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Z OLD Molecules, Genes and Disease > Enzyme Activity > Flashcards

Enzyme Activity Flashcards

1
Q

Give the general equation for a reversible reaction

A

Substrate ↔ products

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2
Q

What must be true if a reaction is going to occur?

A

There must be a change in energy

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3
Q

Why must there be a change in energy for a reaction to occur?

A

Because of the making and breaking of bonds

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4
Q

What is important for overcoming energy barriers?

A

Enzymes

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5
Q

Why are enzymes important for overcoming energy barriers?

A

They produce transition states

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6
Q

What is the transition state?

A

The high energy intermediate that lies between substrate and products

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7
Q

What is the activation energy?

A

The minimum energy that substrate must have to allow for the reaction

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8
Q

What must be done to increase the rate of reaction?

A

The energy barrier must be overcome

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9
Q

How can the rate of reaction be increased?

A
  • Temperature
  • Concentration
  • Enzymes
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10
Q

How does temperature increase rate of reaction?

A

It increases the number of molecules with the activation energy

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11
Q

How does concentration increase in the rate of reaction?

A

It increases the chance of molecular conditions

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12
Q

What are the limitations of changing the rate of reaction using temperature and concentration?

A

They can’t really be changed in biological systems

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13
Q

What are enzymes?

A

Biological catalysts that increase the rate of reaction by lowering the activation energy

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14
Q

What do enzymes facilitate?

A

The formation of the transition state

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15
Q

Why is rate of reaction important?

A

Because some reactions are very slow, so even if it’s a favourable reaction, it may not occur

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16
Q

What are the features of enzymes?

A
  • Highly specific

- Unchanged after reaction

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17
Q

What is the result of enzymes being highly specific?

A

They normally only work for 1 or 2 reactions

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18
Q

Do enzymes change at all?

A

They may be changed during the reaction

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19
Q

What do enzymes do to rate of reaction?

A

Increase it

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20
Q

What kind of molecules are enzymes?

A

Proteins (with one or two exceptions)

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21
Q

What may enzymes require?

A

Associated cofactors

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22
Q

What are cofactors?

A

Other things that allow enzymes to work

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23
Q

Why are enzymes relevant in medicine?

A
  • Inheritable genetic disorders can be caused by changes in an enzyme
  • Overactive enzymes can cause disease
  • Measurement of enzyme activity for diagnosis
  • Inhibition of enzymes for drugs
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24
Q

How can genetic disorders cause problems with enzymes?

A

Mutations can destroy or slow an enzyme

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25
Give an example of a disease caused by an overactive enzyme?
Some cancers
26
What is the active site?
The place where substrates bind, and where chemical reactions occur
27
How much of the enzyme does the active site occupy?
Only a small part; 5-6 amino acids
28
What is the purpose of the rest of the enzyme?
Acts as a scaffold for the active sit
29
What is the active site formed from?
Amino acids from different parts of the primary sequence
30
How is it possible that the active site amino acids come from different parts of the amino acid sequence?
When the protein is in it’s 3D confirmation, the amino acids are bought close together
31
Where do amino acids usually sit?
In clefts or crevices- not usually on the surface
32
What does the creft/crevice in which the active site usually do?
Excludes water
33
Why does the cleft/crevice the active site sits in usually exclude water?
Because water is so concentrated that it can interfere with the reaction
34
What shape is the active site?
One that is complementary to the substrate
35
What does the binding of the substrate to the active site induce?
A change in confirmation
36
What is the theory that the binding of substrate to the active site causes a change in confirmation called?
The induced fit hypothesis
37
When does the active site form a completely complementary shape to the substrate?
After the substrate has binds
38
What happens as the substrate binds?
The enzyme changes shape to accommodate the substrate
39
How is the substrate bound to the active site?
By multiple weak bonds
40
What type of bonds bind the active site to the substrate?
All non-covalent
41
Why must the binding of active site to substrate not be too tight?
Otherwise the product would not be released
42
What is the importance of the non-covalent interactions binding the substrate to the active site?
They hold it in exactly the right conformation
43
How do enzymes work?
By stabilising the transition state
44
What happens as the substrate levels decrease?
Product levels increase
45
What is V 0 ?
The initial rate of reaction
46
Why do we use V 0 ?
Because when measuring rate of reaction, we must know the concentration of the substrate, and the only time we know this is right at the start
47
What do different enzymes have?
Different optimum conditions
48
What do optimum conditions consist of?
#NAME?
49
What often happens as an enzyme catalysed reaction reaches maximum velocity?
The plot of reaction rate as a function of substrate concentration has the shape of a rectangular hyperbola
50
What does the Michaelis-Menten model for enzyme catalysis propose?
That a specific complex between enzyme and substrate is a necessary intermediate in catalysis
51
Give the chemical equation for the Michaelis-Menten model
E+S ↔ ES →  E+P
52
What is the Michaelis-Menten equation?
V 0  = Vmax[S] / Km + [S]  Where Km = Michaelis constant and V max  = maximal velocity (mol/min) Assuming an infinite [substrate]
53
What does the Michaelis-Menten equation predict?
A plot of V 0  versus [S] will be a rectangular hyperbola
54
What does the Michaelis-Menten equation tell us?
That rate is dependent on concentration
55
Do all enzymes obey the Michaelis-Menten model?
No
56
Which enzymes often don’t follow the Michaelis-Menten model?
Regulated enzymes that show co-operativity
57
What is Vmax?
The maximal rate when all enzymes active site are saturated with substrate
58
What does Vmax vary depending on?
Concentration of enzyme being measured
59
What is Km?
Substrate concentration that gives half maximal velocity
60
What do Km values give?
A measure of affinity of an enzyme to its substrate
61
What does a low Km mean?
High affinity for substrate
62
What does a high Km mean?
Low affinity for substrate
63
What is 1 unit?
The amount of enzyme that can catalyse 1 micromole of product per minute
64
What is the Lineweaver-Burk plot?
1/V 0 = Km/Vmax . 1/[S] + 1/Vmax
65
How can Km be determined from the Lineweaver-Burk plot?
It is the negative reciprocal of where the plot meets the x-axis
66
How can Vmax be determined from the Lineweaver-Burk plot?
It is the reciprocal of where the plot meets the y axis
67
What are enzyme inhibitors?
Molecules that slow down or prevent enzyme reactions
68
What do enzyme inhibitors include?
Many drugs
69
Are enzyme inhibitors reversible or irreversible?
Can be either
70
What happens when enzyme inhibitors are irreversible?
They bind very tightly, generally using a form of covalent bond, blocking function completely
71
What happens when enzyme inhibitors are irreversible?
They bind non-covalently and can free dissociate
72
What are the two types of enzyme inhibition?
#NAME?
73
Where do competitive inhibitors bind?
Active site
74
What must be true of a competitive inhibitor?
It must also be complementary to the active site
75
What does a competitive inhibitor reduce?
The proportion of enzyme molecules bound to substrate
76
Does a competitive inhibitor affect Km or Vmax?
Km
77
Why does a competitive inhibitor not affect Vmax?
Adding enough substrate will always overcome the effect of the inhibitor
78
Why does a competitive inhibitor increase Km?
Because the inhibitor competes with the substrate for active sites
79
Where does a non-competive inhibitor bind?
Another site of the enzyme
80
Does a non-competitive inhibitor affect Km or Vmax?
Vmax
81
What does a non-competitive inhibitor decrease?
The turnover number of an enzyme
82
How does a non-competive inhibitor exert its effect?
It changes the overall shape of the molecule
83
What other affect can compounds binding outside the active site have?
They can activate the enzyme, rather than inhibit

Z OLD Molecules, Genes and Disease (14 decks)

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