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Wjec Biology As Unit 1 > 1.4 Enzymes > Flashcards

1.4 Enzymes Flashcards

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1
Q

Why do enzymes only catalyse one reaction?

A

The active site of the enzyme has a specific shape

The substrate has a complementary shape and therefore binds into the active site

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2
Q

How does a competitive inhibitor work?

A

It has a similar shape to the substrate
It had a complementary shape to the active site
It binds to the active site
When it does bind it prevents the substrate from doing so
Fewer enzyme-substrate complexes formed

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3
Q

Describe and explain the effect of temperature on the rate of activity of an enzyme

A
  • increase in rate along with increase in temperature up to optimum due to increased kinetic energy so molecules move faster and more successful collisions/ more enzyme-substrate complexes formed
  • at temperatures above optimum there are increased vibrations which cause the Hydrogen bonds to break and the tertiary structure changes and a change of shape of the active site and the enzyme is DENATURED
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4
Q

Factors affecting enzyme activity (5)

A 
Inhibitors
Temperature 
pH
Concentration of substrate 
Concentration of enzyme
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5
Q

Distinguish between intracellular and extracellular enzymes

A

Intra - work inside the cell

Extra - work outside the cell

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6
Q

Advantages of immobilised enzymes

A
  • greater stability over a wider range of temperature and pH
  • products are easily recovered
  • products aren’t contaminated with the enzyme
  • enzymes are easily added or removed
  • more than 1 enzyme may be used
  • enzymes can be reused
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7
Q

Enzymes are biological catalysts. What does this mean?

A

Biological - produced by cells and is a protein

Catalyst - speed up rate of reaction without being used up

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8
Q

What is metabolism

A

Series of enzyme-controlled reactions in the body

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9
Q

Anabolic reactions

A

Building up molecules
Requires ATP
Eg protein synthesis

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10
Q

Catabolic reaction

A

Breaking down molecules
Releases energy
Eg digestion of proteins

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11
Q

Key point about enzymes

A
  • speed up chemical reactions
  • lower the activation energy
  • dont take part in the reaction
  • needed in small quantities
  • can be reused
  • convert substrates into products
  • biological catalysts
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12
Q

Describe the structure of enzymes

A
  • tertiary structure that is held by Hydrogen, ionic and disulphide bonds
  • creates an active site where substrate can bind
  • act in aqueous environments as they’re soluble and can catalyse hydrolysis
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13
Q

Intracellular

A

Work inside the cell

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14
Q

Extracellular

A

Work outside the cell

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15
Q

What is an enzyme-substrate complex

A

Temporary complex when an enzyme binds to a substrate such that the substrates are close enough to react

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16
Q

What is the active site

A

Small region on the enzyme where the substrate binds

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17
Q

Lock and key model

A
  • substrate has a complementary shape to the enzyme’s active site
  • explains enzyme specificity
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18
Q

Induced fit theory

A
  • suggests the active site of enzyme may not exactly correspond to the substrate
  • enzyme’s shape alters slightly to accommodate substrate
  • enzyme will revert back to ‘relaxed’ state after the products are formed and repelled
  • suggests enzyme is flexible and not rigid
19
Q

How do enzymes work

A

Lowering the activation energy needed to make chemical reactions to start

20
Q

Factors affect the rate of enzyme action

A
  • substrate concentration
  • temperature
  • pH
  • enzyme concentration
  • presence of inhibitors
21
Q

What is inactivation

A

Reversible reduction of enzyme activity at low temperature as molecules have insufficient kinetic energy to from enzyme-substrate complexes

22
Q

What is denatured

A

Permanent changes to the shape of the active site which prevents the substrate from binding

23
Q

Describe the effect of substrate concentration on enzyme activity

A 
Low concentration = low rate
• limits chance of successful collisions 
• is a limiting factor
High concentration = high rate
• greater chance of successful collisions resulting in more enzyme-substrate complexes
Plateau = highest rate
• enzyme active sites are saturated 
• no longer a limiting factor
24
Q

Describe effect of temperature on enzyme activity

A

Low temperature = low rate
• enzyme is inactivated
• insufficient kinetic energy so few successful collisions
Increase in temperature up to optimum = increase in rate
• increase in KE
•increases chance of successful collisions so more enzyme-substrate complexes
Temperature above optimum = rapid decrease
• hydrogen bonds break due to increased vibrations
• shape of active site changes and enzyme is denatured
• no successful collisions

25
Q

Describe the effect of pH on enzyme activity

A

pH increases or decreases either side of the optimum = decreases rate
• charges on R group on AA on active site are influenced by H+ and OH-
• if too many H+ or OH- the substrate can be repelled from the active site which stops it from binding
• small changes - reversible
• excessive changes - ionic bonds break which denatures the enzyme

26
Q

Look

A
27
Q

Look

A
28
Q

Look

A
29
Q

What is a limiting factor

A

Increase in it’s value causes an increase in the rate of reaction

30
Q

Describe affect of enzyme concentration on enzyme activity

A
  • as they can be reused only a low concentration is needed to catalyse a large number of reactions
  • as long as the temperature and pH are suitable and there’s an excess of substrate then the rate will be directly proportional to the enzyme concentration
31
Q

Look

A
32
Q

Reversible inhibition

A

Inhibitor binds temporarily

33
Q

Irreversible inhibition

A

Inhibitor binds permanently

34
Q

Describe a competitive inhibitor

A
  • molecular shape complementary to the active site and similar to the substrate
  • competes with the substrate for the active site
  • when it does bind to the active site it prevents the substrate from binding which decreases the rate of reaction
  • reversible
  • increasing substrate concentration will decrease the effect as it is more likely that a substrate molecule will form an enzyme-substrate complex
  • increasing inhibitor concentration will decrease the rate of reaction but the final mass of product ends up the same
35
Q

Describe non-competitive inhibitor

A
  • binds to the enzyme at an allosteric site and changes the shape of the enzyme
  • doesn’t compete with substrate
  • changes the overall shape of the enzyme which means the substrate can no longer bind and no enzyme-substrate complexes are formed
  • can be reversible or irreversible
  • increasing substrate concentration doesn’t reduce inhibition
  • increasing inhibition concentration decreases rate of reaction and decreases final mass of product formed
36
Q

What is an immobilised enzyme

A

Enzyme molecules bound to an inert material, over which the substrate molecules move

37
Q

Name ways of immobilising enzymes

A
  • alginate beads

* cellulose microfibrils

38
Q

How can being able to control the rate of flow of the substrate over the beads be used

A

Slowing the flow rate will give more time for enzyme-substrate complexes to form and so yield more product

39
Q

How does being in a ‘micro-environment’ affect the enzymes activity

A

The enzymes are less susceptible to changes in pH, temperature and the action of chemicals such as organic solvents

40
Q

Advantages of immobilising enzymes

A
  • enzymes easily recovered and reused
  • product is not contaminated by the enzyme
  • increased stability and function over a wider range of temperature and pH than free enzymes
  • several enzymes with different temperature and pH optima can be used at the same time
  • enzymes can be easily added or removed- greater control over the reaction
41
Q

What is a biosensor

A

A device that combines a biomolecule, such as an enzyme, with a transducer, to produce an electrical signal which
measures the concentration of a chemical.

42
Q

What is the role of the selectively permeable membrane in a biosensor

A

Allows the metabolite to diffuse through to the immobilised enzyme, whilst preventing the passage of other molecules

43
Q

How does a biosensor turn the metabolite into an electrical signal

A
  • binds to the active site of enzyme and turns into product

* product combines with the transducer which turns the chemical energy into an electrical signal

Wjec Biology As Unit 1 (7 decks)

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