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UCLMS Yr 1 Mod 1: Foundations of Health and Medical Practice > Enzymes > Flashcards

Enzymes Flashcards

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USMLE® Step 1 flashcards
1
Q

What are cofactors

A

Additional components to aid catalytic activity

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2
Q

What are the three types of Co-factors

A

Metals, Prosthetic groups and co-enzymes

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3
Q

Which type of reaction is catalysed by Oxidoreductases

A

Redox Reactions

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4
Q

Which type of reaction is catalysed by Transferases

A

Group Transfer Reactions

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5
Q

Which type of reaction is catalysed by Hydrolases

A

Hydrolysis reactions

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6
Q

Which type of reaction is catalysed by Lyases

A

Addition/removal of groups to form double bonds

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7
Q

Which type of reaction is catalysed by Isomerases

A

Isomerisation Reactions

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8
Q

Which type of reaction is catalysed by Ligases

A

Ligation reactions of two substrates at the expense of ATP hydrolysis

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9
Q

Can Enzymes effect equilibrium

A

No, they help to reach equilibrium faster

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10
Q

What 4 parameters affect enzyme activity

A

pH
Temperature
Enzyme concentration
substrate concentration

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11
Q

How does pH affect enzyme activity

A

Affects in particular ionisable amino acids
Alters the structure of the active site
Affects catalytic ability or substrate binding ability

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12
Q

How does Temperature effect enzyme activity

A

Increases the rate of enzyme-catalysed reactions
the interactions that determine the 3D shape of the enzyme become disrupted with further increases in temperature
The longer the incubation time, the more noticeable the effects

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13
Q

What can impact Thermolability

A

Mutations that can disrupt the stability in the expected temperature range (denature faster than expected)

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14
Q

How does enzyme concentration impact enzyme activity

A

increasing the concentration of the enzyme increases its activity
This is until the substrate becomes limiting

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15
Q

What is the Vmax of an enzyme

A

The fastest theoretical speed the enzyme can work at

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16
Q

What is the Kcat of an enzyme

A

How many reactions an enzyme can catalyse per unit time (specific to an enzyme)

17
Q

What is the formula to calculate Kcat

A

Kcat = Vmax/[E]

18
Q

What is the Km of an enzyme

A

the amount of substrate required to reach 1/2Vmax

19
Q

What is the Km used for

A

The substrate concentration that most sensitively affects enzyme activity

20
Q

What does lipoprotein lipase do

A

Releases fatty acids from circulating lipoproteins so that the free fatty acids can be taken up by surrounding tissues
Released by both adipose tissue and skeletal muscle

21
Q

Why does adipose tissues LPL have a high Km

A

The rate of FA release is dependent on LPL protein levels
After a meal, LPL levels are high
Adipose LPL are highly active, and the free fatty acids released can be stored in the adipose tissue

22
Q

Why does skeletal muscle LPL have a low Km

A

The rate of FA releases is dependent on the [LPL] as the enzyme is saturated at low LPL levels
After a meal, activity does not increase any further, as the enzyme is saturated
Between meals, the amount of free fatty acids released from LPL id dependant on how much LPL is secreted by the muscle

23
Q

What is co-operativity

A

When the substrate also binds to another active site on the enzyme, affecting activity

24
Q

What is negative co-operativity

A

Increased substrate concentration inhibits the activity of the enzyme

25
Q

What is positive co-operativity

A

When increased substrate activity increases the activity of the enzyme

26
Q

What is Irreversible inhibition

A

Permanently modifies the enzyme, often covalently
Km unaltered
Vmax decreases

27
Q

What are reversible inhibitors

A

Inhibitors bind to the enzyme or enzyme complexes via hydrophobic, ionic or van Der Waals intreactions

28
Q

What are competitive inhibitors

A

Compete with the substrate for the active site of the enzyme
normally have a similar structure
make it more difficult for the actual substrate to bind to the active site
The activity of the enzyme remains unchanged, so the Vmax does not change
more substrate required to achieve results, so the Km increases

29
Q

How do you overcome competitive inhibitors

A

Increase the concentration of substrate

30
Q

What are statins

A

used to lower the cholesterol in the blood, in order to prevent CVD

31
Q

How much do statins decrease plasma [LDL]

A

30-60%

32
Q

What are uncompetitive inhibitors

A

the binding of the substrate results in the a binding of the inhibitor, forming an unproductive ESI complex
This draws the E/ES equilibrium towards ES.
Lower Km
Lower Vmax

33
Q

What concentration are uncompetitive inhibitors more effective

A

high substrate concentrations

34
Q

What are non-competitive inhibitors

A 
Inhibitor can bind to either E or ES
doesn't alter binding
prevents catalysis
Decreases the concentration of functional enzyme
Vmax decreases
Km unaffected
35
Q

What are protein kinase inhibitors

A

Typically ATP competitive inhibitors with low specificity but a high affinity

UCLMS Yr 1 Mod 1: Foundations of Health and Medical Practice (6 decks)

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