3.1.3 Biochemical Reactions in Cells are Controlled by Enzymes Flashcards Preview

A-level Biology Oxford AQA > 3.1.3 Biochemical Reactions in Cells are Controlled by Enzymes > Flashcards

Flashcards in 3.1.3 Biochemical Reactions in Cells are Controlled by Enzymes Deck (50)
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1

 Enzymes can affect ______ and _____ in organisms

Enzymes can affect structures and functions in organisms

2

 Enzymes are highly specific due to their ____ _______

tertiary structure

3

Explain how forming an enzyme-substrate complex lowers activation energy

  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

4

How is a substrate molecule held within an active site?

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

5

Describe the 'lock and key' model

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

6

What is the problem with the 'lock and key' model?

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

7

What model is better than the 'lock and key' model?

'Induced Fit' Model

8

Why do enzymes only bond to one particular substrate?

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

9

Why are enzymes very specific?

∵ only one complementary substrate will fit into their active site

10

Each enzyme has a different tertiary structure ∴ ... 

It has a different shaped active site

11

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

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

12

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

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

13

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

  • 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

14

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

  • 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

15

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

  • 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

16

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

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

17

Explain what happens to enzymes when they get too hot

  • 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

18

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

  • 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)

19

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

  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

20

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

decrease over time

21

Why does the rate of reaction decrease over time?

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

22

The initial rate of reaction is the... 

highest rate of reaction

23

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

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

24

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

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

25

How can enzyme activity can be prevented?

By enzymes inhibitors

26

Describe how a competitive inhibitor prevents enzyme activity

  • 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

How much enzyme is inhibited depends on... 

relative concentration of inhibitor and substrate

28

Competitive Inhibition 

What happens if you increase the concentration of the inhibitor?

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

29

Competitive Inhibition 

What happens if you increase the concentration of the substrate?

  • Substrate's chance of getting to active site before inhibitor increase
  • Increases rate of reaction

30

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

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