Enzyme properties and enzyme regulation

Question 1

Describe what enzymes are?

Answer 1

Biological Catalysts- increase the rate of reaction whilst not altering the final equilibrium between products and reactants. The decrease the time for the transition state
They are ere extremely efficient- eg. catalase with hydrogen peroxide breakdown

Enzymes are proteins ( and share similar properties- stabilised by weak non covalent bonds)
They are sensitive to pH changes and temperature changes
The active site contains functional groups that stabalise the Transition state of the reaction

NB this is done by providing an alternative reaction pathway - makes the reaction more kinetically favourable

Question 2

Why is important the product has low affinity for active site

Answer 2

less time in the Enzyme-Product complex- greater turnover for enzyme-substrate complex

Question 3

What is an active site?

Answer 3

A cleft/groove with a defined shape only substrate can fit in
The active site contains functional groups that stabalise the Transition state of the reaction

Question 4

What does specificity spend on?

Answer 4

It depends on the shape of the active site where only the substrate of the correct shape and charge can fit

Question 5

Describe how specific enzymes can be

Answer 5

Enzymes will catalyse one type of reaction
e.g Alcohol dehydrogenase oxidising primary alcohol to aldehydes
Will act on a few related molecules
Will act only on one substrate - absolute specificity
When stereoisomers exists with a natural compound
e.g. D glucose and L-glucose only the enzyme concerned with metabolism in the cell will usually act on one isomer

Question 6

When can specificity be useful?

Answer 6

When a group of enzymes are together in one compartment-
eg. cytoplasm of a muscle cell
The initial substance D glucose converted through a sequence of enzyme catalysed reactions to produce lactic acid

Question 7

Name the types of classes enzymes can be organised in

Answer 7

Hydrolyses
Oxidoreductases 
Ligases
Transferases
Isomerases 
Lysases

Question 8

Hydrolyse

Answer 8

catalyse the cleavage of bonds by addition of water

Question 9

Oxidoreductases

Answer 9

catalyse the removal of Hydrogens and electrons

eg. lactate dehydrogenase

Question 10

Ligases

Answer 10

use ATP to catalyse the formation of new covalent bonds

Question 11

Transferases

Answer 11

catalyse the transfer of functional groups from donors to acceptors eg. Alanaine amino transferase

Question 12

Isomerases

Answer 12

catalyse the transfer of functional group within the same molecule eg. phosphoglucose isomerase

Question 13

Lyases

Answer 13

catalyse the cleavage of C - C , C - O , C -N

eg. ATP citrate lyase

Question 14

Explain what is meant by the Lock and Key model

Answer 14

Enzyme has a defined rigid active site- substrate with the right shape will be complementary and fit perfectly

Question 15

Explain what is meant by the Modified Lock and Key model

Answer 15

Similar to the original, the substrate changes shape ( conformational change) making the substrate more reactive BUT the active site still remains rigid

Question 16

Explain what is meant by the Induced fit model

Answer 16

The active site is flexible making the shape of substrate and active site more complementary

Question 17

What is a catalytic triad

Answer 17

A catalytic triad is a set of three coordinated amino acids that can be found in the active site of some enzymes. Catalytic triads are most commonly found in hydrolase and transferase enzymes.

eg. Chymotyrpsin - Ser, His, Asp all linked via hydrogen bonds

Question 18

Explain the catalysis of peptide bond hydrolysis by chymotrypsin

Answer 18

see notes

Question 19

How does temperature effect enzymes?

Answer 19

20-40 degrees celsius- Increases the rate of product formation- by increasing the kinetic energy and increases the rate of formation of E- S complex rate
more likely to meet the activation energy

40-50 degrees celsius- less product formed as increasing the KE increases the distance between Ser and His in catalytic triad which means that theres no formation of H bonds- NO TS formed

Question 20

Comment on pH in regards to enzymes

Answer 20

Different enzymes will have different optimum pH.

Question 21

What are co factors?

Answer 21

a substance whose presence is required for the activity of enzymes

Question 22

Give examples of co factors

Answer 22

Inorganic elements-
Cu2+ -cytochrome oxidase
Fe2+/3+ - cytochrome oxidase, catalase and peroxidase
K+ - pyruvate kinase
Mg2+ - hexokinase, G-6-phosphate, pyruvate kinase
Se - gluthione peroxidase
Zn 2+ - carbonic anhydrase, alcohol dehydrogenase
Ni 2+ - Kinase

Question 23

What are coenzymes?

Answer 23

They can help transfer compounds between enzymes.
Coenzymes also help attract the correct compounds and repel incorrect compounds to the active site of their enzyme.
Enzymes are a type of cofactor that can attach itself to the active site temporarily- this means that the enzyme is activated

Question 24

What are Isoenzymes?

Answer 24

Enzymes with different protein structures catalyse the same reaction-

these enzymes are coded by different genes
and are often found in different compartments in cells

eg. Lactate dehydrogenase- heart vs muscle- different functions