, greater degree of inhibition

Question 19

example of competitive reversible inhibitor

Answer 19

ethanol

slows oxalic acid production from ethylene glycol in body so kidney is damaged

Question 20

non-competitive reversible inhibitor

Answer 20

binds to enzyme at allosteric site, disrupting hydrogen bonds and hydrophobic interactions in the tertiary structure of the enzyme, causing the enzyme to change shape, including active site so that no ES complex can be formed.

Question 21

substrate conc effect on degree of inhibition w non-competitive reversible inhibitors

Answer 21

no effect

Question 22

effect on inhibitors when substrate conc is decreased

Answer 22

competitive inhibitors compete for active site and fewer substrate molecules are converted into product, decreasing RoR
non-competitive reduce RoR

Question 23

effect on inhibitors when substrate concentration is increased

Answer 23

effect of competitive inhibitor is overcome and max RoR is reached
non-competitive effect isn’t overcome as all bound enzymes don’t convert into products

Question 24

metabolic pathways

Answer 24

series of chemical reactions, each catalysed by a different enzyme

Question 25

end product inhibition

Answer 25

a system used to control metabolic pathways end product acts as non-competitive reversible inhibitor to the first enzyme, preventing further produvt from being formed until product is used up

Question 26

why is end-product inhibition useful?

Answer 26

would be wasteful to produce a product in excess

Question 27

Michaeles-Menten constant

Answer 27

measure of the affinity of an enzyme for its substrate | higher affinity>> lower Km and faster RoR

Question 28

Vmax

Answer 28

max rate of reaction possible for a particular enzyme, assuming unlimited substrate

Question 29

formula for Km

Answer 29

Vmax/2 = substrate concentration

Question 30

immobilisation of enzymes

Answer 30

converting enzymes into their insoluble form via binding with an insoluble polymer

Question 31

purpose of enzyme immobilisation

Answer 31

enables reuse of enzymes and prevents contamination rather than difficulty in extraction of enzyme once placed in solution

Question 32

process of enzyme immobilisation

Answer 32

mixture w an inert gel (eg. alginate) and addition of calcium chloride forms small beads containing the enzyme. substrate can then diffuse into the bead, forming an ES complex and then product.

Question 33

example of enzyme immobilisation

Answer 33

immobilised lactase in order to convert lactose in milk into galactose and glucose

Question 34

positives of immobilisation

Answer 34

``` thermostable and pH stable can be removed at a set time reusable don't contaminate substrate can continuously be added into reaction ```

Question 35

negatives of immobilisation

Answer 35

less active enzyme alteration can affect specificity more expensive

Question 36

methods of immobilisation

Answer 36

adsorption membrane separation covalent bonding

Question 37

adsorption

Answer 37

enzyme is physically attached to a support via weak binding forces

Question 38

covalent bonding immobilisation

Answer 38

enzyme bound to an inert substance via covalent bonds and enzymes may also be bound by cross-linking agents

Question 39

membrane separation

Answer 39

enzyme is separated from a substrate via a partially permeable membrane

Question 40

hydrolases

Answer 40

enzymes catalysing hydrolysis reactions

Question 41

maltose

Answer 41

disaccharide consisting of 2 alpha glucose molecules joined by glycosidic bond

Question 42

maltase

Answer 42

a hydrolase enzyme that catalyses hydrolysis of maltose into 2 glucose molecules

Question 43

transferases

Answer 43

enzymes that catalyse reactions involving the transfer of atoms or groups of atoms from one molecule to the other

Question 44

example of transferase

Answer 44

during respiration, a phosphate group is transferred from ATP to a glucose molecule, activating the glucose

Question 45

oxireductase

Answer 45

enzymes that catalyse reactions involving oxidation and reduction have a role in the biochemistry of respiration

Question 46

krebbs cycle

Answer 46

the stepwise oxidation of a 6 carbon acid into a 4 carbon acid in which hydrogen atoms are removed in pairs dehydrogenase is a type of oxireductase speeding up this reaction

Question 47

active site

Answer 47

where specific substrates bind, shape and chemistry is specific and a function of the polypeptide, complex tertiary structure

Question 48

what must happen for a reaction to occur

Answer 48

reactants must collide with sufficient speed at the correct orientation

Question 49

intracellular enzyme

Answer 49

enzyme performing function within the cell that produces it

Question 50

extracellular enzyme

Answer 50

an enzyme that functions outside the cell from which it originates

Question 51

why are digestion enzymes mostly extracellular?

Answer 51

must be broken down outside before they can enter cells directly as are too big.

Question 52

why would an extracellular enzyme be produced in an inactive form?

Answer 52

so that it doesn't damage other proteins while in its active form

Question 53

catabolic reactions

Answer 53

chemical bonds broken within a substrate molecule, causing it to break apart to become two separate molecules exergonic

Question 54

examples of catabolic reactions

Answer 54

hydrolysis/cellular respiration

Question 55

exergonic

Answer 55

net release of energy

Question 56

anabolic reactions

Answer 56

chemical bond formation, causing two substrate molecules to form a single molecule endergonic

Question 57

examples of anabolic reactions

Answer 57

protein synthesis and photosynthesis

Question 58

endergonic

Answer 58

involving a net use of energy

Question 59

how do enzymes lower the Ea of a reaction

Answer 59

influence bond stability in reactants, creating an unstable transition state in the substrate so is more reactive.

Question 60

basis of lock and key model

Answer 60

enzymes are rigid structures and the active site was perfectly matching to the substrate or the reaction wouldn't proceed. supported by early x ray crystallography studies, since modified to recognise the flexibility of enzymes.

Question 61

immobilised enzyme

Answer 61

an enzyme bound to a stationary support