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Cell Biology and Genetics > Enzymes > Flashcards

Enzymes Flashcards

1
Q

What is a chemical reaction?

A

Converting substrate into product
by breaking old bonds
forming new ones

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2
Q

What is activation energy?

A

Energy required to be put into the substrate in order to start it off

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3
Q

What is the transition state?

A

Point of maximum energy

have intermediate between substrate and product

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4
Q

How can the rate of a reaction be increased?

A

Increase temperature

Increase concentration

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5
Q

How does increasing temperature increase rate of reaction?

A

Molecules have more energy

more molecules with activation energy

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6
Q

How does increasing concentration increase rate of reaction?

A

More collisions between molecules

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7
Q

What are enzymes?

A

Biological catalysts

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8
Q

What do catalysts do?

A

Increase the rate of reaction

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9
Q

How do enzymes increase the rate of reaction?

A

Lower activation energy

Facilitate formation of transition state

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10
Q

How do enzymes lower the activation energy of chemical reactions?

A

Bring substrate molecules closer to each other
more likely to collide

Weaken the bonds in substrates
so less energy is required to break them

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11
Q

What is the active site of an enzyme?

A

Point where substrate binds

where the chemical reaction occurs

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12
Q

How much space of the enzyme does the active site take up?

A

Small amount

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13
Q

What is the function of the rest of the enzyme, other than the active site?

A

Act as a scaffold to form the active site

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14
Q

How are the amino acids that form the active site related to each other?

A

Active site is formed by amino acids at different points in the primary sequence
they come together by folding of the protein

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15
Q

What structure do most active sites form? Why?

A

Form clefts or crevices

to exclude water

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16
Q

How does the active site relate to the subtrate?

A

Active site has complementary shape to substrate

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17
Q

What is the lock and key hypothesis?

A

Substrate has completely complementary shape to active site

substrate fits into active site perfectly

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18
Q

What is the induced fit hypothesis?

A

Substrate has somewhat complementary shape to active site
binding of substrate to active site induces conformational change in active site
so that they fit together properly

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19
Q

How do substrates bind to active sites of enzymes? Why?

A

By multiple non-covalent bonds

binding must be weak

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20
Q

What are some examples of bonds that form between the substrate and active site?

A

Hydrogen bonds

Van der waals

Hydrophobic interactions

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21
Q

What shape would a graph of y axis-product against x axis-time look like? Describe the shape

A

Rectangular hyperbola

  • steep
  • flatter
  • completely flat
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22
Q

What does the gradient of a graph of y axis-product against x axis-time measure?

A

Measures the rate of reaction

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23
Q

Why does a graph of y axis-product against x axis-time take a hyperbolic shape?

A

Initially, lots of substrate molecules so have high rate of reaction

Then fewer substrate molecules, reduced rate of reaction

Then no substrate molecules, reaction stops

24
Q

Why does more substrate molecules means an increased rate of reaction?

A

More likely to collide with each other

form more product

25
Q

What is another term for rate of reaction? What is its symbol?

A

Reaction velocity, V

26
Q

What is V0?

A

The reaction velocity at time 0s

27
Q

How does temperature affect the rate of an enzyme-controlled reaction?

A

Initially, as temperature increases so does rate of reaction

but after optimum temperature, it decreases

28
Q

What is the optimum temperature?

A

Temperature that gives maximum enzyme activity and maximum rate of reaction

29
Q

Why does the rate of an enzyme-controlled reaction decrease after the optimum temperature?

A

Enzyme denatures with high temperatures

30
Q

What is enzyme denaturation?

A

Bonds in enzyme tertiary structure break
enzyme loses its tertiary structure
active site loses its 3D shape

31
Q

What are the consequences of the active site losing its shape?

A

Substrate can no longer bind

reaction stops

32
Q

How does pH affect the rate of an enzyme-controlled reaction?

A

Below or above optimum pH, rate of reaction decreases

33
Q

Why does the rate of an enzyme-controlled reaction decrease above or below the optimum pH?

A

Enzymes denatures

34
Q

What is the shape of a graph of y axis-reaction velocity against x axis-substrate concentration?

A

Rectangular hyperbola

35
Q

How does low or high pH cause enzyme denaturation?

A

Affects ionisation state on amino acids

affects electrostatic interactions in tertiary structure

36
Q

What is Vmax?

A

The maximum reaction velocity

37
Q

How is Vmax drawn on a graph?

A

Horizontal line above end point of graph

38
Q

What is happening with enzyme and substrate molecules at Vmax?

A

Enzyme active sites are saturated with substrate

cannot bind any more

39
Q

What is the Michaelis Menten model?

A

E + S E-S —–> P

40
Q

What is E-S?

A

Enzyme-substrate complex

is the intermediate between substrate and product

41
Q

What does the Michaeles Menten equation predict?

A

That the graph of y axis-reaction velocity against x axis-substrate concentration will be rectangular hyperbola

42
Q

What is Km?

A

Substrate concentration that gives half of Vmax

43
Q

What do Km values measure?

A

Affinity of enzyme for its substrate

44
Q

What does a low Km value mean? Why?

A

Enzyme has high affinitiy for substrate

because require lower concentration to reach Vmax/2

45
Q

What does a high Km value mean? Why?

A

Enzyme has low affinity for substrate

because require higher concentration to reach Vmax/2

46
Q

What do rates generally measure?

A

Amount per unit time

47
Q

How is enzyme activity measured?

A

Amount of enzyme that produces 1micromole of product per minute under standardised conditions

48
Q

How is measure of enzyme activity standardised?

A

Per litre

Per gram of tissue

49
Q

How does the rate of an enzyme-controlled reaction relate to enzyme concentration?

A

Rate of enzyme-controlled reaction is proportional to enzyme concentration

50
Q

How does enzyme concentration affect rate of reaction and enzyme activity?

A

Rate of reaction changes with enzyme concentration

Enzyme activity is not affected by enzyme concentration

51
Q

What is the Lineweaver-Burk plot?

A

Converting the rectangular hyperbola of y axis-reaction velocity against x axis-substrate concentration into a linear graph

52
Q

What are the x- and y-axes of the Lineweaver-burk plot?

A

x-axis is 1/substrate concentration

y-axis is 1/reaction velocity

53
Q

What is the advantage of the Lineweaver-burk plot over the rectangular hyperbola?

A

Can more easily measure Km and Vmax

54
Q

How is Km measured from a Lineweaver-burk plot?

A

x-intercept is -1/Km

55
Q

How is Vmax measured from a Lineweaver-burk plot?

A

y-intercept is 1/Vmax

56
Q

What is the gradient of the Lineweaver-burk plot?

A

Km/Vmax

Cell Biology and Genetics (32 decks)

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