Enzymes 1

Question 1

What is the definition of an enzyme?

Answer 1

Proteins that catalyse specific reactions

Question 2

Give some functions of enzymes

Answer 2

Digestion
Blood clotting
Immune system
Movement
Nerve conduction

Question 3

How are enzymes categorised?

Answer 3

According to which reaction they promote

Question 4

Give examples of enzyme categories

Answer 4

Protease
Nuclease
Polymerase
Kinase

Question 5

Give some examples of enzyme disfunctions that cause disease

Answer 5

Phenylketonuria
Glycogen storage disease
Tay-Sachs disease
Glycosphingolipid

Question 6

What does phenylketonuria mean?

Answer 6

Cannot convert Phe into Tyr

Question 7

What does glycogen storage disease mean?

Answer 7

Cannot mobilise (breakdown) glucose

Question 8

What does Tay-Sachs disease mean?

Answer 8

Defect in processing a membrane ganglioside causing neuronal damage

Question 9

What is a ganglioside?

Answer 9

A molecule composed of a glycosphingolipid with one or more sialic acids linked on the sugar chain

Question 10

How does penicillin target enzymes?

Answer 10

Inhibit cell wall synthesis

Question 11

How does aspirin block enzymes?

Answer 11

Blocks prostaglandin

Question 12

How does methotrexate block enzymes?

Answer 12

Interferes with the synthesis of DNA precursors

Question 13

Give the key properties of an enzyme

Answer 13

Increase reaction rate
Shows specificity
Unchanged at the end of the reaction
Do not alter the reaction equilibrium 
Facilitate reaction by decreasing the free energy of activation of the reaction

Question 14

How much do enzymes increase the reaction rate by?

Answer 14

10 billion fold

Question 15

What is the transition state?

Answer 15

The place where if you fall backwards you would have the reactants and if you move forwards you will get the products of the reaction

Question 16

What is an active site?

Answer 16

It is a 3D cavity that binds substrates with specificity through electrostatic, hydrogen, van def waals and hydrophobic interactions forming an E-S complex

Question 17

Give evidence for active sites

Answer 17

X-ray crystallography

Kinetic studies of enzyme activity

Question 18

Give the steps in X-ray crystallography

Answer 18

• make lots of the protein using DNA recombination technology
• get it to crystallise
• put crystals in an intense X-ray beam at a single wavelength

Question 19

How do you get an image using X-ray crystallography

Answer 19

The X-rays defract into a detector with photographic film on the other side.
You get a diffraction pattern that can b spit through software to get a molecular shape

Question 20

Why do you need an E-S binding energy?

Answer 20

• to bring molecules together in the active site
• to constrain substrate movement
• to distort substrate so bonds are strained, making it easier to break
• To exclude water From the reaction site, making the reaction go faster
• to provide a reaction pathway of lower energy

Question 21

What happens when an enzyme is saturated?

Answer 21

The reaction velocity begins to plateau

Question 22

What does the Michaelis constant measure?

Answer 22

Substrate binding affinity ( how sticky the active site is to the substrate)

Question 23

How do you get Vmax and Km using a double reciprocal plot?

Answer 23

Measure v at various substrate concentrations

Plot 1/v versus 1/[s]

Intercept on the y axis = 1/vmax
Intercept on the x axis= km

Question 24

How do competitive inhibitors work?

Answer 24

Compete with the substrate for binding to the active site, forming an EI complex

Question 25

What is an EI complex?

Answer 25

Enzyme- inhibitor complex

Question 26

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

Answer 26

Takes more substrate to achieve Vmax/2 but Vmax is the same as the inhibitor can be outcompeted at high concentrations

Question 27

What is non- competitive inhibition?

Answer 27

Inhibitor binds at a different site so doesn’t compete for binding at the active site

Question 28

What happens to km and vmax in the presence of a non- competitive inhibitor?

Answer 28

Km is unaltered but vmax is reduced

Question 29

How does control of gene expression regulate enzymes?

Answer 29

Limits the amount of enzyme made

Question 30

How does compartmentation regulate enzymes?

Answer 30

Sequences in enzyme polypeptide chain target enzyme to different organelles

Question 31

How does allosteric regulation regulate enzymes?

Answer 31

Changes the active site to increase or decrease enzyme activity - controls the flux of material through metabolic pathways

Question 32

How does covalent modification of the enzyme regulate enzymes?

Answer 32

Change enzyme shape and activity by (for example) phosphorylation

Question 33

What are the properties of an allosteric enzyme?

Answer 33

Multisubunit complexes
Regulatory and catalytic sites on different subunits
Regulation occurs by conformational changes
Exhibits non- Michaelis-menten kinetics
Involved in feedback regulation of metabolic pathways

Question 34

What shaped curve does an allosteric enzyme give?

Answer 34

Sigmoid

Question 35

What does novobiocin do?

Answer 35

It’s a competitive inhibitor to ATP as its binding site overlaps the ATP binding site

Question 36

What do fluoroquinolones do?

Answer 36

Inhibit DNA resealing by gyrase/topo IV - breaks the double strand (reversibly)