Enzymes 1

Question 1

What are enzymes?

Answer 1

Are proteins that speed up (catalyse) specific chemical reactions

Question 2

What are some general functions of enzymes?

Answer 2

Digestion 
Blood clotting 
Defence-immune system 
Movement 
Nerve conduction

Question 3

What is function of nucleases?

Answer 3

Break down nucleic acid

Question 4

What is function of proteases?

Answer 4

Hydrolyse peptide bond of other proteins

Question 5

What is function of kinase?

Answer 5

Add phosphates to other substrates

Question 6

Enzyme defects can cause inherited disease

Give examples of these diseases

Answer 6

Tays-Sachs disease=>amino acid deficiency. Are unable to cerebioside
Glycogen storage disease=> mutation of enzyme that mobilises glucose into blood
Phenylketonuria=> deficiency in liver enzymes enzyme. Phe can’t be broken down /converted into toxin in brain

Question 7

Enzyme are drug targets

Give examples of such drugs

Answer 7

Antibiotics e.g. penicillin inhibits cell wall synthesis
Anti-inflammatory agents e.g. aspirin blocks enzyme that makes prostaglandin.
Anti cancer drugs e.g. methotrexate kills some types of cancer. Elle by shutting down dihydrofolate reductase

Question 8

What are the key enzyme properties?

Answer 8

Increase reaction rate 
Show specificity 
Unchanged at end of reaction
Don’t alter reaction at equilibrium 
Facilitate reaction by decreasing free energy of activation of reaction

Question 9

What is an active site?

Answer 9

3D cavity or cleft that binds to substrate using electrostatic, hydrophobic, hydrogen bonding + VDW interactions

Question 10

What is evidence that enzymes have active sites come from?

Answer 10

X-ray crystallography-> see where in enzyme substrate binds

Kinetics studies of enzyme activity

Question 11

In what cells are Ras protein mutated?

Answer 11

In tumour cells
Effect is that it stops GTPase from working + Ras protein to stay switched in due to lack of hydrolysis of GTP. This means that Ras can communicate to all other proteins in cell + tell the cell to grow

Question 12

How is RAS protein inactivated?

Answer 12

By hydrolysis of GTP

GTP-> GDP + Pi

Question 13

What are E-S binding energy used for?

Answer 13

To bring molecules together in active site
To constrain substrate movement
Stabilise +ve and -ve charges in transition state
To strain particular bonds in substrate=>making breakage easier
Use co factors=> bring new chemistry. React chemically with substrate + change pathway by which reaction goes

Question 14

What is lysozyme?

Answer 14

Enzyme that acts as a natural antibiotics egg white, saliva + tears

Question 15

What is function of lysozyme?

Answer 15

It severs polysaccharide chains that form cell walls of bacteria

Question 16

What is reaction catalysed by lysozyme?

Answer 16

Hydrolysis
Enzyme adds water molecule to single bond between 2 adjacent sugar groups in polysaccharide chain thereby causing bond to break
For colliding water molecule to break bond linking 2 sugars, polysaccharide molecule has to be distorted into a particular shape (transition state) in which atoms around bond have altered geometry + electron distribution

Question 17

Why is hydrolysis slow?

Answer 17

Because in aqueous solutions at room temp, energy of such collisions almost never exceeds activation energy

Question 18

What is Km?

Answer 18

Concentration of substrate when reaction reaches half of Vmax

Question 19

What is Vmax?

Answer 19

Maximum rate when enzyme is saturated with substrate

Question 20

Small Km means ……

Answer 20

Higher affinity as low concentration of substrate is required to reach half of Vmax

Question 21

What happens to Km and Vmax in competitive inhibition?

Answer 21

Vmax is unaltered

Km is increased

Question 22

What happens to Km and Vmax in non competitive inhibition?

Answer 22

Vmax is decreased

Km is unaltered

Question 23

What is feedback inhibition and what happens?

Answer 23

In feedback inhibition, an enzyme acting early in reaction pathway is inhibited by late product of that pathway
Wherever large quantities of final product begins to accumulate, product binds to an earlier enzyme + slows down its catalytic action, limiting further entry of substrates into that reaction pathway More products, the more it inhibits

Question 24

Feedback inhibition is ……… regulation.

Answer 24

Negative regulation

It prevents enzyme from acting

Question 25

Enzymes can also be subject to ….. regulation

Answer 25

Positive regulation
In which enzyme’s activity is stimulated by a regulatory molecule rather than being suppressed.
It occurs when product in one branch of metabolic maze stimulates activity in another pathway

Question 26

Describe the structure of allosteric enzymes?

Answer 26

Have 2 or more binding sites that influence each other
Multi subunit complexes
Regulatory sites + catalytic sites are on different subunit=> regulatory molecule often has a shape that is totally different from shape of enzyme’s preferred substrate
Regulation occurs via conformational changes
Exhibit non-Michaelis-menten kinetics
Involved in feedback inhibition of metabolic pathway