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Biology > Enzymes > Flashcards

Enzymes Flashcards

1
Q

What is an enzyme?

A

A protein molecule that acts as a biological catalyst

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2
Q

what type of protein is an enzyme and how does it help?

A

globular protein so hydrophillic amino acids on outside and hydrophobic on inside - makes it soluble in water

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3
Q

anabolic reaction

A

builds up molecuels

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4
Q

catabolic reactions

A

break down molecules

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5
Q

metabolism

A

combination of anabolic and catabolic reactions - all different reactions happening in a cell

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6
Q

metabolic pathway

A

sequence of enzyme controlled reactions

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7
Q

extracellular

A

enzymes that catalyse reactions outside of cells eg. breaking down nutrient molecules for digestion

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8
Q

intracellular

A

enzymes that catalyse reactions inside cells eg. synthesising polymers from monomers like making polysaccharides

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9
Q

example of intracellular enzymes and what it breaks down

A
  • catalase - hydrogen peroxide to water and oxygen
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10
Q

examples of extracellular enzymes and what they break down

A
  • Amylase - starch into maltose
  • Trypsin - protein into peptides
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11
Q

structure of an enzyme’s active site

A

amino acids interact with each other to maintain a specific tertiary structure - means it has a specific active site to catalyse specific reactions

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12
Q

induced-fit hypothesis

A
  • the tertiary structure of the active site is flexible and changes shape slightly as the substrate enters
  • the bonds formed between substrate and enzyme help catalyse the reaction, lowering activation energy
  • when the product leaves the enzyme the active site returns to its inactive state
  • other substrate molecules cannot form the correct bonds with the active site so the tertiary structure doesn’t change shape and fit
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13
Q

lock and key hypothesis

A
  • a specific substrate forms temporary bonds with amino acids on the surface of the active site forming enzyme-substrate complex and helping lower activation energy
  • substrate reacts and products formed in an enzyme-product complex
  • product released
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14
Q

what can the quaternary structure of an enzyme mean?

A
  • they can have more than one active site
  • eg. catalase has 4 identical polypeptide chains and therefore 4 active sites
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15
Q

activation energy

A

amount of energy that must be applied for the reaction to proceed

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16
Q

how do enzymes affect activation energy?

A

they lower it by acting as catalysts and forming enzyme-substrate complexes

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17
Q

characteristics of enzymes

A
  • change only the rate of reaction, not end products
  • specific to one reaction
  • globular proteins
  • activity affected by temp. and pH
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18
Q

Digestion of starch

A
  • starch polymers broken down into maltose by amylase (produced by salivary glands and pancreas)
  • Maltose broken down into glucose by maltase (produced by small intestine)
  • glucose is then small enough to be absorbed by cells lining the digestive system
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19
Q

Digestion of proteins and where is enzyme produced?

A
  • Trypsin is a protease that catalyses digestion of proteins into smaller peptides
  • then broken down further into amino acids by other proteases and absorbed by cells lining the digestive system
  • Trypsin - produced in pancreas and released into small intestine
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20
Q

Effect of low temp on enzyme activity

A

low rate of reaction
- low kinetic energy so move slowly
- few successful collisions between enzyme and substrate

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21
Q

effect of optimum temp on enzyme activity

A

high rate of reaction
- lots of kinetic energy so move quickly
- lots of successful collisions between enzyme and substrate

22
Q

Effect of very high temp on enzyme activity

A

low rate of reaction
- heat causes loads of kinetic energy and enzymes vibrate very fast - breaks the hydrogen bonds maintaining tertiary structure of enzyme
- active site changes and substrate doesn’t fit
- enzyme denatures
- no successful collisions

23
Q

what is temperature coefficient (Q10)?

A
  • measure rate of reaction at certain temp (eg. 20 degrees)
  • measure rate at 10 degrees higher (30 degrees)
  • temperature coefficient = higher (30)/lower (20)
24
Q

what does a graph measuring effect of temp on rate of reaction look like?

A

starts flatter, curves up u-shaped, then rapidly falls down

25
Q

effect of NOT optimum pH ( too high/low conc. hydrogen ions) on enzyme activity

A

low rate of reaction
- hydrogen ions can bond with R groups on amino acids of protein (including on active site)
- Hydrogen ions bonding to active site can prevent R groups bonding to substrate, by breaking tertiary structure
- substrate can’t bond with active site
- no successful collisions

26
Q

graph showing effect of pH on enzyme activity

A

bell shaped, with highest point changing depending on optimum pH

27
Q

What effect does low substrate conc have on enzyme activity?

A

low rate
- few substrate molecules limits chances of successful collisions

28
Q

what effect does high substrate conc have on enzyme activity?

A

high rate
- more substrate molecules increases chances of successful collisions

29
Q

what does graph showing effect of substrate conc look like?

A
  • substrate conc is directly proportional to rate of reaction at first so straight diagonal line through 0
  • then reaches Vmax where every enzyme is occupied so graph goes horizontal
30
Q

What is Vmax?

A

the maximum rate of reaction
- occurs when all the active sites are occupied by substrates, no more enzyme-substrate complexes can be made until products are released
- enzymes are saturated
- occurs when increasing substrate conc.

31
Q

effect of low enzyme conc on rate of reaction

A

low rate
- low chance of successful collisions between enzyme and substrate

32
Q

what does graph showing effect of enzyme conc look like?

A
  • enzyme conc is directly proportional to rate of reaction at first so straight diagonal line through 0
  • then line goes horizontal if substrate conc is not increased becuase there aren’t enough substrates to bind with enzymes
33
Q

How do you make different concentrations of catalase?

A

Serial dilution
- add 1ml of stock solution to 9ml distilled water
- add 1ml of that solution to 9ml of distilled water
- repeat a number of times to get serial dilution

34
Q

method of investigating effect of substrate conc on enzyme activity

A
  • Put 100cm^3 hydrogen peroxide and one potato cylinder into conical flask
  • set up conical flask with bung going into upside-down test tube in trough full of water
  • record volume of gas given off every 30s for 3 min
  • Repeat for other concentrations using 100cm^3 each time
  • calculate mean, standard deviation and rate of gas production
35
Q

How do competitive inhibitors work?

A
  • a molecule a similar shape as a substrate fits into the active site
  • This blocks the substrate from entering the active site, preventing the enzyme catalysing the reaction
  • slows the rate of reaction
  • eg. malonate is inhibitor competing with succinate and can inhibit respiration
36
Q

examples of competitive inhibitors

A
  • malonate is inhibitor competing with succinate and can inhibit respiration
  • methotrexate - used to treat cancers (reversible)
  • penicillin - used to treat bacterial infections (irreversible)
37
Q

how do you reduce the effect of a competitive inhibitor?

A

increase substrate conc. - makes it much -more likely enzyme will collide with substrate rather than inhibitor

38
Q

how does a graph increasing substrate conc. change when adding a fixed conc. of a competitive inhibitor?

A
  • will go from straight diagonal line, then reaching Vmax and going horizontal to one straight diagonal line reaching the same end point but not going horizontal
39
Q

what effect do competitive inhibitors have on rate of reaction?

A
  • they slow it down
  • much more effective initially but as substrate conc. increases they become less effective
40
Q

How do non-competitive inhibitors work?

A
  • inhibitor binds to enzyme at the allosteric site
  • causes tertiary structure of enzyme to change - active site changes
  • active site no longer has complementary shape for substrate to bind to
  • cannot form enzyme-substrate complexes lowering rate of reaction
  • eg. cyanide
41
Q

why does increasing the substrate conc not reduce the effect of non-competitive inhibitors?

A

it causes the shape of the active site to change so even when more substrate is being added there is no active sites for it to bind to

42
Q

how does a graph increasing substrate conc. change when adding a fixed conc. of a NON-competitive inhibitor?

A

It is parallel to it but lower down (r-shaped) as increasing substrate conc doesn’t effect it

43
Q

what is end product inhibition?

A

the final product in a metabolic pathway inhibits an early stage enzyme in the pathway
- used to reduce rate of metabolic pathway if less product is needed
- example of negative feedback - keeps level of molecules in a set range
- example of non-competitive inhibition

44
Q

examples of end product inhibition

A
  • eg. in protein synthesis if level of amino acids get too high they will inhibit the first enzyme in the pathway that makes them
  • eg. in respiration if ATP levels get too high they inhibit the first enzyme in the pathway that makes them
45
Q

reversible inhibitors

A
  • bind temporarily to enzyme
  • form weak H/ionic bonds with enzyme
  • effects reversed by change in environment for enzyme
46
Q

non-reversible inhibitors

A
  • binds permanently with enzyme
  • strong covalent bonds with enzyme
  • cell must produce more of the enzyme by activating gene so the enzymes are transcribed and translated
47
Q

Difference between cofactor and coenzyme

A

cofactor - a non-protein inorganic molecule that is required by an enzyme to function eg. amylase requires chloride ion
coenzyme - an organic molecule required by an enzyme to function eg. vitamin B3 used to move H atoms between molecules in respiration
- help transfer atoms or groups from one reaction to another or may form a part of the active site

48
Q

When can a co-factor be a prosthetic group?

A
  • when it’s tightly bound and forms
    a permanent feature of the enzyme
    eg. zinc ion is prosthetic group for carbonic anhydrase to metabolise CO2
49
Q

why is precursor activation needed?

A
  • many enzymes produced in the inactive form - inactive precursor enzymes
  • happens if enzyme can cause damage to cells producing them or tissues where they’re released
  • precursor enzymes need to undergo a change in shape (tertiary structure) of the active site to be activated
50
Q

What is the process of precursor activation?

A
  • before co-factor added enzyme is called an apoenzyme
  • when co-factor added and enzyme is activated - holoenzyme
  • change in tertiary structure can also be brought about by the action of another enzyme
  • sometimes the change in tertiary structure is brought about by change in environment not co-factor - these are called zymogens or proenzymes
51
Q

how do you measure rate of reaction from a graph showing amount of product in a certain time?

A
  • draw a tangent on the r-shaped curve touching the time we’re interested in
  • then calculate the gradient by making it into a triangle and measure vertical side (y) and horizontal side (x)
  • y/x
52
Q

how would you describe the r-shaped graph showing the amount of product made in a certain time with a fixed substrate conc?
(initial, middle, end)

A
  • rapid initial rate - lots of substrate molecules so high frequency of successful collisions
  • slower rate - some of the substrate has been turned into product so chance of substrate colliding with active site decreases
  • reaction stops - all substrate molecules converted into product so no chance of successful collision

Biology (21 decks)

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