Enzymes

Question 1

What are ribozymes?

Answer 1

Catalytic RNA molecules with no protein component

Question 2

What is a cofactor?

Answer 2

A non-protein component needed for activity, usually metal ions

Question 3

What is a co-enzyme?

Answer 3

A complex organic molecule, usually produced from a vitamin FAD NAD+

Question 4

What is a prosthetic group?

Answer 4

A non-protein group forming part of or combined with a protein.

i.e - A cofactor covalently bound to an enzyme or very tightly associated with an enzyme

Question 5

What is an apoenzyme?

Answer 5

An inactive enzyme, activation of the enzyme occurs upon binding of an organic or inorganic cofactor.

Question 6

What is a holoenzyme?

Answer 6

WHole enzyme, the apoenzyme plus the cofactor

Question 7

Why isn’t a spontaneous reaction instantaneous?

Answer 7

Because of the activation energy barrier

Question 8

What is the activation energy used for?

Answer 8

Positioning chemical groups correctly

Question 9

What is the transition state?

Answer 9

The moment that chemical bonds are formed and broken The reaction from this point could then go to products or reactants

Question 10

What type of bonds occur between substrate and enzyme?

Answer 10

Non-covalent

Question 11

What is the active site complementary to?

Answer 11

The transition state

Question 12

How do enzymes reduce activation energy?

Answer 12

Entropy reduction
Desolvation
Induced fit

Question 13

How does entropy reduction reduce activation energy?

Answer 13

Molecules react by bumping into each other, enzymes orientate the substrates improving the chance of a successful collision and a resulting reaction

Question 14

How does desolvation decrease the activation energy?

Answer 14

H bonds with the substrate and the solution are replaced by the weak bonds between the substrate and the enzyme.

Question 15

How does induced fit decrease activation energy?

Answer 15

Conformational changes occur in the protein structure when the substrate binds

Question 16

Which part of an enzyme reaction occurs more slowly?

Answer 16

The second part of the equation, producing E and P from the enzyme substrate complex

Question 17

Which stage of an enzyme reaction is reversible?

Answer 17

The formation of ES from E and S K1 denotes the forward reaction K-1 denotes the reverse reaction

Question 18

What is Km?

Answer 18

It is the substrate concentration when the reaction velocity is exactly half of the max velocity

Question 19

On a lineweaver burke plot what does the y intercept represent?

Answer 19

1/VMax

Question 20

On a lineweaver burke plot what does the X intercept represent?

Answer 20

1/Km

Question 21

What does Km measure?

Answer 21

The ration of rate constant for breakdown of ES to E+S compared to the rate constant for formation of ES from E+S It gives you a clue to the affinity of the enzyme with it’s substrate

Question 22

What does a large Km value indicate?

Answer 22

Less stable ES complex

Question 23

Which enzyme activity fluctuates directly with blood glucose intake?

Answer 23

Glucokinase Catalyses Glucose + ATP to glucose - 6 - phosphate

Question 24

What is used to determine normal enzyme activity?

Answer 24

Arbitrary values such as 1U/ml or 100%

Question 25

How are enzymes separated?

Answer 25

Gel electrophoresis

Question 26

Where can you find creatine kinase?

Answer 26

In the heart Elevation of plasma CK2 is diagnostic for myocardial infarction

Question 27

What are the possible reaction mechanisms for enzymes with two or more substrates

Answer 27

Random or ordered with a ternary complex No ternary complex formation

Question 28

Describe the reaction involving a ternary complex Random order

Answer 28

Can bind to either substrate first Eventually complexes with both substrates Forms two products

Question 29

Describe the reaction involving a ternary complex Ordered

Answer 29

Attaches to one substrate first, it is the fed the other substrate

Question 30

Describe the reaction with no ternary complex formed

Answer 30

Reaction occurs with enzyme and substrate producing altered enzyme and a product Second reaction occurs with the altered enzyme and the second substrate, producing a second product

Question 31

What type of reactions have no ternary complex formation?

Answer 31

Transamination reactions

Question 32

How does temperature affect the function of an enzyme?

Answer 32

Increase temperature will increase molecule collisions and it will increases the internal energy of molecules Eventually denautres the enzyme

Question 33

How does pH alter the function of an enzyme?

Answer 33

pH changes the charge of an amino acid, can stop the active site functioning if the amino acids in the active sites change charge. Extreme pH will denature the enzyme pH will affect the substrates

Question 34

What effect does a competetive inhibitor have on the Vmax and Km?

Answer 34

Same Vmax Km increases (since affinity active site has for the enzyme substrate complex decreases)

Question 35

What is an example of a transition state anologue?

Answer 35

Oseltamavir

Question 36

What does a catalytic antibody resemble?

Answer 36

It resembles the active site of the original enzyme, since it is specific to a transition state molecule

Question 37

What effect do non-competitive inhibitors have on the Vmax and the Km values?

Answer 37

V max will decrease - inhibition remains the same regrdless of the change in substrate concentration Km remains the same as the substrate is still able to bind to the active site

Question 38

Which type of inhibitors bind in an rreversible manner?

Answer 38

Those that bind in a covalent manner

Question 39

Which enzyme in a pathway holds the regulatory step for that pathway?

Answer 39

Often the first one in the pathway

Question 40

What are the regulatory types of enzymes called?

Answer 40

Allosteric enzymes and covalently modified enzymes

Question 41

What is feedback inhibition?

Answer 41

When there is a build up of an end product in a pathway or a key junction in a pathway that ultimately slows down the entire pathway

Question 42

How is the change in the structure of an enzyme brought about in allosteric control?

Answer 42

An allosteric effector (usually a metabolite) binds non-covalently to a site on the enzyme that is not the active site, changing the enzymes structure

Question 43

What are the two different types of allosteric effectors?

Answer 43

Activators and inhibitors

Question 44

How does the concerted model show how a small amount of substrate increases an enzymes sensitivity to a substrate?

Answer 44

Concerted model suggests that enzyme sub-units are always flipping between two conformational formations Binding of S to one substrate locks the other subunits in the same conformation

Question 45

How do allosteric inhibitors and activators function in the concerted model?

Answer 45

Activators - stabilise the the open conformation, allowing S to bind more effectively Inhibitors - stabilise the ‘closed’ conformation and make it difficult for S to bind effectively

Question 46

How does the sequential model show how a small amount of substrate increases an enzymes sensitivity to a substrate?

Answer 46

Substrate binding causes a change in **_ONE_** sub unit, this causes a change in another sub-unit allowing it to bind to S more readily

Question 47

What enzymes are responsible for covalent modification?

Answer 47

Protein kinases (add phosphoryl groups to proteins) Protein phosphatases (remove phosphoryl groups)

Question 48

What do multiple phosphorylation sites allow?

Answer 48

Very fine control of enzyme funciton

Question 49

What is an inactive precursor of an enzyme called?

Answer 49

A proprotein or a proenzyme

Question 50

What can be produced when a proprotein is cleaved?

Answer 50

Proteases

Question 51

Give an example of a an enzyme that is regulated by proteolytic cleavage

Answer 51

Trypsin - activated in the small intestine Its precursor trypsinogen is formed in the pancreas

Question 52

Describe the bonding between a protein and : * A prosthetic group * A coenzyme

Answer 52

Prosthetic group - Tight bonding (sometimes even covalent bonds) Coenzyme - Loose bonding