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OCR A Level Biology A > 2.1.4 Enzymes > Flashcards

2.1.4 Enzymes Flashcards

1
Q

why are enzymes called biological catalysts

A

because they speed up metabolic reactions in living organisms

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2
Q

what type of proteins are enzymes

A

globular proteins with a tertiary structure

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3
Q

what is enzyme’s activity affected by

A
  • pH
  • temperature
  • concentration of enzymes + susbtrate
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4
Q

what can enzymes affect by regulating metabolic reactions at a cellular and whole organism level

A
  • structure
  • function
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5
Q

what does it mean if an enzyme catalyses intracellular reactions

A
  • they act within cells
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6
Q

give an example of an intracellular enzyme

A
  • catalase works insides cells to catalyse the breakdown of hydrogen peroxide to harmless O2 and H2O
  • hydrogen peroxide is a toxic and if accumulated it can kill cells
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7
Q

what does it mean if an enzyme catalyses extracellular reactions

A
  • they work outside the cells
  • they’re often secreted from the cells where they’re made and act on their substrates extracellularly
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8
Q

give examples of extracellular enzymes

A
  • digestive enzymes: they digest large molecules and the products of digestion are absorbed into bloodstream
  • amylase is found in saliva secreted by salivary glands and catalyses the hydrolysis of starch into maltose in the mouth
  • trypsin catalyses the hydrolysis of peptide bonds to turn polypeptides into smaller ones (and eventually amino acids)
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9
Q

describe the structure of enzymes

A
  • globular proteins which has an active site with a specific shape where a complimentary substrate binds to
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10
Q

what determines an enzymes active site shape

A

the enzyme’s tertiary structure

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11
Q

what does the lock and key hypothesis propose

A
  • when substrate binds to active site an enzyme-substrate complex is formed
  • substrate reacts and products are formed in an enzyme-product complex
  • products are released + enzyme is unchanged and can take part in subsequent reactions
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12
Q

what does the induced fit hypothesis propose

A
  • when the substrate fits in the active site, the active site changes shape slightly to mould itself around the substrate
  • when an enzyme-substrate complex is formed, it weakens the bonds holding it together
  • this lowers activation energy needed to break the bonds for the reaction to proceed
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13
Q

how do enzymes lower the activation energy of a reaction

A
  • chemical reactions need energy to activate
  • chemicals can be heated to inc kinetic energy and collisions therefore
    > however in living cells temp can’t be raised by a lot as proteins would denature
  • as enzymes have complimentary active site to substrate they can speed up reaction by helping molecules to collide successfully and reduce activation energy
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14
Q

what is effect of increasing temp on enzyme’s rate of reaction

A
  • as temp increases there’s higher frequency of successful collisions when substrate enters active site
  • more enzyme-substrate complex are formed
  • so more enzyme-product complex are formed
  • more product released from active site
  • faster rate of reaction
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15
Q

what is effect on rate of reaction at optimum temp

A
  • maximum number of successful collisions
  • maximum ESC
  • maximum EPC
  • maximum product released
  • maximum rate of reaction
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16
Q

what happens to rate of reactions as the temp goes above optimum temp

A
  • enzymes denature as it loses tertiary structure due to high heat causing molecules to vibrate and move around more
    > this strains the bonds and eventually breaks them (weak hydrogen bonds + ionic interactions break)
  • active site no longer specific + complimentary to substrate
  • less ESC
  • less EPC
  • less product released
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17
Q

what is optimum temperature

A
  • the temperature at which the enzyme works best
    > it’s at which the enzyme has its maximum rate of reaction
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18
Q

what is the temperature coefficient, Q10

A
  • Q10 = RT / RT - 10
  • its a measure of the rate of change as a result of increasing the temp by 10C
    > so if the Q10 is 2, it means for every 10C rise in temp the rate of reaction is doubled
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19
Q

what is pH

A
  • a measure of the H+ ion concentration
  • the higher the H+ concentration, the lower the pH (acidic)
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20
Q

what impact does pH have on enzymes

A
  • the H+ ions can disrupt the bonding in enzymes
  • as they interact with charged R-groups present on amino acids so the R-groups can’t interact with each other + leads to bond breaking
    > hydrogen bonds + ionic interactions between amino acid R-groups hold proteins in their 3D shape
    > ionic interactions and hydrogen bonds will be affected the most
  • this then changes shape of the active site + so rate of reaction is decreased
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21
Q

what happens to the rate of reaction as pH is altered slightly above/below optimum

A
  • ionic bonding is disrupted as less or more H+ ions are present so tertiary protein structure is changed
  • active site changing shape slightly means substrate doesn’t fit properly so less ESC + less EPC + less products
  • mild pH change effects are reversible
22
Q

what happens to the rate of reaction as there is an excess/deficiency of H+ ions

A
  • severe disruption of ionic bonds of enzymes
    > enzyme denatures as active site is lost so the substrate can no longer bind
  • no ESC + EPC + so no products formed
23
Q

what is the effect of substrate concentration on rate of enzyme-catalysed reactions

A
  • as substrate conc increases so does the rate of reaction
  • there is a higher ratio of substrate to enzyme molecules so there will be more frequent collisions with the active site leading to successful collisions as more ESC are formed
24
Q

what does it mean if the rate of reaction of an increasing substrate conc reaches V-max

A
  • all active sited are occupied
  • reaction can’t continue as enzymes are the limiting factor
    > adding more substrate means they can’t successfully collide + fit into active site
25
Q

what is the effect of enzyme concentration on rate of enzyme-catalysed reactions

A
  • as enzyme conc increases so does the rate of reaction
  • more active sites available so more successful collisions between enzyme and substrate forming more ESC
  • if the enzyme conc increases further there will be no increase in rate of reaction because substrate will be limiting factor as there aren’t enough to occupy the extra active sites
  • unless the substrate concentration is not increased, the rate of reaction stays the same
26
Q

how would you maintain and monitor the temperature in a PAG

A
  • maintain = thermostatically electric water bath
  • monitor = thermometer
27
Q

how would you maintain and monitor the pH in a PAG

A
  • maintain = pH buffers
  • monitor = pH probe
28
Q

what is an independent variable

A
  • the variable that you change
    > e.g. conc of a solution or temp etc
29
Q

what is a dependent variable

A
  • the variable you measure to see how the independent variable has affected it
30
Q

define cofactors

A
  • cofactors are small non-protein molecules that help enzymes to carry out their function
    > some enzymes can only work if a cofactor is attached to it
31
Q

what are inorganic cofactors

A
  • they help by binding the enzyme and substrate together
  • don’t directly participate in the reaction so aren’t used up / changed
32
Q

where are inorganic cofactors obtained from

A
  • obtained via diet as minerals, including iron, calcium, chloride and zinc ions
33
Q

what is an example of an inorganic cofactor

A
  • the enzyme amylase has the cofactor chloride ions that help form the shape of the active site
34
Q

what are coenzymes

A
  • organic cofactors that participate in the reaction + and are changed
  • often act as carriers by making chemical groups between diff enzymes
  • coenzymes need to be recycles to their original state, sometimes by a diff enzyme
35
Q

where are coenzymes derived from

A
  • derived from vitamins (organic molecules found in the diet)
36
Q

what is an example of a coenzyme

A
  • coenzyme NAD is derived from vitamin B3
37
Q

what are prosthetic groups

A
  • they’re cofactors that are tightly bound, by covalent bonds, to the enzyme and form a permanent feature of the protein
38
Q

what is an example of a prosthetic group

A
  • zinc ions form important part of structure of carbonic anhydrase
    > enzyme necessary for metabolism of CO2
39
Q

how are cofactors bound to enzymes

A
  • some are loosely or temporarily bound to enzyme protein in order to activate them
  • others like prosthetic groups are permanently bound to them
40
Q

what are inhibitors

A
  • molecules that prevent the enzyme from carrying out their normal function of catalysis
    > they bind to enzyme and can influence how a substrate binds to enzyme or effects enzyme’s turnover number
    > some block or change shape of active site
41
Q

what are competitive inhibitors

A
  • molecule with a similar shape to substrate + so competes with substrate to bind with the active site, blocking the substrate from entering it
    > prevent enzyme from catalysing the reaction
42
Q

what does the degree of inhibition depend on in competitive inhibition

A
  • conc of substrate and inhibitor molecules + enzymes
  • if there’s higher conc of competitive inhibitors they will collide more often with active site and reduce free enzyme active sites for substrate molecules to bind with
  • inc substrate con ‘dilutes’ / weakens effect of inhibitors as more substrate are likely to collide + bind withe active site
43
Q

what effect does competitive inhibitors have on rate of reaction

A
  • reduces rate of formation of ESC + EPC and therefore product form formation
    > lower rate of reaction
  • however V-max not change because if substrate conc increased enough, that there is more substrate than inhibitor, the original Vmax can still be achieved
44
Q

are enzyme inhibition by competitive inhibitors reversible or not

A
  • most competitive inhibitors only bind temporarily so effect is reversible
  • increasing substrate conc can reduce effect of reversible competitive inhibition
  • however some such as aspirin are irreversible
45
Q

what is an inactivator

A
  • if competitive inhibitor binds irreversibly to the enzyme’s active sit it’s called an inactivator
46
Q

what are non competitive inhibitors

A
  • inhibitors that bind to the enzyme at the allosteric site (location other than the active site)
    > causes tertiary structure to change + so active site changes shape
  • active site no longer complimentary to substrate so can’t bind
    > no ESC + EPC + products formed
47
Q

what is the effect of non competitive inhibitors on rate of reaction

A
  • inc substrate con has no effect as active sites are altered
  • inc inhibitors will decrease rate of reaction further as more active sites become unavailable
48
Q

what is end product inhibition

A
  • term used for enzyme inhibition that occurs when the products of a reaction acts as an inhibitor to the enzyme that produce it
    > serves as negative feedback
  • works by product tightly binding to enzyme so it can’t form more of the product than the cell needs
49
Q

what can enzyme inhibitors be used for

A
  • used by organisms to control metabolic reactions
    > allows products to be produced in specific amounts
50
Q

can irreversible inhibitors be removed

A
  • no, they remain attached to the enzyme

OCR A Level Biology A (6 decks)

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