F cell Enzymes

Question 1

What are enzymes?

Answer 1

Proteins that speed up (catalyse) specific chemical
reactions

Question 2

What are some examples of enzyme functions?

Answer 2

• Digestion: carbohydrates, fats, proteins
• Blood clotting: fibrin clot catalysed by thrombin
• Defence-immune system-activation of complement
• Movement: muscle actomyosin is an ATPase
• Nerve conduction: membrane pumps for Na+, K+, Ca++

Question 3

What is phenylketonuria?

Answer 3

Inherited enzyme disorder where you cannot convert Phe to Tyr.

Question 4

What is glycogen storage disease?

Answer 4

cannot mobilise glucose

Question 5

What is tay-sachs disease?

Answer 5

defect in processing a membrane

Question 6

What the enzymes not alter?

Answer 6

Do not alter reaction equilibrium

Question 7

What do enzymes facilitate?

Answer 7

Facilitate reaction by decreasing the free energy
of activation of the reaction

Question 8

What do enzymes facilitate?

Answer 8

Facilitate reaction by decreasing the free energy
of activation of the reaction

Question 9

What is an enzyme active site and how does it bind with specific substrates?

Answer 9

The active site is a 3-D cavity or cleft that binds substrate(s) with specificity through electrostatic, hydrophobic, hydrogen bonding and van der Waals interactions.

Question 10

What are the evidence for active sites?

Answer 10

-X-ray crystallography
-Kinetic studies of enzyme activity

Question 11

Lock and Key mechanism?

Answer 11

The active site was thought to have a fixed structure (the lock), which exactly matched the structure of a specific substrate (the key).

Question 12

Induced fit mechanism?

Answer 12

This model suggests that an enzyme, when binding with its substrate, optimizes the interface through physical interactions to form the final complex structure.

Question 13

What does lysozyme use to cleave its bacterial substrate?

Answer 13

Lysozyme uses strain to cleave its bacterial substrate

Question 14

What does polysaccharide cleavage cause?

Answer 14

Polysaccharide cleavage causes bacterial rupture
and death

Question 15

How do we obtain Vmax and Km values?

Answer 15

We use a double recipricol plot
-Measure V (rate of product formation) at various substrate
concentrations. Plot 1/V versus 1/[S]. Intercepts on the axes
provide values for Vmax and Km.
-X intercept=-1/km
-y intercept=1/vmax

Question 16

What is a turnover number>

Answer 16

max no of substrate molecules handled per active
site per second. Carbonic anhydrase is a very efficient enzyme.

Question 17

What happens to the Km and Vmax values in the presence of a competitive inhibitor?

Answer 17

In the presence of a competitive inhibitor: Km is increased (it takes more substrate
to achieve Vmax/2). However, Vmax is unaltered as the effects of the inhibitor can
be competed out at high substrate concentrations.

Question 18

What is Km value?

Answer 18

Km value is that concentration of the substrate at which half of the active sites of the enzyme are occupied by the substrate

Question 19

What is the Vmax value?

Answer 19

Vmax is the rate attained when the enzyme sites are saturated with substrate, i.e. when the substrate concentration is much higher than the KM

Question 20

What happens to Km and Vmax value in the presence of a non-competitive inhibitor?

Answer 20

in the presence of a non-competitive
inhibitor, the substrate Km is unaltered; but the Vmax is reduced.

Question 21

How is enzyme activity regulated in cells?

Answer 21

1.Control of gene expression
2.Compartmentation
3.Allosteric regulation
4.Covalent modification of enzyme

Question 22

What does control of gene expresssion control in enzyme activity?

Answer 22

Control enzyme amount

Question 23

What does compartmentation in enzyme activity regulation do?

Answer 23

Sequences in enzyme polypeptide chain target enzyme to ER, mitochondrion, nucleus etc

Question 24

What happens in allosteric regulation for enzyme activity regulation?

Answer 24

a regulatory molecule (acting at a
pocket distinct from the active site) changes the enzyme
conformation to influence the active site and decrease (or in
some cases, increase) enzyme activity. Controls the flux
of material through a metabolic pathway.

Question 25

What happens in covalent modification of enzyme in enzyme activity regulation?

Answer 25

Change enzyme shape and activity-e.g. phosphorylation

Question 26

What regulates metabolic pathways?

Answer 26

Feedback inhibition regulates metabolic pathways

Question 27

What are allosteric enzymes?

Answer 27

Multisibunit complexes

Question 28

Where are the regulatory sites and catalytic sites located in allosteric enzymes?

Answer 28

Regulatory sites and catalytic sites on
different subunits

Question 29

What does regulation of allosteric enzymes occur via?

Answer 29

Regulation occurs via conformational changes

Question 30

What kinetics do allosteric enzymes exhibit and what graph does this give us in a V vs S plot?

Answer 30

Exhibit non-Michaelis-Menten kinetics:
V vs S plots are sigmoidal

Question 31

What are allosteric enzymes involved in ?

Answer 31

Involved in feedback inhibition of metabolic pathways

Question 32

What does bacterial DNA gyrase catalyse?

Answer 32

Gyrase catalyses ATP-dependent DNA supercoiling by a double- strand
DNA break.

Question 33

What is novobiocin and what does it do and how?

Answer 33

-Antibiotic
-Inhibits gyrase
-Novobiocin (green) competitively
inhibits the binding of ATP (pink)
to gyrase

Question 34

What does fluoroquinolones do?

Answer 34

Fluoroquinolones inhibit DNA resealing by gyrase/topo IV