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Biology Module 2 > 2.4 Enzymes > Flashcards

2.4 Enzymes Flashcards

Enzymes

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1
Q

what is an enzyme

A

a biological catalyst which speeds up the rate of chemical reactions, without being used up itself

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2
Q

what is Vmax

A

where the rate of reaction is the highest, as all enzymes are saturated with substrates

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3
Q

what type of reactions do enzymes catalyse

A

metabolic reactions
- on cellular level (respiration)
- for organism as whole ( digestion)

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4
Q

what type of enzymes can you have

A

intracellular (inside cells)
extracellular (outside cells)

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5
Q

examples of intracellular enzymes

A
  • catalase works inside cells
    -catalyses the breakdown of hydrogen peroxide into O2 and H2O
  • H2O2 is a toxic by-product of many cellular reactions, and if built up can kill cells
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6
Q

examples of extracellular enzymes

A

AMYLASE=
- found in saliva, which is secreted into the mouth by salivary glands
- catalyses the hydrolysis of starch into maltose
TRYPSIN=
- produced by cells in the pancreas and secreted into the small intestine
- catalyses the hydrolysis of peptide bonds (turns big polypeptides into smaller polypeptides), to be later broken into amino acids by other enzymes

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7
Q

what type of protein are enzymes

A
  • globular
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8
Q

explain the enzyme active site

A
  • active site has a specific shape, which is determined by the enzymes tertiary structure
  • where the substrate binds to
  • for reaction to work, substrate has to fit the active sight (be complimentary), or reaction won’t be catalysed
  • this is why enzyme only works with very few substrates
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9
Q

what is activation energy

A
  • the amount of energy that needs to be supplied to chemicals before the reaction begins
  • often heat
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10
Q

how do enzymes speed up the rate of reaction

A
  • lower the activation energy needed, making the reaction happen at a lower temperature often
  • via forming an enzyme-substrate complex
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11
Q

what happens when an enzyme binds to a substrate

A
  • forms an enzyme-substrate complex
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12
Q

why do enzyme-substrate complexes lower activation energy

A

1) for JOINING molecules, anabolic reactions, attaching to the enzymes holds the substrate molecules close together, reducing any repulsion between molecules so they can bond more easily
2) for BREAKDOWN reaction, catabolic reactions, fitting into the active site puts a strain on the bonds in the substrate, meaning they break up more easily

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13
Q

what are the two models of enzyme action

A

lock and key
induced fit

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14
Q

what is the lock and key model

A
  • substrate fits PERFECTLY to the active site of the enzyme
  • enzyme is unchanged after reaction
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15
Q

what is the induced fit model

A
  • as the substrate binds, the active site changes shape slightly to fit the substrate more tightly
  • so substrates have to be MORE specific; must be right shape to fit enzyme but also make the active site change shape correctly too
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16
Q

what is the process of enzyme action

A
  • enzyme + substrate
  • enzyme-substrate complex
  • enzyme-product complex
  • enzyme + product
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17
Q

what are the 4 factors that affect enzyme activity

A

temperature
pH
enzyme concentration
substrate concentration

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18
Q

explain a graph for temperature affecting rate of enzyme activity

A
  • steady increase up to optimum
  • rapid decrease following
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19
Q

explain why and how temperature effects enzyme activity

A

INITIALLY:
- higher temperature means means more kinetic energy, so molecules move faster
- means more collisions, so more ESCs formed
- energy of collisions also increases, so each collision is more likely to result in a reaction
AFTERWARDS:
- rise in temperature means enzyme molecules vibrate more
- if too high, vibrations can break some bonds holding the enzyme in shape
- can change shape of active site so substrate molecules no longer fit
- enzyme denatured and no longer functions

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20
Q

what is the temperature coefficient

A

Q10
- shows how much the rate of reaction changes when the temp is raised by 10 degrees
- most reactions have value of around 2 (means rate doubles when temp is raised by 10 degrees)

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21
Q

how do you calculate the Q10 value

A

rate at higher temperature (x+10) / rate at lower temperature (x)

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22
Q

what is the optimum temperature in humans

A

37 degrees celsius
(closer to 60 for those used in washing up powders)

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23
Q

explain the graph of pH effect on enzyme activity

A
  • rapid increase
  • peak at optimum
  • rapid decrease
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24
Q

explain the pH graph

A
  • above and below the optimum
  • H+ ions in acids or OH- ions in alkalis can affect the charges of reactions
  • messing up the ionic and hydrogen bonds that hold the enzymes tertiary structure in place
  • changes the active site
  • denaturing enzyme
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25
Q

what is optimum pH in humans

A
  • most = pH 7 (neutral)
  • pepsin has optimum of 2 ( good as found in stomach which is acidic)
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26
Q

explain a graph of affects of enzyme concentration on rate of reaction

A
  • steady increase up and up
  • plateaus if substrate amount is limited
27
Q

explain effect of enzyme concentration of rate of reaction

A
  • the more enzyme molecules in a solution
  • the more likely a substrate collides and forms an ESC
  • increasing the rate of reaction
  • but if amount of substrate is limited
  • there is enough enzyme molecules to deal with all the substrate available
  • so adding more has no further effect
28
Q

explain the graph of substrate concentration on rate of reaction

A
  • steady increase up to a point
  • plateaus when has no longer effect
29
Q

explain the effects of substrate concentration on rate of reaction

A
  • more substrate molecules means collisions between enzyme and substrate is more likely, so more active sites used
  • more ESC’s so faster the rate
    HOWEVER:
  • reaches a point of saturation, where all the active sites are full
  • and adding more substrate will have no effect on the rate of reaction
  • as time goes on, substrate concentration decreases anyways unless more substrate added
  • so rate will decrease over time too (unless other factors change)
  • initial rate of reaction (close to 0 on graph) the highest rate
30
Q

what are the two ways of measuring the rate of an enzyme-controlled reaction

A
  • measure how fast the product is produced
  • measure how quickly the substrate disappears
31
Q

give example of where you can use the rate of substrate being used up PAG

A

the breakdown of starch into maltose using amylase:
1) put drops of iodine solution into spotting tile
2) put starch and amylase solution every minute into the discs
3) time when iodine no longer changes colour to blue or black (no starch)

32
Q

PAG: what are the variables in the catalase practical

A

INDEPENDENT: temperature (if factor)
DEPENDENT: the volume of oxygen produced
CONTROL: pH, enzyme concentration, substrate concentration, volume of both

33
Q

PAG : how do you investigate the effects of temperature on catalase activity

A

1) set up boiling tubes with equal volume and concentration of hydrogen peroxide
2) keep pH constant by adding equal volumes of buffer solution, set to the optimum pH of the enzyme
3) need to measure volume of oxygen produced, which can be done using a delivery tube and cylinder
4) put each boiling tube into a water bath set to a different temperature
5) put a test tube of catalase into each water bath too, and give 5 minutes for enzyme to reach set temperature
6) use a pipette to add a set volume of catalase into each boiling tube
7) record how much oxygen is produced in the first 60 seconds using a stopwatch
8) repeat at each temperature 3 times, and calculate mean of oxygen produced
9) calculate the mean rate of reaction by dividing the volume of oxygen produced by the time taken (cm cubed per second)
10) always carry out a control without catalase at each temperature

34
Q

what are cofactors (definition)

A

non-protein substances which are bound to enzymes to make them work (otherwise won’t)

35
Q

explain how cofactors work

A
  • inorganic molecules or ions
  • help the enzyme and substrate to bind together
  • don’t directly participate in the reaction
  • aren’t used up or changed in any way
36
Q

example of a cofactor

A
  • chloride ions Cl- are cofactors for the enzyme amylase
37
Q

what are coenzymes

A

cofactors which are organic molecules

38
Q

how do coenzymes work

A
  • participate in the reaction
  • and are changed by it
  • often act as carriers, moving chemical groups between different enzymes
  • continually recycled during this process
39
Q

example of a source of coenzymes

A

vitamins

40
Q

what is a prosthetic group

A

a cofactor which is tightly bound to the enzyme

41
Q

example of a prosthetic group

A

Zinc ions (Zn 2+)
- prosthetic group for carbonic anhydrase
- the ions are a permanent part of the enzymes active site
- (enzyme in red blood cell which catalyses the production of carbonic acid from water and carbon dioxide)

42
Q

what are enzyme inhibitors

A

molecules that bind to the enzyme that they inhibit, preventing its activity

43
Q

what are the two types of enzyme inhibitors (two groups too)

A

competitive and non-competitive
reversible and non-reversible

44
Q

how do competitive inhibitors work

A
  • molecules have similar shape to substrate molecules
  • they compete with the substrate molecules to bind to the active site , but no reaction takes place
  • by blocking the active site, no substrate molecule can fit in it
45
Q

explain the relationship between concentrations of competitive inhibitor and substrate

A
  • how much enzyme is inhibited depends on this
  • if high concentration of inhibitor, it’ll take up nearly all the active sites and hardly any of the substrate will get to the enzyme
  • if higher concentration of substrate, the substrates chance of getting to an active site before inhibitor will increase
  • increasing the rate of reaction up to a point
46
Q

explain graph of increasing substrate concentration and rate of reaction with competitive inhibitor

A
  • below rate without inhibitor, but eventually reaches same point
  • rate increases with substrate concentration
47
Q

how do non-competitive inhibitors work

A
  • molecules bind to the enzyme away from the active site
  • site they bind to is called the allosteric site
  • causes the enzymes active site to change shape so the substrate no longer binds to it
  • don’t compete with the substrate as they are different shapes
48
Q

explain how increasing the concentration of substrate will affect the rate of reaction with non-competitive inhibitors

A
  • won’t make a difference to the rate, as the enzyme activity will still be inhibited
  • on graph, it is well below and never reaches same amount
49
Q

what determines what type of inhibitor a molecule is

A
  • the bonds between the inhibitor and the enzyme
    1) if strong and covalent, the inhibitor cannot be removed easily and the inhibition is irreversible
    2) if weak hydrogen or ionic bonds, the inhibitor can be removed and the inhibition is reversible
50
Q

which medicinal drugs are enzyme inhibitors

A

antibiotics and antivirals

51
Q

how do antivirals work and give examples

A
  • drugs that stop viruses like HIV
  • e.g. reverse transcriptase inhibitors inhibit the enzyme reverse transcriptase (catalyses the replication of viral DNA)
  • prevents virus from replicating
52
Q

how do antibiotics work and give examples

A
  • penicillin inhibits transpeptidase, which catalyses the formations of proteins in bacterial cell wall
  • this weakens cell wall
  • prevents bacteria from regulating its osmotic pressure
  • cell bursts and bacterium is killed
53
Q

give examples of metabolic poisons as enzyme inhibitors

A

poisons which interfere with metabolic reactions (occur in cells) causing damage, illness or death
- cyanide
- malonate
- arsenic

54
Q

how does cyanide work

A
  • irreversible inhibitor of cytochrome c oxidase
  • enzyme which catalyses respiration
  • cells that can’t respire die
55
Q

how does malonate work

A
  • inhibits succinate dehydrogenase
  • which catalyses respiration reactions
56
Q

how does arsenic work

A
  • inhibits the action of pyruvate dehydrogenase
  • enzyme that catalyses respiration reactions
57
Q

what is a metabolic pathway

A

a series of connected metabolic reactions, where the product of one reaction takes part in the second reaction, and so on (each reaction is catalysed by a different enzyme)

58
Q

what is product inhibition

A

many enzymes are inhibited by the product of the reaction they catalyse

59
Q

what is end-product inhibition

A

-when the final product in a metabolic pathway inhibits an enzyme that acts earlier on in the pathway
-regulates the pathway and controls the amount of end product that gets made

60
Q

give an example of end-product inhibition

A
  • phosphofructokinase is an enzyme involved in the metabolic pathway that breaks down glucose to make ATP
  • ATP inhibits the action of phosphofructokinase
  • high levels of ATP prevent more ATP from being made
61
Q

what types of reactions are product and end-product inhibition, and what does this mean

A
  • reversible
  • means when the level of product starts to drop, the level of inhibition will also start to fall and the enzyme will begin to function again and make more product
62
Q

how to inactive precursors work

A
  • inactive precursors are enzyme which are produced in an inactive form
  • part of the precursor molecule inhibits the action of the enzyme
  • once this part is removed (e.g. by chemical reaction), the enzyme becomes active
  • changes the tertiary structure of the enzyme, particularly changing active site
63
Q

what is the point of inactive precursors and give example

A
  • to prevent them from causing damage to cells
  • some proteases (break down proteins) are synthesised as inactive precursors
    -stops them from damaging the proteins in the cell that they’re made in
64
Q

when finding optimum on graph, what must you remember

A

must be in between the 2 highest points, as we don’t actually know the optimum, cannot assume that we recorded it

Biology Module 2 (6 decks)

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