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a level biology > 3.1.4.2 enzymes > Flashcards

3.1.4.2 enzymes Flashcards

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1
Q

what are enzymes?

A
  • biological catalyst which speeds up the rate of reaction by providing an alternative pathway using lower activation energy.
  • enzymes are never used up.
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2
Q

what type of proteins are enzymes?

A

globular proteins.

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3
Q

examples of intracellular enzymes?

A
  • inside the organism.
    = ATPase.
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4
Q

examples of extracellular enzymes?

A
  • outside the organism.
    = saphotrophic nutrition.
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5
Q

how is the shape of the active site determined?

A
  • determined by the primary structure.
  • a long chain of amino acids in which the order and sequence of amino acids are key as the R groups and the bonding between them causes the chain to fold up into different 3D structures.
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6
Q

what is the lock and key hypothesis?

A
  • it’s the idea that the active site of an enzyme and the substrate are a perfect fit for each other and are COMPLEMENTARY.
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7
Q

what is the induced fit hypothesis?

A
  • it’s the idea that the active site changes shape and moulds around the substrate.
  • initially, the substrate and active site are not complementary.
  • when the active site and substrate bind a conformational change is induced.
  • when the products have been made the active site returns to its original shape.
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8
Q

how do enzymes use a lower activation energy?

A
  • in the induced fit hypothesis the change in shape of the active site causes a strain in the bonds.
  • this strain weakens the bonds and causes a lower activation energy as the bonds will now require less energy to be broken.
  • this increases the rate of reaction and causes more enzyme-substrate complexes to be formed.
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9
Q

what is the effect of temperature on the rate of enzyme-controlled reactions?
(up to the optimum temp)

A
  • an increase in temperature causes an increase in kinetic energy.
  • an increase in kinetic energy causes more frequent collisions between enzymes and substrates.
  • meaning more enzyme-substrate complexes are formed.
  • meaning more products are formed.
  • causing an increase in the rate of reaction.
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10
Q

what is the effect of temperature on the rate of enzyme-controlled reactions?
(over the optimum temp)

A
  • the kinetic energy is so great that it breaks london forces and hydrogen bonds, which hold together the 3D structure of enzymes.
  • this causes the shape of the active site to change.
  • this results in the active site no longer being complimentary to the substrate, therefore they won’t be able to bind.
  • no enzyme-substrate complexes will be formed.
  • causing the enzyme to denature permanently.
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11
Q

what is the effect of pH on the rate of enzyme-controlled reactions?
(at optimum pH)

A
  • the optimum pH of enzymes varies between enzymes.
  • at optimum pH the enzyme’s active site is complementary to the substrate shape and change.
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12
Q

what is the effect of pH on the rate of enzyme-controlled reactions?
(changing pH)

A
  • change in pH away from the optimum causes the rate of reaction to decrease.
  • ionic forces and hydrogen bonds get disrupted.
  • this causes a change in the 3D and tertiary structure.
  • the active site changes shape and becomes no longer complementary to the substrate.
  • no enzyme-substrate complexes can be formed.

slight changes in the pH changes the bonding, however, is REVERSIBLE.

extreme changes in the pH denatures the enzyme.

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13
Q

what is the effect of the concentration of substrate on the rate of enzyme-controlled reactions?
(before all active sites are occupied)

A
  • as the substrate concentration increases the rate also increases.
  • this is as more enzyme substrate collisions occur.
  • the maximum rate is when all active sites are occupied.
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14
Q

what is the effect of the concentration of substrate on the rate of enzyme-controlled reactions?
(when all active sites are occupied)

A
  • any further increase in the concentration of the substrate has no effect.
  • this is because there are no free active sites so no enzyme-substrate complexes can be formed.
    = the enzymes (active sites) are the limiting factors.
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15
Q

what is the effect of the concentration of enzymes on the rate of enzyme-controlled reactions?
(at a fixed substrate concentration)

A
  • at very high enzyme concentrations the concentration of substrates becomes the limiting factor.
  • this is due to all the substrate molecules being used.
  • therefore any further increase in enzyme concentration has no effect.
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16
Q

what is the effect of the concentration of enzymes on the rate of enzyme-controlled reactions?

A
  • as you increase the enzyme concentration, the rate of reaction also increases.
  • this is due to the number of active sites available increasing.
  • this results in more enzyme-substrate collisions, therefore more enzyme-substrate complexes being formed.
  • the maximum rate will be reached when all substrates react instantly.
17
Q

how do competitive inhibitors work?

A
  • the competitive inhibitor is a similar shape to the substrate.
  • therefore, the competitive inhibitor is complementary to the active site.
  • the inhibitor binds with the active site to form the enzyme-inhibitor complex, which blocks the enzyme.
18
Q

how do competitive inhibitors affect the rate of enzyme-controlled reactions?

A
  • the inhibitor binds with the active site to form the enzyme-inhibitor complex, which blocks the enzyme.
  • therefore reducing the number of active sites available for the substrate.
  • how much the rate is affected by the competitive inhibitor depends on the concentration of substrate, as the two are competing for the active site.
19
Q

how do non-competitive inhibitors work?

A
  • non-competitive inhibitors do not bind to the active site unlike competitive inhibitors, therefore they are not competing with the substrate.
  • the non-competitive inhibitors bind to the allosteric site.
  • this binding causes a change in the 3D tertiary structure of the enzyme, which causes a change in the active site.
  • therefore, fewer enzyme-substrate complexes can be formed as the substrate cannot bind.
  • therefore the rate of reaction decreases.
  • the concentration of substrate has no effect on the rate of reaction.
20
Q

what is end-product inhibition?

A
  • when the final product of a pathway binds to the allosteric site on the first enzyme in the pathway.
  • this causes a change in the 3D shape and the tertiary structure of the enzyme.
  • the active site will change shape.
  • when the final product detaches from the allosteric site the enzyme will return to its original shape = allowing the pathway to resume.

a level biology (11 decks)

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