Enzymes

Question 1

What are globular proteins?

Answer 1

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

Question 2

What are fibrous proteins?

Answer 2

Individual molecules that span a large distance
Simple 3D structure

Question 3

What is an enzyme?

Answer 3

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

Question 4

What are enzymes needed for?

Answer 4

Metabolism, movement, digestion, cell signalling and gene expression

Question 5

What is a kinase enzyme?

Answer 5

These add phosphate ions to molecules

Question 6

How are enzymes involved in disease?

Answer 6

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

Question 7

What is the active site?

Answer 7

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

Question 8

What is the induced fit model?

Answer 8

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

Question 9

What is the allosteric site?

Answer 9

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

Question 10

What is a co-factor?

Answer 10

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

Question 11

What is a coenzyme?

Answer 11

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

Question 12

What is an apoenzyme?

Answer 12

Inactive - no coenzyme added

Question 13

What is a holoenzyme?

Answer 13

Active - coenzyme added

Question 14

What is a prosthetic group?

Answer 14

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

Question 15

What do oxidoreductases do?

Answer 15

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

Question 16

What do transferases do?

Answer 16

Transfer a functional group form one substrate to another

Question 17

What do hydrolases do?

Answer 17

Hydrolysis of substrate

Question 18

What do lyases do?

Answer 18

Addition or removal of a group to form a double bond

Question 19

What do isomerases do ?

Answer 19

Transfer of groups within a molecule

Question 20

What do ligases do?

Answer 20

Bond formation coupled with ATP hydrolysis

Question 21

What is activation energy?

Answer 21

Amount of energy needed to start a reaction

Question 22

What is the transition state?

Answer 22

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

Question 23

What are 7 ways enzymes reduce activation energy?

Answer 23

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

Question 24

What are the catalytic mechanisms?

Answer 24

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

Question 25

What is the RoR / velocity ?

Answer 25

Amount of substrate converted to products per unit time

Question 26

Outline the initial velocity

Answer 26

Units are µmol/min
Fastest rate, high concn of substrate, low products, low feedback inhibition

Question 27

What is the Michaelis constant?

Answer 27

Measure of affinity of the substrate to the enzyme- how readily the substrate binds to enzyme

Question 28

How to calculate Km

Answer 28

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

Question 29

What does a high Km mean?

Answer 29

Weak binding
Low affinity
High concn of substrate to reach Vmax

Question 30

What is the effect of temperature on RoR?

Answer 30

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

Question 31

How does pH impact enzyme activity?

Answer 31

Ionisation of groups in the active site

Question 32

How are enzymes regulated?

Answer 32

• 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

Question 33

What is feedback regulation?

Answer 33

End products inhibit earlier pathway steps to prevent the build up of unnecessary metabolites

Question 34

What is competitive inhibition?

Answer 34

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

Question 35

What is non competitive inhibitors?

Answer 35

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

Question 36

What is an uncompetitive inhibitor?

Answer 36

An inhibitor binds to the e.s complex thus inhibiting catalysis
Km is reduced
Vmax is reduced