3.1.3 Biochemical Reactions in Cells are Controlled by Enzymes Flashcards

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1
Q

Enzymes can affect ______ and _____ in organisms

A

Enzymes can affect structures and functions in organisms

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2
Q

Enzymes are highly specific due to their ____ _______

A

tertiary structure

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3
Q

Explain how forming an enzyme-substrate complex lowers activation energy

A
  1. If 2 substrate molecules need to be joined:
    1. Being attached to the enzyme holds them close together = reducing any repulsion between molecules
    2. ∴ they bond more easily
  2. If enzyme is catalysing a breakdown reaction:
    1. Fitting into the active site puts a strain on bonds in substrate
    2. ∴ substrate molecule breaks up more easily
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4
Q

How is a substrate molecule held within an active site?

A

By bonds that form temporarily between amino acids of active site and groups on substrate molecules

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5
Q

Describe the ‘lock and key’ model

A

Where substrate fits into enzyme in the same way a key fits into a lock

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6
Q

What is the problem with the ‘lock and key’ model?

A

Too simplistic = enzyme-substrate complex actually CHANGES shape slightly to complete the fit

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7
Q

What model is better than the ‘lock and key’ model?

A

‘Induced Fit’ Model

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8
Q

Why do enzymes only bond to one particular substrate?

A

∵ substrate has to be right shape (complementary) to fit active site & has to make active site CHANGE SHAPE

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9
Q

Why are enzymes very specific?

A

∵ only one complementary substrate will fit into their active site

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10
Q

Each enzyme has a different tertiary structure ∴ …

A

It has a different shaped active site

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11
Q

How might a mutation in a gene affect the stucture of an enzyme?

A
  • Primary structure is determined by gene
  • If mutation occurs in gene = could change tertiary structure of enzyme produced
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12
Q

How can a change in the primary structure affect an enzyme?

A
  • Sequence of amino acids changes
  • Bonds form in different places as it alters hydrogen, disulfide, ionic bonds
  • Tertiary structure changes
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13
Q

Describe how tertiary structure of a protein determines the shape of an active site (3)

A
  • Primary structure: unique sequence of amino acids
  • Different arrangement of R groups determine how it’ll fold into the secondary structure & then tertiary structure
  • Tertiary structure determines 3D shape & shape of active site
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14
Q

Explain in terms of primary structure why an enzyme is usually specific to one substrate (4)

A
  • Primary structure: unique sequence of amino acids
  • Different arrangement of R groups determine how it’ll fold into the secondary structure & then tertiary structure
  • Tertiary structure = specific 3D shape & active site is apart of this shape (made up of around 10 amino acids)
  • Certain R groups will be exposed that allow substrate to bind
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15
Q

Explain why increasing the temperature increases rate of reaction (enzyme activity)?

A
  • More heat = more kinetic energy so molecules move faster
    • ∴ enzymes more likely to collide with substrate molecules
    • Energy of collisions increase = collisions more likely to result in reaction (be successful)
  • More enzyme-substrate complexes form
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16
Q

What happens to the rate of reaction when the temperature is too low (enzyme activity)?

A
  • Little kinetic energy = little movement
  • Substate won’t collide with active site = rate of reaction decreases
  • Less enzyme-substrate complexes form
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17
Q

Explain what happens to enzymes when they get too hot

A
  • Lots of kinetic energy = enzymes vibrate too much
  • This breaks some of bonds (e.g. weaker hydrogen/ionic) that hold enzyme in shape
  • Changes in tertiary structure
  • Active site changes shape
  • Enzyme substrate complex can’t form
  • Enzyme = denatured
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18
Q

What happens when an enzyme is placed in a solution that is above or below its optimum pH?

A
  • H+ and OH- ions found in acids/alkalis form extra/break ionic & hydrogen bonds that hold enzyme’s tertiary structure
    • Active site change shape ∴ enzyme = denatured
  • (Happens ∵ ions can bind to any negatively charged R groups active site)
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19
Q

Describe and explain how increasing the substrate concentration affects the rate of a reaction

A
  1. Increases rate of reaction
    • ∵ More substrate molecules = more collisions between substrate & enzymes = more enzyme substrate complexes
  2. BUT up to a ‘saturation’ point where it then levels off
    • ∵ active sites are full
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20
Q

If the substrate concentration decreases with time then the rate of reaction will…

A

decrease over time

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21
Q

Why does the rate of reaction decrease over time?

A

∵ fewer substrate molecules to collide with enzymes & products may ‘get in the way’ of substates reaching active site

22
Q

The initial rate of reaction is the…

A

highest rate of reaction

23
Q

Why does increasing the concentration of enzymes increase the rate of the reaction?

A

More enzymes molecules in solution = more likely for substrate molecules to collide with one & form enzyme-substrate complex

24
Q

What happens to rate of reaction if the amount of a substrate is limited, when increasing the enzyme concentration, & why?

A

Comes to a point where there’s more than enough enzymes to deal with available substrates = so rate of reaction levels off

25
Q

How can enzyme activity can be prevented?

A

By enzymes inhibitors

26
Q

Describe how a competitive inhibitor prevents enzyme activity

A
  • Competitive inhibitor molecules have similar shape of substrate molecules
  • Compete with substate molecules to bind to active site
  • They block the active site = no substrate molecules can fit
  • Less enzyme substrate complexes can form
27
Q

How much enzyme is inhibited depends on…

A

relative concentration of inhibitor and substrate

28
Q

Competitive Inhibition

What happens if you increase the concentration of the inhibitor?

A
  • They take up nearly all active sites (little substate will get to enzyme)
  • Decreases rate of reaction
29
Q

Competitive Inhibition

What happens if you increase the concentration of the substrate?

A
  • Substrate’s chance of getting to active site before inhibitor increase
  • Increases rate of reaction
30
Q

Sketch a graph to show how increasing the substrate concentration affects the rate of the reaction

A
31
Q

Sketch a graph to show how increasing the enzyme concentration affects the rate of the reaction

A
32
Q

Describe how a non-competitive inhibitor affects an enzyme

A
  1. Non-competitive inhibitor binds to enzyme away from its active site
  2. This causes active site to change shape so substate molecules can’t bind to it
  3. i.e. Tertiary structure changes
  4. No enzyme substrate complexes can form
33
Q

Why are non-competitive inhibitors different shapes?

A

∵ they don’t compete

34
Q

Non-Competitive Inhibition

Does increasing the concentration of substrate affect the rate of the reaction?

A

NO

35
Q

Sketch graph showing an enzyme-controlled reaction without an inhibitor and the same reaction with a competitive inhibitor

A
36
Q

Sketch graph showing an enzyme-controlled reaction without an inhibitor and the same reaction with a non-competitive inhibitor

A
37
Q

Name 2 ways you can measure the rate of an enzyme-controlled reaction

A
  1. You can measure how fast the product of reaction is made
  2. You can measure how fast the substrate is broken down
38
Q

How can you investigate the effect of pH on an enzyme-controlled reaction? (brief answer needed)

A

By adding a buffer solution with a different pH to each test tube

39
Q

How can you investigate the effect of substrate concentration on an enzyme-controlled reaction? (brief answer needed)

A

Use serial dilutions to make substrate solutions with different concentrations

40
Q

Casein is protein found in milk & _____ is the enzyme that digests it

A

Trypsin

41
Q

When trypsin is added to a _____ _____ of ___ ____, casein is digested and solution goes ____

A

When trypsin is added to a dilute solution of milk powder, casein is digested and solution goes clear

42
Q

Describe how you can investigate the effect of temperature on the rate of an enzyme-controlled reaction

A
  1. Draw ‘X’ halfway down each of the 3 test tubes
  2. Add 10 cm3 of solution of milk powder to each test tube
  3. Add 2cm3 of trypsin & 2cm3 of pH 7 buffer to another 3 test tubes
  4. Put all 6 test tubes into water bath at 20°C for 10 minutes
  5. Add trypsin and buffer solution to solution of milk powder
    1. Place bung in them and invert it 5 times
  6. Place it back into water bath & time how long it takes for milk to clear (i.e. until you see the ‘X’)
    1. Record this time
  7. Use same method to find out how long it takes trypsin to digest the protein at 30°C, 40°C, 50°C, 60°C
43
Q

When interpreting graphs about enzyme-controlled reactions, what should you look at first?

A

The initial rate of reactions

44
Q

At 37°C, why does the graph plateau?

A

∵ all the substrate has been used up

45
Q

At 65°C, why does the graph plateau earlier than 37°C?

A
  • ∵ the high temperature = enzyme denatured so reaction stopped sooner
  • Not as much product was made ∵ not all substrate was converted to product (before the enzyme was denatured) so there’s still substrate left
46
Q

What is happening at 25°C and why?

A

Rate of reaction is remaining constant and the volume of product is continuing to increase ∵ not all of the substrate has been used up

47
Q

Describe how you would calculate the initial rate of a reaction

A
48
Q

Explain why maltase only catalyses the hydrolysis of maltose (3)

A
  1. Active site of maltase has specific shape/tertiary structure which is complementary to maltose
  2. Only maltose can bind to it
  3. To form enzyme substrate complex
49
Q

Suggest 3 reasons why it is more efficient to attach lactase to beads than adding it directly to cow’s milk

A
  • (Lactase/beads) can be reused
  • No need to remove from milk
  • Allows continuous process
  • The enzyme is more stable
  • Avoid end product inhibition
50
Q

Describe the induced fit model of enzyme action (3)

A
  • Active site / enzyme not complementary
  • Active site changes (shape) / is flexible
  • (Change in enzyme allows) substrate to fit / E-S complex to form