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A level Biology Paper 1- Core concepts > Enzymes > Flashcards

Enzymes Flashcards

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1
Q

What must cells do to stay alive?

A

-many biochemical reactions to breakdown larger molecules into smaller molecules and build up smaller molecules into
larger molecules

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2
Q

what are these biochemical reactions collectively called?

A

Metabolism

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3
Q

what type of proteins are enzymes?

A

Globular Proteins

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4
Q

What structure do proteins have?

A

-specific tertiary structure held by hydrogen bonds, ionic bonds, disulphide bridges and hydrophobic interactions

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5
Q

what do enzymes act as?

A

biological catalysts- this means they speed up the rate of metabolic reactions by lowering activation energy

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6
Q

what is activation energy?

A

The energy required for a reaction to begin

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7
Q

Where can enzymes work?

A

-enzymes can work inside our cells (intracellular) or outside our cells (extracellular)

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8
Q

What are the two ways that enzymes can catalyse metabolic reactions?

A

-Anabolic reactions
-Catabolic reactions

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9
Q

What part of the enzyme is functional?

A

-although the molecule is large, only a small region called the active site is functional

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10
Q

what are the two main models for enzyme action?

A

-Lock and key model
-Induced fit model

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11
Q

What is the lock and key model?

A

• The substrate molecule fits into the active site of the enzyme molecule like a key fitting into a lock as they are complementary shapes. This forms the enzyme substrate complex.
• The product is then formed and as it no longer fits into the active site it is released.
• This model explains why enzymes are very specific, i.e. each enzyme will only catalyse

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12
Q

What is the induced fit model?

A

The substrate and the active site of the enzyme are not complementary shapes.
• When a substrate molecule binds to the active site, the active site changes shape and fits itself around the substrate.
• This places a strain on the substrate molecule and distorts a particular bond, lowering the activation energy required to break the bond.
• The products are formed and leave the active site which then returns to its original shape.

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13
Q

What is an example of and enzyme for induced fit?

A

Lysozyme

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14
Q

what is induced fit for lysozyme?

A

-Lysosome’s active site is not perfectly complimentary to the substrate
-Lysosome’s active site changes shape to fit the substrate
-This lowers the activation energy for the reaction to occur
-The products are released and the lysosome’s active site returns to its original shape

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15
Q

What does the enzyme lysozyme do?

A

-helps kill bacteria by catalysing the hydrolysis of sugars in the peptidoglycan cell walls
-the cell walls are weakened, the bacteria absorb water by osmosis and burst

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16
Q

Where is lysozyme found?

A

-it is present in many secretions such as tears, saliva, human milk and is also found in lysosomes

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17
Q

Why are enzymes specific?

A

Due to the sequence of amino acids that make up their active site

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18
Q

why are enzymes soluble?

A

-as hydrophilic R groups are found in the outside of the molecules

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19
Q

Enzymes are fast acting with a very high turnover number, what does this mean?

A

-This means they can many molecules of substrate per unit time, e.g. catalase, the enzyme that hydrolyses hydrogen peroxide has a turnover number of 40 million molecules per second

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20
Q

What is the explanation for a graph showing the formation of product overtime for an enzyme controlled reaction?

A
  1. The curve is steepest as initially there is a large concentration of substrate molecules, so they are more likely to successfully collide with an active site and form the product. Initially the enzyme concentration is the limiting factor.
  2. As the reaction proceeds there is a decreasing concentration of substrate so less chance of successful collisions; now substrate concentration is the limiting factor.
  3. The graph eventually levels off as all of the substrate has been converted to product and no further product is formed
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21
Q

What does the independent variable go on a graph?

A

on the x-axis

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22
Q

What is the explanation of a graph showing the mass of substrate over time for an enzyme controlled reaction?

A
  1. Substrate concentration is at a maximum level at the start of the reaction.
  2. There is a rapid fall in the concentration of substrate. Substrate molecules bind to enzyme active sites and are converted into product.
  3. Substrate concentration is very low. All the substrate has been converted into product
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23
Q

where are enzymes synthesised?

A

inside living cells

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24
Q

where inside the cells may enzymes catalyse reactions? (intracellular)

A

-in solution
-membrane bound

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25
Q

What does it mean when enzymes catalyse reactions outside the cell?

A

they are secreted

26
Q

what environmental conditions and factors affect the rate of enzyme controlled reaction?

A

-temperature
-pH
-Substrate concentration
-Enzyme concentration
-Inhibitors (competitive or non-competitive)

27
Q

How does temperature affect the enzyme activity? (points on graph)

A
  1. The enzyme and substrate molecules have low kinetic energy
  2. increasing the temperature up to the optimum increases rate of reaction.
  3. optimum temperature , the rate of reaction is at it ‘s highest
  4. At very high temperatures the rate of reaction falls to 0
28
Q

what is the explanation of how enzyme activity is affected by temperature? (points of a graph)

A
  1. the enzyme and substrate molecules have low KE- fewer successful collisions forming fewer each
  2. The kinetic energy of the enzyme and substrate molecules increases, increasing the chance of successful
    kinetic energy. More enzyme-substrate complexes are formed.
  3. The molecules have more (too much) kinetic energy. The increasing vibrations begins to break hydrogen bonds, changing the tertiary structure of the enzyme. This alters the shape of the active site so it is no longer
    complementary to the substrate. This lowers the rate of reaction as enzyme-substrate complexes cannot form.
  4. All the enzymes are denatured.
    This is when the active site is permanently distorted (changes shape) by irreversible breaking of Hydrogen bonds, this prevents the substrate from binding as it is no longer complementary to the active site.
29
Q

What happens at the optimum pH for enzymes?

A

-The root of the reaction reaches its maximum

30
Q

What pH values can enzymes work within?

A

Narrow range of pH values

31
Q

what can small deviations from the optimum pH cause?

A

-Reversible changes in enzyme structure, resulting in inactivation

32
Q

what can extreme pH do to an enzyme?

A

permanently denature an enzyme

33
Q

what may an extreme change in the pH do? (to enzymes)

A

-Alter electrostatic charge in the side chains of the amino acids
-If the active site has too many H+ ions (acidic) or OH- ions (alkali) the active site and substrate may both have the same charge and the enzyme will repel the substrate

34
Q

What can buffers do?

A

can be added to enzyme-controlled reactions to maintain a constant pH

35
Q

What happens to the rate of reaction at fixed enzyme concentration?

A

-The rate of reaction will increase as substrate concentration increases

36
Q

what is the limiting factor at low substrate concentration and why?

A

-substrate concentration- the enzyme molecules have only a few substrate
molecules to collide with

37
Q

what happens as more substrate is added? (effect of substrate concentration)

A

-more successful collisions and more enzyme active sites become occupied, until eventually, the rate of reaction reaches a maximum and substrate molecules are in excess- the enzyme concentration becomes the limiting factor

38
Q

what happens once a product leaves the active site?

A

The enzyme molecule can be reused

39
Q

what will the rate of an enzyme-catalysed reaction vary with?

A

-changes in the enzyme concentration, as concentration increases there are more active sites available and they fall. The rate of reaction increases.

40
Q

what is the enzyme inhibition?

A

-the reduction in the rate of an enzyme- controlled reaction by another molecule
-the inhibitor combines with the enzyme and either directly or indirectly prevents it from forming an enzyme-substrate complex

41
Q

what are competitive inhibitors?

A

They interfere with an active site of an enzyme so substrate cannot bind

42
Q

What are competitive inhibitors similar shape to?

A

-Substrate

43
Q

what does a competitive inhibitor do?

A

-they are complimentary to the active site and bind to it
-this blocks the actual substrate from entering the active site and so less enzyme substrate complexes can form

44
Q

What happens to the rate of reaction due to a competitive inhibitor?

A

-rate of reaction decreases and as a result less product is produced
-if conc of substrate increases, the effect of the inhibitor is reduced

45
Q

What is an example of a competing inhibitor?

A

malonic acid

46
Q

How does Malonic acid work?

A

-In the mitochondrial matrix, a reaction involved in aerobic respiration is catalysed by the enzyme succinic dehydrogenase
-the competitive inhibitor malonic acid has a similar shape to the substrate, succinic acid

47
Q

What is a noncompetitive inhibitor?

A

-it is not a similar shape to the substrate
-It binds to the enzyme at a point other than the active site known as the allosteric site.

48
Q

What does a non competitive inhibitor binding to the allosteric site do?

A

-this changes the shape of the enzyme and therefore the shape of the active site so it no longer is complimentary to the substrate
-The enzyme molecule may be permanently damaged

49
Q

What are immobilised enzymes?

A

-enzymes that are fixed, trapped or bound on an inert matrix

50
Q

what is an example of an immobilised enzyme?

A

-an alginate bead which is non reactive

51
Q

What are examples of how enzymes are immobilised?

A

-absorption onto an insoluble matrix
-Covalent binding to a solid support
-Trapped within a gel
-Encapsulation behind a selectively permeable membrane

52
Q

Why do enzymes immobilised in beads have a lower rate of reaction than those immobilised on a membrane?

A

-some active sites are inside the beads and the substrate will take time to diffuse into them
-Enzymes on the surface have active sites that are more easily accessible so there is a higher chance of the element

53
Q

what are advantages of immobilised enzymes?

A

-Enzymes are easily RECOVERED for re-use
-Product is not contaminated with the enzyme
-Increased stability over over a wider range of pH values
-Increased stability over a range of temperatures, and enzymes denature at higher temperatures
-Several enzymes with differing temperature or pH optima can be used in one process.
-Enzymes can be easily added or removed giving greater control over the rate of reaction

54
Q

what does trapping an enzyme do?

A

Stabilises it and prevents the shape change that would denature its active site, so it can be used under wide range of conditions

55
Q

What are uses of immobilised enzymes?

A

-lactose free milk
-Bi sensors
-High fructose corn syrup

56
Q

how are immobilised enzymes used for lactose free milk?

A

-milk contains the sugar lactose, and some people are intolerant to this, as they do not possess the enzyme lactase
-lactose free milk can be produced using immobilise enzymes, trapped in an alginate bead in a column to hydrolyse the lactose to its monosaccharides, glucose and galactose

57
Q

what are biosensors?

A

-these devices convert a chemical signal into an electrical signal
-The rapidly detect and measure very low concentrations of a specific substrate in a complex mixture

58
Q

what is one particular use of immobilised enzymes of a biosensor?

A

-The measurement of glucose concentration in blood samples
-the enzyme glucose oxidise is immobilised on a selectively permeable membrane, when placed in a sample the enzyme binds to glucose, a small electrical current is produced and detected by an electrode. The concentration of glucose can then be read on a screen.

59
Q

what is one medical condition that can be detected using a glucose biosensor?

A

Diabetes

60
Q

what is high-fructose corn syrup? (HFCS)

A

A sweetener manufactured in a multi step process from starch. It involves several immobilised enzymes which require different conditions

A level Biology Paper 1- Core concepts (5 decks)

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