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PSA712 Biochemistry > Enzymes > Flashcards

Enzymes Flashcards

1
Q

Define what an enzyme is.

A

Enzymes are biological catalysts that speed up the RoR, without themselves being changed in the process.

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2
Q

List 3 processes in the body where enzymes can be used.

A
  1. Metabolism (converting food to energy).
  2. Movement (muscle contraction).
  3. Digestion
  4. Cell Signalling (e.g. Hexokinase adds phosphate to glucose).
  5. Gene Expression
  6. Biosynthesis
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3
Q

Mutations resulting in under/over production in a single critical enzyme can lead to what?

A

Disease.

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4
Q

What is Phenylketonuria (PKU)?

A

PKU is a genetic disorder in which phenylalanine hydroxylase mutates.
This leads to a reduced metabolism of phenylalanine.

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5
Q

A toxic build up in the blood or brain can cause what? List two outcomes.

A
  1. Microcephaly (small undeveloped head).
  2. Intellectual disability.
  3. Siezures.
  4. Behavioural problems.
  5. Eczema.
  6. Musty odour.
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6
Q

Enzymes are globular proteins. The active site consists of two specific structures, what are these?

A
  1. Binding site - binds and orients substrate.

2. Catalytic site - reduces chemical activation energy.

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7
Q

Enzymes can increase reaction rates by how many folds?

A

10^17 folds.

1000 quadrillion folds

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8
Q

The non-polar environment of the enzyme’s active site helps to do what?

A

Enhance binding by multiple weak forces.

e.g. hydrogen, Van der Waals, electrostatic

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9
Q

The induced fit model suggests there is a change upon binding - what is this change?

A

Substrate binding to active site induces a conformational change.

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10
Q

What determines substrate specificity?

A

The amino acid sequence (primary structure) of the enzyme.

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11
Q

TRUE OR FALSE:

The allosteric site and active site are the same thing.

A

FALSE - the allosteric site is distinct from the active site.

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12
Q

When a substrate binds to an allosteric site, this causes a conformational change. What could this lead to?

A

Change in the active site.
Activation or inhibition of reactions.
Increase or decrease in RoR.

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13
Q

Some enzymes require co-factors for optimal activity. List one inorganic cofactor and one organic.

A
  1. Inorganic = metal ions.

2. Organic = heme, folic acid, NAD+.

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14
Q

In what way is the binding of co-enzymes different to that of normal binding.

A

Co-enzymes are only transiently bound, meaning there is only a temporary interaction.

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15
Q

Name one co-enzyme deficiency and state two things in which it leads to.

A

Scurvy.

Leads to: lethargy, bleeding gums, poor wound healing, jaundice, neuropathy, death due to infection.

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16
Q

Prothetic groups, such as co-factors, are bound to the enzyme in what way?

A

Covalently bonded.

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17
Q

What is the function of oxidoreductases?

A

Transfer hydrogen/oxygen/electrons from one substrate to another.

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18
Q

What is the function of transferases?

A

Transfer functional groups from one substrate to another.

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19
Q

What is the function of hydrolases?

A

Hydrolyse a substrate.

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20
Q

What is the function of lyases?

A

Add/remove a group in order to form a double bond.

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21
Q

What is the function of isomerases?

A

Transfer groups within molecules.

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22
Q

What is the function of ligases?

A

Formation of bonds, coupled with ATP hydrolysis.

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23
Q

An example of a lysozyme if glycosidehydroase. It acts as a natural antibacterial defence. What are the 2 types of bacteria it protects us from?

A
  1. Gram positive - has a peptidoglycan wall and can take up the ‘gram’ stain.
  2. Gram negative - has a thinner peptidoglycan wall coated with an outer membrane and cannot take up the ‘gram’ stain.
24
Q

Product formation levels off with time and remains constant. This is known as what?

A

Equilibrium

25
Q

Enzyme Accelerate Reaction Rate can be displayed in what formula.
Use S, +E and P.

A

S (+E) = P

26
Q

State the 1st Law of Thermodynamics.

A

The total energy of a system is constant - energy cannot be created/destroyed, only converted.

27
Q

When an enzyme is in transition state, it means what?

A

The substrate is no longer in tact, but the products haven’t yet been formed (AKA ES complex).

28
Q

List 3 ways in which enzymes reduce activation energy.

A
  1. Binding
  2. Spatial complementarity (close the molecules, the more likely they are to bind)
  3. Induced fit
  4. Chemical complementarity
  5. Specific AA R-groups
29
Q

What factors determine whether a substrate and enzyme successfully bind (enzyme catalysis)?

A
  1. Microenvironment (environment in active site)
  2. Orientation
  3. Hydrophobic interactions
  4. Bonds (hydrogen, disulphide, Van der Waals)
30
Q

What are the 4 catalytic mechanisms?

A
  1. Approximation - closer substrates are more likely to bind.
  2. Metal ion - better ions will increase RoR.
  3. Covalent - enzyme and substrates share covalent bonds.
  4. Acid base - side chains have different charges.
31
Q

What is V0 in literal terms?

A

The rate of reaction where it is the fastest.

32
Q

Measuring V0 minimises other complicating factors. How?

A

The reaction is at its:

  1. Fastest rate
  2. Highest substrate conc
  3. Least amount of products
  4. Least amount of feedback inhibition - minimises the risk of products being inhibiting factors
33
Q

What is the relationship between [S] and V0?

A

Doubling [S], doubles V0.

34
Q

When enzymes are fully saturated, what will happen to the rates of V0.

A

No increase, will remain constant.

35
Q

When a plateu occurs on a product time graph, what does this indicate?

A

There is more substrate available than active sites, enzymes become the limiting factor as all active sites are saturated.

36
Q

What is Michaelis constant (Km)?

A

The concentration of substrate needed to reach half Vmax.

37
Q

Why do enzymes have different Michaelis constants?

A

Based on affinity to substrates.

38
Q

A high Michaelis constant indicates what?

Refer to binding, affinity and RoR.

A
  1. Weak binding
  2. Low affinity
  3. Slow RoR
39
Q

A low Michaelis constant indicates what?

Refer to binding, affinity and RoR.

A
  1. Strong binding
  2. High affinity
  3. Fast RoR
40
Q

What affect does temperature have on enzymes? State the positive and negative affects.

A
  1. Increase in thermal energy overcomes activation energy - leads to an increase in RoR.
  2. Beyond optimum, bonds break, alters activation site, protein denatures.
41
Q

What affect does pH have on enzymes?

A

Small deviations from the optimum pH will result in a decrease in enzyme activity.

42
Q

Enzyme assays monitor the disappearance of substrate or appearance of products. In what way can this be measured?

A
  1. Change in colour
  2. Change in light absorbance
  3. Chromatography
  4. Radiography
43
Q

Competitive inhibitors have a similar structure to substrates. How do they function?

A

Competitive inhibitors bind to the enzyme’s active site and block the substrate from binding. Products cannot be formed.

44
Q

Reversible inhibitors bind to enzymes via weak non-covalent bonds. What makes them reversible?

A

They do not chemically change the enzyme.

45
Q

List three reversible types of specific inhibitors.

A
  1. Competitive
  2. Non-competitive
  3. Uncompetitive
46
Q

How can the use of [S] overcome the activity of competitive inhibitors?

A

Increasing the [S] means there is more substrate to bind to active sites than inhibitors.

47
Q

When competitive inhibitors are present, what happens to Vmax and Km?

A

Vmax remains unchanged.

Km increases - RoR is reduced and affinity of enzyme for substrate is reduced.

48
Q

A non-competitive inhibitor binds to what site?

A

Allosteric

49
Q

When non-competitive inhibitors are present, what happens to the Vmax and Km?

A

Vmax is reduced.

Km does not change.

50
Q

Uncompetitive inhibitors bind to what?

A

The ES complex.

51
Q

When uncompetitive inhibitors are present, what happens to Vmax and Km?

A

Vmax decreases.

Km is lowered and there is a higher affinity for substrate at the start of the reaction.

52
Q

Allosteric enzymes are usually multi-subunit. What does this mean?

A

Enzymes have an active site on each subunit = oligomeric.

53
Q

Allosteric enzymes are usually present when cooperativity is important (e.g. oxygen dissociation). Describe what this means.

A

Binding substrate to one active site causes a conformational change and increases affinity of other active sites for substrate.

54
Q

Allosteric enzyme function can be displayed as a what curve on graphs?

A

Sigmoidal curve.

55
Q

List 2 other methods of enzyme/substrate regulation.

A
  1. Reversible covalent modification

2. Proteolytic activation - hydrolysis or apoptosis of cell.

56
Q

Gene expression regulates enzyme synthesis. Enzymes have short lived mRNA what does this help to do?

A

Control rate of protein expression.

PSA712 Biochemistry (11 decks)

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