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A level- Biology > Enzymes > Flashcards

Enzymes Flashcards

1
Q

Define the term enzymes

A

Enzymes are biological catalysts that interact with substrate molecules to facilitate chemical reactions. Usually globular proteins.

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2
Q

Define the term substrate

A

A substance used or acted on, by another process or substance. For example a reactant in an enzyme-catalysed reaction.

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3
Q

Define the term product

A

The result of a chemical reaction.

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4
Q

Explain why enzymes are necessary to life.

A

Most processes necessary to life involve chemical reactions which need to happen very fast -so are catalysed by an enzyme.

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5
Q

Define the term anabolic reactions

A

Anabolism refers to chemical reactions in which simpler substances are combined to form more complex molecules.
Anabolic reactions build new molecules and or store energy. And they normally require energy.

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6
Q

Define the term catabolic reactions

A

Catabolism refers to chemical reactions that result in the breakdown of more complex organic molecules into simpler substances.
Catabolic reactions usually release energy that is used to drive chemical reactions i.e. anabolic reactions.

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7
Q

Define the term metabolism

A

Metabolism is a term that is used to describe all chemical reactions involved in maintaining the living state of the cells and the organism. All reactions that occur in the body.

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8
Q

Explain how enzymes can affect both the structure and function of cells and whole organisms.

A

Enzymes can affect the structures in and organism e.g. enzymes are involves in the production of collagen and other proteins. These can affect the structures of cells and organisms.
Enzymes are specific so carry out a specific function, so can change the function of cells.

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9
Q

Define the term intracellular enzymes

A

Enzymes inside cells

Catalase

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10
Q

Define the term extracellular enzymes

A

Enzymes outside cells

Amylase and trypsin

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11
Q

State the substrates and products for the enzymes catalase

A

Catalyses the breakdown of hydrogen peroxide to oxygen and water.
Hydrogen peroxide is a toxic by-product of several cellular reactions- can kill cells if builds up.

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12
Q

State the substrates and products for the enzymes amylase.

A

Catalyses the hydrolysis of starch into maltose in the mouth.
Maltose is broken down to glucose by maltase which is in the small intestine.
It is found in saliva and secreted into the mouth by the salivary glands.

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13
Q

State the substrates and products for the enzymes trypsin.

A

Catalyses the hydrolyses of peptide bonds turning big polypeptides into smaller ones.
Produced in the pancreas and secreted into the small intestine.

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14
Q

Explain the role of extracellular enzymes in general..

A

They breakdown large nutrient molecules into smaller molecules by the process of digestion.

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15
Q

Define the terms “active site”

A

The area of an enzyme with a shape complementary to a specific substrate, allowing the enzyme to bind to a substrate with specificity

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16
Q

Define the terms complementary shape.

A

The shape of the active sites of enzymes are exactly complementary to the shape of the substrate.
Lock and Key hypothesis

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17
Q

Define the term specific

A

The active site is only complementary to one type of substrate.

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18
Q

Explain why an enzyme only catalyses one type of reaction.

A

Because for an enzyme to work the substrate has to fit into the active site- its shape has to be complementary. If the shape doesn’t match the active site the reaction won’t be catalysed.

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19
Q

State the sequence of events in an enzyme-controlled reaction.

A

A substrate binds to the active site forming an enzyme-substrate complex- lowers activation energy.

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20
Q

Describe the “lock and key” hypothesis of enzyme action.

A

The substrate fits into the enzyme int e same way a key fits into a lock- the active site and substrate have a complementary shape.

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21
Q

Describe the “induced-fit” hypothesis of enzyme action.

A

This helps to explain why enzymes are so specific and only bound to one particular substrate. The substrate doesn’t only have to be the right shape it has to make the active site change shape in the right way.
The active site changes shape slightly when the substrate binds to it, making it a tighter fit.

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22
Q

Suggest how the R-groups of amino acids are involved in catalysing reactions.

A

The R-groups contain features which are responsible for the tertiary structure. The tertiary structure determines the active site shape.

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23
Q

Define the term “activation energy”

A

The energy required to initiate a reaction

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24
Q

Define the term “rate of reaction”.

A

The speed at which a chemical reaction proceeds.

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25
Q

Draw an energy-level graph to show how a reaction progresses with and without an enzyme present (the transition state model).

A

With an enzyme the peak is lower and it declines faster.

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26
Q

State what the presence of an enzyme does to the activation energy for the reaction and explain why this increases the rate of reaction.

A

It lowers the activation energy:
If two substrate molecules need to be joined attaching to the enzyme holds them close together, reducing any repulsion between the molecules so they can bond more easily.
if the enzyme is catalysing a breakdown reactions fitting into the active site puts a strain on bonds in the substrate. This strain means the substrate molecules break up more easily.

27
Q

State 5 factors that affect the rate of an enzyme controlled reaction.

A
  1. Temperature
  2. Surface area
  3. Concentration of substrate
  4. Concentration of enzymes
  5. PH
28
Q

Draw a graph showing how the total amount of product produced from an enzyme-controlled reaction changes over time following the start of an experiment. Explain the shape of the graph and explain the significance of the gradient of the line at any one point.

A

It increases rapidly at the start then plateaus out quickly.

This is because at the start there is a high substrate concentration, but this falls as more reacts.

29
Q

Draw a graph showing how temperature affects the initial rate of an enzyme-controlled reaction.

A

The graph goes up then down. The peak is the optimum temperature. Not symmetrical slower incline than decline.

30
Q

Explain how temperature affects the rate of an enzyme-controlled reaction.

A
  1. More heat means more kinetic energy, so molecules move faster.
  2. Means substrate molecules more likely to collide with active sites of enzymes.
  3. The energy of these collisions also increases- so each collision is more likely to result in a reaction.
  4. The rate increases until the enzyme reaches its optimum temperature, where the rate is at it’s fastest.
  5. Past this temperature the enzyme’s molecules vibrate more, and these vibrations break some of the bonds that hold the enzyme in shape.
  6. The active site changes shape and the enzyme and substrate no longer fit together. Enzyme- denatured
31
Q

Define the term “temperature coefficient, Q10” and state its usual value for enzyme controlled reactions.

A

It is the value for a reaction showing how much the rate of reaction changes when the temperature is raised by 10 Celsius.
Before the optimum temp, a Q10 value of 2 means the rate has doubled, a value of 3 means the rate has trebled.
Most enzyme controlled reactions have a Q10 value of 2.

32
Q

Draw a graph showing how pH affects the initial rate of an enzyme-controlled reaction.

A

A symmetrical graph with the peak at the optimum pH. It is a curved line up and down.

33
Q

Explain why a pH change away from the optimum decreases the rate of reaction.

A

Above and below the optimum temperature the H+ ions and the OH- ions can break the ionic and hydrogen bonds that hold the enzyme’s tertiary structure in place. This changes the shape of the active site, so the enzyme is denatured.

34
Q

Draw a graph showing how substrate concentration affects the initial rate of an enzyme-controlled reaction.

A

The graph increases in a straight line and then curves and plateaus.

35
Q

Define the term “Vmax”.

A

The maximum rate of velocity of an enzyme catalysed reaction.

36
Q

Explain how increasing the substrate concentration affects the initial rate of an enzyme-controlled reaction.

A
  1. The higher the substrate concentration the higher the rate of reaction.
  2. More substrate molecules mean a collision between substrate and enzyme is more likely, so more active sites will be occupied and more enzyme-substrate complexes will be formed.
  3. This is only true up to a certain point.
  4. After that there are so many substrate molecules that the enzymes have about as much as they can cope with- all the active sites are full.
  5. So adding more makes no difference- enzyme concentration becomes the limiting factor.
37
Q

Draw a graph showing how enzyme concentration affects the initial rate of an enzyme-controlled reaction.

A

It is just a straight line

If the substrate amount is limited it plateaus.

38
Q

Explain how increasing the enzyme concentration affects the initial rate of an enzyme-controlled reaction.

A
  1. The more enzyme molecules there are the more like a substrate molecule is to collide with one and form an enzyme-substrate complex.
  2. Increasing the concentration of enzyme increases the rate of reaction.
  3. But if the substrate amount it limited there comes a point when there’s more than enough enzyme molecules to deal with all the available substrate.
  4. So adding more enzyme has no further effect.
39
Q

Describe and explain how to investigate any of the factors that affect the rate of enzyme-controlled reactions.

A
  1. Set up boiling tubes containing the same volume and concentration of H202.
  2. To keep pH constant add equal volumes of suitable buffer solution to each boiling tube.
  3. Have a trough of water with an upside down measuring cylinder in it. A delivery tube leading to a boiling tube with a bung.
  4. Put each tube in water baths at different temperatures along with another tube of catalase. leave for 5 mins
  5. use a pipette to add the same of catalase to each boiling tube. then add the bung .
  6. Record how much oxygen is produced in the first min.
  7. calculate the mean rate of reaction at each temperature by dividing oxygen produced by time taken.
    Change different factors accordingly.
40
Q

Explain how to find the rate of reaction from a curved graph

A
  1. Draw a tangent at the point needed.
  2. Calculate the gradient of the tangent- change in y/ change in x
  3. Work out units by doing units of y/ units of x e.g cm3 /s = cm3s-1
41
Q

Define the term cofactor

A

A non-protein substance which binds to an enzyme and activates it. It can be organic or inorganic.

42
Q

Define the term coenzyme

A

A non-protein compound that is necessary for the functioning of an enzyme.- an organic cofactor
They are changed in the reactions- act as a second substrate.
Act as carriers moving in chemical groups between different enzymes.

43
Q

Define the term prosthetic group

A

A co factor that is tightly bound to an enzyme. A permanent feature of a protein.

44
Q

Explain why the chloride ion necessary for the correct formation of the active site in amylase is called a cofactor not a coenzyme or prosthetic group.

A

Because it is inorganic so can’t be a coenzyme and is not a permanent feature of the protein.

45
Q

Explain why the zinc ion that forms an important part of the structure of carbonic anhydrase (an enzyme necessary of the metabolism of carbon dioxide) is called a prosthetic group not a cofactor or coenzyme.

A

The zinc ions are a permanent part of the enzyme’s active site.

46
Q

Give two examples of coenzymes that are synthesised from vitamins in our diet.

A

The coenzyme NAD is derived from vitamin B3.

NADP is also derived from vitamin B3.

47
Q

Define the terms “enzyme inhibitor”

A

Inhibitors are molecules that prevent enzymes from carrying out their normal function of catalyses or slow them down

48
Q

Define the terms “competitive inhibitor”

A

A molecule with a similar shape to that of a substrate, so it competes with the substrate to bind to the enzyme’s active site.

49
Q

Define the terms “non-competitive inhibitor”,

A

A molecule that binds to an enzyme away from its active site. This changes the shape of the active site so the substrate ca no longer bind.

50
Q

Define the terms reversible inhibitor

A

It doesn’t bind permanently to an enzyme

51
Q

Define the terms irreversible inhibitor

A

It binds permanently to an enzyme.

52
Q

Define the term allosteric site

A

The place on an enzyme where a molecule that is not a substrate may bind, thus changing the shape of the enzyme and influencing its ability to be active.

53
Q

Explain how a competitive inhibitor affects the rate of an enzyme-controlled reaction.

A

Thye have a similar shpae to that of substrate molecules. They compete with the substrate molecules to bind to the active site, but no reaction takes place. Instead they block the active site, so no substrate molecules can fit in.
If there is a high concentration of the inhibitor then it’ll take up nearly all the active sites.
Slows the rate of reaction

54
Q

Explain how a non-competitive inhibitor affects the rate of an enzyme-controlled reaction.

A

The inhibitor binds to the enzyme away from its active site. The site they bind to is the allosteric site. This causes the active site ti change shape so the substrate molecules can no longer bind to it.
Increasing the substrate concentration won’t make any difference as enzyme activity is still inhibited

55
Q
  1. Draw graph showing how substrate concentration affects the rate of an enzyme-controlled reaction if a competitive or non-competitive inhibitor is present. Explain the effect of competitive and non-competitive inhibitors on the Vmax of an enzyme-controlled reaction.
A

Competitive- the line is under the original and straighter but still reaches the same maximum.
Non-competitive- the line is much lower and plateaus at a much lower point. So has a smaller maximum.

56
Q

Define the term “end-product inhibition” and describe its usefulness in controlling metabolic pathways.

A

Metabolic pathways are regulated by end-product inhibition. A metabolic pathway is a series of connected metabolic reactions. The product of the first reaction takes part in the second. Each reaction is catalysed by a different enzyme. Many enzymes are inhibited by the product of the reaction they catalyse- product inhibition.
End product inhibition- when the final product in a pathway inhibits an enzyme that acts earlier on in its pathway.

57
Q

Describe how ATP is involved in end-product inhibition of the enzyme phosphofructokinase.

A

phosphofructokinase is an enzyme in the metabollic pathway that breaks down glucose to make ATP. ATP inhibits the action of phosphofructokinase- so a high level stops more being made

58
Q

Define the term “inactive precursor enzyme” and explain why enzymes may be produced in this form.

A

Enzymes are sometimes synthesised as inactive precursors in metabolic pathways to prevent them causing damage to cells. Part of the precursor molecule inhibits its action as an enzyme. Once this part is removed the enzyme becomes active.

59
Q

Describe three ways in which inactive precursor may be activated.

A

For a precursor to be active it needs to undergo a change in tertiary structure by:

  1. By the addition of a co-factor
  2. The action of another enzyme e.g protease
  3. changing conditions- temp or pH level.
60
Q

Define the term apoenzyme

A

An apoenzyme is an inactive enzyme, activation of the enzyme occurs upon binding of an organic or inorganic cofactor.
It is the name of a precursor enzyme before a cofactor is added

61
Q

Define the term holoenzyme

A

A biochemically active compound formed by the combination of an enzyme with a coenzyme.
The name of a precursor protein once it has be activated by the binding of a cofactor

62
Q

Define the term zymogens

A

An inactive substance which is converted into an enzyme when activated by another enzyme.

63
Q

Define the term proenzyme

A

A biologically inactive substance which is metabolized into an enzyme.

64
Q

There are two models for the mechanism of enzyme action. Outline how changes in temperature can affect these mechanisms of lipase action

A
  1. Enzyme-substrate complex is formed and then enzyme-product complex formed
  2. Product will leave the active site.
  3. Lock and key= shape of substrate and enzyme’s active site are complementary and so enzyme is specific.
  4. Induced fit= enzyme active site changes shape to accommodate substrate once substrate binds.
  5. Increase in temperature increases kinetic energy of molecules which results in more successful collisions, so more enzyme-substrate complexes form.
  6. Decrease in temperature reduces kinetic energy of molecules, results in fewer successful collisions so fewer enzyme substrate complexes are formed.
  7. Enzymes have an optimum temperature
  8. An increase in temperature affects the bonds involved in the tertiary structure, which changes the shape of the active site.
  9. This prevents substrate binding to active site.
  10. High temperature results in denaturing.
  11. Affects of high temperature are irreversible
  12. Affects of low temperature are reversible

A level- Biology (46 decks)

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