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CIE Biology A1 > enzymes > Flashcards

enzymes Flashcards

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1
Q

enzymes

A

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

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2
Q

active site

A

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

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3
Q

properties of catalysts

A

high molecular weight
temp sensitive
pH sensitive
specific

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4
Q

lock and key process

A
  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
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5
Q

induced fit model

A

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.

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6
Q

activation energy

A

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

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7
Q

methods enzymes use to lower the AE

A

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

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8
Q

factors affecting rate of enzyme-catalysed reactions

A

pH
substrate/enzyme concentration
inhibitors
activators

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9
Q

temp effect on enzyme catalysed reactions

A

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)

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10
Q

rate of increase in RoR for temp

A

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

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11
Q

pH effect on enzyme controlled RoR

A

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

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12
Q

substrate conc effect on RoR

A

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.

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13
Q

enzyme conc effect on RoR

A

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

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14
Q

how is RoR measured?

A

disappearance of a substrate

appearance of a product

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15
Q

what will occur as the reaction proceeds

A

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

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16
Q

enzyme inhuibitors

A

reduce rate of enzyme-catalysed reaction

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17
Q

types of enzyme inhibitors

A

non-reversible
reversible
competitive
non-competitive

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18
Q

competitive reversible inhibitors

A

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

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19
Q

example of competitive reversible inhibitor

A

ethanol

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

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20
Q

non-competitive reversible inhibitor

A

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.

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21
Q

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

A

no effect

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22
Q

effect on inhibitors when substrate conc is decreased

A

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

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23
Q

effect on inhibitors when substrate concentration is increased

A

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

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24
Q

metabolic pathways

A

series of chemical reactions, each catalysed by a different enzyme

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25
Q

end product inhibition

A

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

26
Q

why is end-product inhibition useful?

A

would be wasteful to produce a product in excess

27
Q

Michaeles-Menten constant

A

measure of the affinity of an enzyme for its substrate

higher affinity» lower Km and faster RoR

28
Q

Vmax

A

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

29
Q

formula for Km

A

Vmax/2 = substrate concentration

30
Q

immobilisation of enzymes

A

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

31
Q

purpose of enzyme immobilisation

A

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

32
Q

process of enzyme immobilisation

A

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.

33
Q

example of enzyme immobilisation

A

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

34
Q

positives of immobilisation

A 
thermostable and pH stable
can be removed at a set time
reusable
don't contaminate
substrate can continuously be added into reaction
35
Q

negatives of immobilisation

A

less active
enzyme alteration can affect specificity
more expensive

36
Q

methods of immobilisation

A

adsorption
membrane separation
covalent bonding

37
Q

adsorption

A

enzyme is physically attached to a support via weak binding forces

38
Q

covalent bonding immobilisation

A

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

39
Q

membrane separation

A

enzyme is separated from a substrate via a partially permeable membrane

40
Q

hydrolases

A

enzymes catalysing hydrolysis reactions

41
Q

maltose

A

disaccharide consisting of 2 alpha glucose molecules joined by glycosidic bond

42
Q

maltase

A

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

43
Q

transferases

A

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

44
Q

example of transferase

A

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

45
Q

oxireductase

A

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

46
Q

krebbs cycle

A

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

47
Q

active site

A

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

48
Q

what must happen for a reaction to occur

A

reactants must collide with sufficient speed at the correct orientation

49
Q

intracellular enzyme

A

enzyme performing function within the cell that produces it

50
Q

extracellular enzyme

A

an enzyme that functions outside the cell from which it originates

51
Q

why are digestion enzymes mostly extracellular?

A

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

52
Q

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

A

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

53
Q

catabolic reactions

A

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

54
Q

examples of catabolic reactions

A

hydrolysis/cellular respiration

55
Q

exergonic

A

net release of energy

56
Q

anabolic reactions

A

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

57
Q

examples of anabolic reactions

A

protein synthesis and photosynthesis

58
Q

endergonic

A

involving a net use of energy

59
Q

how do enzymes lower the Ea of a reaction

A

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

60
Q

basis of lock and key model

A

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.

61
Q

immobilised enzyme

A

an enzyme bound to a stationary support

CIE Biology A1 (15 decks)

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