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PMP101 > Enzymes & Catalysis > Flashcards

Enzymes & Catalysis Flashcards

1
Q

What are Enzymes?

A

Biological Catalysts that speed up specific enzymatic reactions
They are proteins (not RNAa ribozymes)

-They are present in all organisms
-Every chemical reaction of human cell is regulated by Enzymes
-There can be simple enzymes and multifunctional enzymes
-Their catalytic activity depends on integrity of the native protein folding

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2
Q

What are simple Enzymes?

A

Enzymes of which are single polypeptide chains

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3
Q

What are allosteric and multifunctional enzymes?

A

Enzymes of which have other complexes of more subunits

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4
Q

What does the catalytic activity of an enzyme depend on?

A

The integrity of their native protein folding

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5
Q

What is native protein folding?

A
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6
Q

What happens if enzymes are denatured or dissociated into subunits?

A

Catalytic activity is lost

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7
Q

How can an enzyme become denatured? What is it?

A
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8
Q

What are the properties of Enzymes?

A

-Specific for the substrates (reactants)
-Catalytic power, fast
-Efficient and not altered after the reaction
-Can be regulated

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9
Q

What is enzyme specificity? and Substrate specificity?

A
  • Ability of the enzymes to specifically recognise the proper substrate (reactant). It is a molecular recognition mechanism. Recognition and specificity is based on structural complementary (three-dimensional fit)
  • Substrates bind to a specific region of the enzyme called the active site
  • Enzyme-substrate complex (ES) formation is the first step in enzymatic catalysis
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10
Q

What Is the equation for Enzyme-substrate complex?

A
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11
Q

Substarte Specificity- Lock and key Model-Induced fit

A
  • The active site and substrate are perfectly complementary for each other (like a key fits into its respective lock)
  • Induced fit- The substrate is not exactly complementary to the active site. When it binds to the enzyme, a conformational change occurs to allow a better fit between the active site and substrate (like a hand in a glove)
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12
Q

What is the Active Site ?

A

A 3D pocket/groove, located in a small region of the enzyme

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13
Q

What is the active site composed of?

A

-Substrate binding site
-Catalytic Site

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14
Q

What is the Substrate binding site?

A

Amino acids side chains interact with the substrate primarily through hydrogen bonding and other electrostatic interactions. These interactions orientate the substrate within the active site.

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15
Q

What is the Catalytic Site?

A

Amino acids that catalyse the reaction. The correct folding of the enzymes is required. Substrate-enzyme binding alters the structure of the substrate to promote the formation of the transition state.

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16
Q

What is Catalytic Power?

A
  • Increase the rate of a chemical reaction. Most reactions are at least a million/billion times faster (106 to up to 1017 times) in the presence of an enzyme.
  • Orotidine monophosphate (OMP) decarboxylase catalyses reactions in milliseconds that could take 78 million years without an enzyme (1017 times faster)
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17
Q

To start any chemical reaction, what is required?

A

Energy

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18
Q

The minimum amount of energy required to start a reaction is known as?

A

ACTIVATION ENERGY

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19
Q

What is Activation Energy?

A

The energy that must be added to cause molecules to react with each other
-Reactions with a low activation energy will proceed as a faster rate

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20
Q

What happens to reactions with a low activation energy?

A

The will proceed at a faster rate

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21
Q

What is Enzyme Catalytic Power?-Diagram

A
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22
Q

Enzyme properties -Efficiency and Reusability

A
  • Enzymes remain unaffected by the reaction which they catalyse
  • Not altered or consumed during or after the reaction
  • Reusable -they can continue to work if they have more substracts
  • They are extremely efficient
  • They are active at very low concentrations
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23
Q

Enzyme Properties - Enzymatic Modulation

A
  • Various conditions affect enzyme function (reaction rate)
  • Temperature
  • Ionic conditions
  • pH
  • Substrate concentration
  • Presence of inhibitors
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24
Q

Enzymes work more efficiently at an…

A

Optimum temperature of 37 degrees in humans
Higher in some Archea

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25
Q

Do enzymes work at lower temperatures? and temperatures that are too high?

A
  • Show little activity at lower temperatures. Molecules have low kinetic energy
  • They can lose activity at high temperature as denaturation occurs (loss of native folding) and the active site no longer matches with the substrate. Loss of catalytic activity occurs.
26
Q

What is enzyme denaturation?

A
27
Q

pH and enzymatic activity

A
  • Enzymes are most active at an optimum pH

-about pH 7.5 for enzymes in the small intestine

-about pH 1.5 for stomach enzymes (Pepsine)

-about pH 4-5 for digestive lysosomal enzymes

  • Contain R groups of amino acids with proper charges at optimum pH
  • Lose activity in low or high pH as the tertiary structure is disrupted
28
Q

Does substrate concentration have an effect of Enzyme activity? diagram

A
  • At a constant concentration of enzyme, an increase in substrate concentration will cause an increase in the enzyme activity up to the point where the enzyme becomes saturated with the substrate
  • When an enzyme is saturated, it has reached its maximum activity (steady state) and maximum the rate of reaction (Vmax)
  • At a steady state, increasing substrate concentration will not change the reaction rate. The reaction rate depends only on how rapidly the enzyme can process the substrate.
29
Q

What is Kinetics?

A

The study of reaction rates

30
Q

From Michaelis-Menten equation for Kinetics :

A

Km=the concentration of substrate at which the reaction rate is half-maximal.

Km is an inverse measure of how tightly the enzyme binds its substrate

  • The higher the Km, the weaker the binding. The enzyme requires a greater concentration of substrate to achieve Vmax.
  • The lower the Km, the stronger the binding
31
Q

What are enzyme inhibitors ?

A
32
Q

What are the two types of Enzyme inhibitors?

A

-Competitive
-Non-competitive

33
Q

What are competitive inhibitors? diagram

A
  • Flu antiviral drug Oseltamivir (Relenza). Its structure closely mimics the natural substrate of the influenza virus enzyme, neuraminidase.
  • Competing with the substrate by binding the active site and blocking it. The effect can be reversible or irreversible (Covalent bonds)
34
Q

What are non-competitive inhibitors?

A
  • Anti-HIV drug Efavirenz (EFV). It inhibits the HIV-1 reverse transcriptase enzyme, in a non-competitive manner.
  • They bind to a site (allosteric) on the enzyme, which is not the active site. This causes a conformational change in the enzyme and the block of the catalytic activity. Their effect is usually reversible.
35
Q

What are Enzyme Cofactors? diagram

A

Some enzymes do not require additional chemical groups for activity. Others require cofactors (additional chemical components). Their catalytic activity depends on cofactors, as they provide active site reactive groups.

36
Q

Enzyme Cofactors-What are the Essential Ion cofactors?

A

-Activator Ions
-Metal ions

37
Q

What are activator ions?

A

Reversibly bind to the enzyme and often participate in substrate binding

38
Q

What are metal ions? diagram

A

Cations that are tightly bound to enzyme and participate directly in catalysis

39
Q

What are Co-substrates ?

A
  • Weakly/temporarily bound to an enzyme
  • Altered during the course of the reaction and dissociate from the active site (regenerated in another enzymic reaction and recycled)
  • Nicotinamide adenine dinucleotide (NAD+)
  • Nicotinamide adenine dinucleotide phosphate ( NADP +)
40
Q

What are Prosthetic Groups?

A
  • Tightly bound to the enzyme or even attached through a covalent bond
  • Must be regenerated each catalytic cycle

-Haem (in haemoglobin), for oxygen binding and redox reactions

-Biotin or vitamin B7-for carboxylase enzymes

-FAD, for redox reactions

41
Q

What are redox reactions?

A
42
Q

What is a Holoenzyme?

A

A complete catalytically-active enzyme together with its cofactor

43
Q

What is an Aponenzyme?

A

The protein part of the enzyme on its own without its cofactor is called an apoenzyme (not active)

44
Q

What is Enzyme nomenclature?

A
45
Q

he international Union of Biochemistry categories enzymes into 7 major groups: What are they?

A

1) Oxidoreductase

2) Transferases

3) Hydrolases

4) Lyases

5) Isomerases

6) Ligases

7) Translocases

46
Q

The ‘Enzyme Commission’ assigns what to each enzyme type?

A

a unique code number to each enzyme

For example: Diagram

47
Q

What is Enzyme Class 1 : Oxidoreductases

A

Catalyse oxidation and reduction (REDOX) reactions include dehydrogenases, oxidases, peroxidases, reductases

48
Q

What is Enzyme Class 2- Tranferases

A

Catalyse functional group transfer reactions includes kinases, family of enzymes that catalyse phosphorylation reactions

49
Q

What is Enzyme Class 3-Hydrolases

A
  • Catalyse hydrolysis reactions (transfer functional groups to water, by breaking of a bond) Includes esterases that cleave ester bonds in lipids, and phosphatases cleaving phosphate groups of molecules, proteases that cleave the peptide bonds of proteins.
  • All the lysosomal enzymes are acid hydrolases (different substrates)
50
Q

What is Enzyme Class 4- Lyases

A

Catalyse the cleavage of C-C,C-O,C-N, or other bonds by elimination, leaving double bonds or rings, or addition of groups to double bonds. It means, they catalyse the breaking of a chemical bond between two parts of a molecule (other than hydrolytic or oxidative bond breaking)

51
Q

What is Enzyme Class 5-Isomerases

A

Catalyse transfer groups within molecules to yield isomeric forms.

52
Q

What is Enzyme Class 6-Ligases

A

The joining (ligation) of two large molecules by forming a new chemical bond with the release of energy.

53
Q

What is Enzyme Class 7-Translocases

A

Movement of molecules or ions across membranes or their separation within membrane.

54
Q

What is the rule for every type of enzyme?

A

They are not altered during enzymatic reactions

55
Q

What are Enzymes - Main points

A

Enzymes are biological catalysts that speed up the rate of specific reactions by lowering the activation energy required to proceed. The lower the activation energy, the faster the rate of reaction.

56
Q

Enzymes are highly what?

A

Specific, efficient and reusable

57
Q

What is the functional part of an enzyme?

A

The active site which posses the binding site to interact with the substrate (the reactant) and the catalytic activity to carry out its specific reaction

58
Q

What is the enzyme interaction specific to?

A

The interaction with the substrate is specific, based on structural complementarity (2 models described)

59
Q

Factors such as what can affect the activity of an enzyme?

A

Factors such as pH, temperature, substrate concentration, and the presence of inhibitors can affect the activity of an enzyme.

60
Q

What is the name of an activated enzyme linked to its cofactor ?

A

Holoenzyme

61
Q

Which following features are common to every enzyme?

A

Enzymes are not altered during enzymatic reactions

PMP101 (23 decks)

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