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Molecules, Genes and Diseases > Lecture 7.1: Enzymes > Flashcards

Lecture 7.1: Enzymes Flashcards

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Organic Chemistry 101 flashcards
1
Q

What is rate of reaction influenced by? (4)

A

• Concentration of reactants
• Activation energy
• Temperature
• Presence of a catalyst

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2
Q

Activation Energy

A

For a reaction to occur, the reactants must acquire enough energy to enable
them to react with each other

This energy comes from e.g. reactants colliding with each other

The greater the activation energy, the slower the rate of reaction

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3
Q

Catalysts

A

They reduce Ea needed for a reaction to occur

They may bring reactants closer together and in an appropriate orientation for the reaction to proceed

A compound that speeds up a chemical reaction without itself undergoing any permanent change, so is free to be used again

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4
Q

What is an enzyme?

A

It is a biological catalyst – made from proteins each has a unique amino
acid composition each has a unique 3D structure

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5
Q

Mechanisms of Enzyme Action? (2)

A

1) Lock and key
2) Induced fit

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6
Q

Why are enzymes selective?

A

Because they have unique 3D structures

This means they display selectivity for the reactions they catalyse

The substrate(s) they work with must fit the active site (analogous to ligand bind region on receptors)

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7
Q

Absolute Enzymes

A

Only catalyse one specific reaction

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8
Q

Group Enzymes

A

Only act on molecules with a specific functional group (e.g. methyl groups)

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9
Q

Linkage Enzymes

A

Will only act on a specific type of chemical bond (e.g. peptide bonds)

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10
Q

Stereochemical Enzymes

A

Will only act on a particular optical isomer of a molecule

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11
Q

Classification of Enzymes (6)

A

Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases

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12
Q

Oxidoreductases Reaction Type

A

Oxidation-Reduction

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13
Q

Transferases Reaction Type

A

Transfer of groups e.g. amino, carboxyl between molecules

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14
Q

Hydrolases Reaction Type

A

Cleave bonds coupled with the insertion of water

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15
Q

Lyases Reaction Type

A

Cleavage of C-C, C-S and C-N bonds

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16
Q

Isomerases Reaction Type

A

Bond rearrangement

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17
Q

Ligases Reaction Type

A

Bond formation between C-O, C-N and C-S

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18
Q

What can rate of enzyme catalysed reactions can be influenced by? (7)

A

Substrate concentration

Enzyme concentration (in real life, [S] are generally&raquo_space; [E])

Enzyme activity (influence of other factors e.g. allosteric modulators that may alter properties of the active site e.g. increasing affinity for substrate)

pH
Temperature
Presence of ions
Presence of inhibitors

19
Q

The significance of Km values: low Km and high Km

A

Km values represent affinity of an enzyme for its substrate

Low Km = high affinity for substrate
High Km = low affinity for substrate

20
Q

What is 1 unit on a Vmax/V0 graph

A

1 unit = the amount of enzyme that converts 1micromol of product per min under standard conditions

21
Q

What is the standardised rate?

A

Per litre (L) of serum or per gram (g) of tissue

22
Q

Enzyme Inhibitor Types (2 + 2 sub)

A

Irreversible
Reversible [Competitive and Non-Competitive]

23
Q

Irreversible Enzyme Inhibitor

A

Bind very tightly, generally form covalent bond(s)

Examples: nerve gases, sarin blocks acetylcholine esterase

24
Q

Competitive Enzyme Inhibitor

A

Binds at active site

Affects Km, not Vmax

25
Q

Non-Competitive Enzyme Inhibitor

A

Binds at another site on the enzyme

Affects Vmax but not Km

26
Q

What is Km?

A

The concentration of substrate which permits the enzyme to achieve half Vmax

27
Q

What is Vmax?

A

The reaction rate when the enzyme is fully saturated by substrate

28
Q

Competitive Inhibition Mechanism

A

• Resembles the substrate
• Binds to the active site
• Reduces the proportion of enzyme molecules
bound to the substrate

29
Q

Non-Competitive Inhibition Mechanism

A

• Binds at an alternative site on enzyme (allosteric
site)
• Alters the shape of the molecule (enzyme)
• Decreases the turnover number of the enzyme→
lowering Vmax

30
Q

What is the Turnover Number?

A

The turnover number is the number of substrate molecules transformed per minute by a single enzyme molecule

31
Q

Long Term Regulation of Enzyme Activity

A

Change in rate of protein synthesis
• Enzyme induction/repression
• Through a change in transcription/translation

Change in rate of protein degradation
• Ubiquitin-proteasome pathway

32
Q

Short Term Regulation of Enzyme Activity (seconds to hours)

A

Substrate and product concentration

Change in enzyme conformation:
• Allosteric regulation
• Covalent modification
• Proteolytic cleavage (irreversible)

33
Q

Feedback Inhibition

A

The end product of a metabolic pathway has the ability to inhibit a enzymatic step upstream

34
Q

Allosteric Enzymes

A

• Distinct regulatory sites
• Regulation by small signal molecules
• Multiple active sites (multi-subunit)
• Binding at regulatory site induces
conformational change that affects active site
• Activity at one active site affects other active
sites, known as co-operativity

35
Q

Allosteric Regulation: T vs R & Co-operativity

A

Tense & Relaxed:
• T state – low affinity
• R state – high affinity

Co-operativity:
• Substrate binding to one subunit favours others becoming relaxed

36
Q

Allosteric Activators

A

Increase the proportion of enzyme in the R state

Shift curve to the left

37
Q

Allosteric Inhibitors

A

Increase the proportion of enzyme in the T state

Shift curve to the right

38
Q

Allosteric regulation of phosphofructokinase

A

Phosphofructokinase is allosterically regulated and sets the pace of glycolysis

It is the key regulator of glycolysis

Allosteric activators: AMP, fructose-2,6-bisphosphate

Allosteric inhibitors: ATP, citrate, H+

39
Q

Covalent Modification - Phosphorylation

A

Protein kinases transfer the terminal phosphate from ATP to the –OH hydroxyl group of Serine, Threonine, Tyrosine

40
Q

Covalent Modification - Dephosphorylation

A

Protein phosphatases reverse the effects of kinases

They do this by catalysing the hydrolytic removal of phosphoryl groups from proteins

41
Q

Clinical Significance of Enzymes (2)

A

Drug Targets
Biomarkers

42
Q

Clinical Significance of Enzymes: Drug Targets

A

Angiotensin converting enzyme inhibitors (e.g. Enalapril) – mainstay of the treatment of hypertension

Inhibitors of dihydrofolate reductase (e.g. methotrexate) causes cells to arrest in S phase of cell cycle and die – some cancers and rheumatoid arthritis

43
Q

Clinical Significance of Enzymes: Biomarkers

A

Liver function tests measure a range of hepatic enzymes along with plasma
levels of other substances

Creatine kinase is a marker of muscle damage

Molecules, Genes and Diseases (15 decks)

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