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Foundations of Medicine > Enzymes > Flashcards

Enzymes Flashcards

1
Q

What is an enzyme?

A

A protein molecule that catalyzes chemical reactions without itself being destroyed or altered

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2
Q

What are enzymes involved in?

A

Almost every biochemical reaction

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3
Q

Define substrate

A

A reactant in catalysed reaction

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4
Q

Define active site

A

The part of the enzyme that binds the substrate to form the enzyme-substrate complex

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5
Q

Define product

A

The substance produced by the enzyme-catalysed conversion of a substrate

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6
Q

Define cofactor

A

Non-enzyme component needed for the reaction (eg magneciusm)

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7
Q

Define isoenzyme

A

Enzymes that catalyse the same reaction but vary in structure and other biochemical properties

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8
Q

What is the activation energy?

A

Energy needed for the reaction to proceed

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9
Q

How do molecules in free solution react?

A

By bumping into each other

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10
Q

How do enzymes increase the rate of reaction?

A

Lower the activation energy

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11
Q

Define riboenzyme

A

Catalytic RNA molecules with no protein compact

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12
Q

What is a prosthetic group?

A

A non-protein group forming part of or combined with a protein.

i.e - A cofactor covalently bound to an enzyme or very tightly associated with an enzyme

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13
Q

What is an apoenzyme?

A

An inactive enzyme.

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14
Q

When does enzyme activation occur?

A

Upon binding of an organic or inorganic cofactor

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15
Q

How do enzymes lower the activation energy?

A

Entropy reduction
Desolvation
Induced fit

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16
Q

How does entropy reduction lower the activation energy?

A

Enzymes “force” the substrates to be correctly orientated by binding them in the formation they need to be in for the reaction to proceed

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17
Q

How does desolvation lower the activation energy?

A

Weak bonds between the substrate and enzyme essentially replace most of all of the H-bonds between substrate and aqueous solution

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18
Q

How does induced fit lower the activation energy?

A

Conformational change occur in the protein structure when the substrate binds

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19
Q

Define Michaelis constant

A

The Michaelis constant (KM), defined as the concentration of substrate that is transported at half the maximal velocity (Vmax) of transport, is a measure of the affinity of the transporter for its substrate.

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20
Q

Define the following in regards to Michaelis-Menton Constant:

V
V0
Vmax
[S]
Km

A

V = velocity aka rate

V0= initial reaction velocity

Vmax= maximum reaction velocity

[S] = substrate concentration

Km= the substrate concentration wen the reaction is at half the maximum velocity (Vmax)

21
Q

What does Km tell us?

A

Km - how specific the enzyme is for the substrate

  • Low value - good fit
  • High value - poor fir i.e. takes a lot of substrate to get to half Vmax
22
Q

What does Vmax tell us?

A

Vmax - how fast a reaction is proceeding when the enzyme is saturated with substrate

23
Q

What are factors that affect enzyme reactions?

A

Enzyme concentration
Substrate concentration
Temperature
pH
Inhibitors

24
Q

How does enzyme concentration affect enzyme reactions?

A

The higher the enzyme concentration, the more enzymes there are to form enzyme-substrate complexes, leading to an increase in enzyme activity.

This happens up to a certain point.

Enzyme activity then levels off (plateaus) as there are not enough substrate molecules to react with the extra enzymes.

25
Q

How does substrate concentration affect enzyme reactions?

A

Enzymes will work best if there is plenty of substrate.

As the concentration of the substrate increases, so does the rate of enzyme activity.

However, the rate of enzyme activity does not increase forever.

This is because a point will be reached when the enzymes become saturated and no more substrates can fit at any one time even though there is plenty of substrate available.

26
Q

How does temperature affect enzyme reactions?

A

As the temperature rises, the number of collisions between the enzymes and substrate speed up, increasing the rate of the reaction.

However it’s important to remember the enzymes themselves are actually proteins and each enzyme will have an optimal temperature mph that it can work can’t.

27
Q

How does pH affect enzyme reactions?

A

Deviating from the optimum pH (too high or too low) causes the enzyme’s active site to become denatured and the active site loses its important shape.

28
Q

How do inhibitors affect enzyme reactions?

A

Inhibitors are molecules that partially fit into an enzyme’s active site but are not broken down.

They inhibit the reaction.As long as they are in the active site the substrate cannot enter to be broken down, thus reducing the rate of reaction.

There are two types of inhibitors - competitive and non-competitive

29
Q

What are competitive inhibitors?

A

Competitive inhibitors are molecules with a similar structural shape to the normal substrate of the enzyme and so can fit into its active site.

They compete with a substrate molecules for a position in the active site on the enzyme.

30
Q

What are non-competitive inhibitors?

A

This occurs when an inhibitor does not bind to the active site but does bind to a different part of the enzyme and changes the active site shape.

This stops the substrate binding to the enzyme and decreases the reaction rate.

31
Q

What happens to the rate of a reaction with competitive inhibitors?

A

With some of the active sites occupied and blocked by the inhibitor the rate of reaction is reduced however if the substrate concentration is increased, the chance of the substrate binding to the enzyme is increased and the rate of the reaction can return to normal.

32
Q

What happens to Vmax and Km in competitive inhibition?

A
  • Vmax unchanged
  • Km increases because it takes more substrate to overcome the inhibition
33
Q

What happens to Vmax and Km in non-competitive inhibition?

A
  • Vmax decreased
  • Km remains the same
34
Q

Why is it important to measure enzymes in clinical settings?

A
  • Detection of suspected disease at pre-clinical stage
  • Confirmation of suspected disease and assessing severity
  • Localisation of disease to organs
  • Assessing the response to therapy
  • Organ function assessment
  • Detection of inherited metabolic disease
  • Detection of vitamin deficiencies
35
Q

What factors can influence enzyme activity in samples?

A
  • Age
  • Gender
  • Pregnancy
  • Race
  • Time of day
  • Genetics
  • Drugs
  • Disease process, progress and treatment e.g surgery
36
Q

When do serum concentrations usually rise?

A

Although there are some enzymes that are secreted from cells, generally serum concentrations are low and rise only when there is damage to cells and release of contents

37
Q

What can the release of enzymes trigger?

A

Hypoxia
Cellular damage
Physical damage
Immune disorders
Microbiological agents
Genetic defects
Nutritional disorders

38
Q

What is proportional to the amount of the enzyme present?

A

Rate of an enzyme-catalysed reaction is directly proportional to the amount of the enzyme present

39
Q

What is monitored when using enzymes in the lab?

A

Progress of conversion of the substrate to product is monitored

40
Q

What are the problems with enzyme measurement?

A

Not specific - i.e can be found in more than one tissue in the body

Particular requirements - temperature, pH etc

Assays must be optimised

41
Q

What is an assay?

A

An analysis done to determine the presence of a substance and the amount of that substance

42
Q

Why isn’t a spontaneous reaction instaneous?

A

Because of the activation energy barrier

43
Q

What is the activation energy used for?

A

Positioning chemical groups correctly

44
Q

What is the transition state?

A

The moment that chemical bonds are formed and broken The reaction from this point could then go to products or reactants

45
Q

What type of bond occur between substrate and enzyme?

A

Non-covalent

46
Q

What is the active site complementary to?

A

The transition stage

47
Q

Which part of an enzyme reaction occurs more slowly?

A

The second part of the equation, producing E and P from the enzyme substrate complex

48
Q

Which stage of an enzyme reaction is reversible?

A

The formation of ES from E and S K1 denotes the forward reaction K-1 denotes the reverse reaction

Foundations of Medicine (56 decks)

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