Enzymes Flashcards

1
Q

What are globular proteins?

A

Polypeptide chains folded into a compact shape like a ball with an irregular surface
Complex tertiary and quaternary structure

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2
Q

What are fibrous proteins?

A

Individual molecules that span a large distance
Simple 3D structure

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3
Q

What is an enzyme?

A

A globular biological catalyst that speeds up metabolic reactions without being changed in the process

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4
Q

What are enzymes needed for?

A

Metabolism, movement, digestion, cell signalling and gene expression

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5
Q

What is a kinase enzyme?

A

These add phosphate ions to molecules

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6
Q

How are enzymes involved in disease?

A

May disrupt homeostasis e.g. PKU - rare genetic disorder caused by mutation leading to seizures and behavioural problems

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7
Q

What is the active site?

A

It is a cleft on the protein
It is non polar
Has specific amino acids that allow substrate to bind and others for catalysis

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8
Q

What is the induced fit model?

A

when substrates bind to the enzyme active site it will change its shape slightly so the chemical reaction can occur with the lowest energy possible

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9
Q

What is the allosteric site?

A

Away from the active site and is where regulatory molecules bind which can activate or inhibit a molecule

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10
Q

What is a co-factor?

A

Any inorganic factor required for enzyme activity e.g. metal ions for metalloenzymes

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11
Q

What is a coenzyme?

A

An organic molecule that is directly involved in enzyme catalysis e.g. lactate dehydrogenase

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12
Q

What is an apoenzyme?

A

Inactive - no coenzyme added

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13
Q

What is a holoenzyme?

A

Active - coenzyme added

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14
Q

What is a prosthetic group?

A

Non protein molecules that are associated with the enzyme via covalent bonds

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15
Q

What do oxidoreductases do?

A

Transfer oxygen or hydrogen atoms or electrons from one substrate to another

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16
Q

What do transferases do?

A

Transfer a functional group form one substrate to another

17
Q

What do hydrolases do?

A

Hydrolysis of substrate

18
Q

What do lyases do?

A

Addition or removal of a group to form a double bond

19
Q

What do isomerases do ?

A

Transfer of groups within a molecule

20
Q

What do ligases do?

A

Bond formation coupled with ATP hydrolysis

21
Q

What is activation energy?

A

Amount of energy needed to start a reaction

22
Q

What is the transition state?

A

Highest energy level as the substrate is in the process of being converted to products (most unstable)

23
Q

What are 7 ways enzymes reduce activation energy?

A

Binding(collision theory) - substrates need to collide with each other with enough energy
Spatial complementarity- reactants in the right orientation
Induced fit- a.s. adjusts shape so substrate bound in best way
Chemical complementarity- specific a/a allow catalysis
Specific r groups - define shape of a.s
Exclude water
Weak forces- release enery

24
Q

What are the catalytic mechanisms?

A

Metal ion catalysis - metal ion aids catalysis
Catalysis by approximation- brings reactants closer together
Covalent catalysis- enzyme uses a transient bond to bind the substrate
Acid base catalysis- Hydrogen added or taken away for reaction to occur

25
What is the RoR / velocity ?
Amount of substrate converted to products per unit time
26
Outline the initial velocity
Units are µmol/min Fastest rate, high concn of substrate, low products, low feedback inhibition
27
What is the Michaelis constant?
Measure of affinity of the substrate to the enzyme- how readily the substrate binds to enzyme
28
How to calculate Km
1. Vmax line to Y axis 2. Half of Vmax line - line down to the x axis 3. Km- concn of substrate when Vmax is at its half point
29
What does a high Km mean?
Weak binding Low affinity High concn of substrate to reach Vmax
30
What is the effect of temperature on RoR?
Increase in thermal energy so overcomes the Ae which increases rate BUT beyond optimal Rapid decrease in RoR as weak bonds broken altering active site enzyme denatured
31
How does pH impact enzyme activity?
Ionisation of groups in the active site
32
How are enzymes regulated?
- Controls how molecules of each enzyme it makes by regulating the expression of the gene that encodes that enzyme - Confining sets of enzymes to particular subcellular compartments - Covalently modified to control activity - Rate of protein destruction - Binding of small molecules
33
What is feedback regulation?
End products inhibit earlier pathway steps to prevent the build up of unnecessary metabolites
34
What is competitive inhibition?
Inhibitor is a similar shape to the substrate so it binds to the active site of the, blocking the binding of substrates. Can be overcome by increasing substrate concn Km increases Affinity decreases Vmax same
35
What is non competitive inhibitors?
Inhibitor binds to the allosteric site causing conformational changes to the active site the binding of the substrate is the same BUT catalytic activity is decreased Km is the same Vmax is reduced
36
What is an uncompetitive inhibitor?
An inhibitor binds to the e.s complex thus inhibiting catalysis Km is reduced Vmax is reduced