Enzymes in Physiology

Question 1

Define Enzyme

Answer 1

Enzymes are protein catalysts that speed up the rate of biochemical reactions without being changed or used up.

Question 2

Enzymes provide..

Answer 2

A reaction surface (active site)

A suitable environment.

Question 3

What do enzymes actually do?

Answer 3

They decrease the activation energy. More molecules meet this energy leading to an increased rate of reaction.

Question 4

Every chemical energy is accompanied by…

Answer 4

a change in free energy, (Gibbs free energy)

Question 5

Gibbs free energy equation

Answer 5

(free energy of initial state) - (free energy of final state)

Question 6

What is active site?

Answer 6

A region within an enzyme that fits the shape of substrate molecules.

Question 7

How do substrates bind?

Answer 7

Amino acid side-chains align to bind the substrate through H-bonding and hydrophobic interactions.

Question 8

When are products released?

Answer 8

When the reaction is complete as they no longer fit well in the active site.

Question 9

2 Binding Hypothesises:

Answer 9

Lock and key (rigid structure)

Induced Fit (more flexible and changes shape upon a drug.)

Question 10

Enzymes optimum pH

Answer 10

7.4

Question 11

What happens at low or high pH?

Answer 11

Activity as lost as tertiary structure is disrupted.

Question 12

Changing the pH alters.. (3)

Answer 12

the ionization state of amino acid side chains

ionic bonding, structural stability, shape and functionality of enzyme

overall 3D structure of all enzymes

Question 13

Enzymes optimum temperature

Answer 13

37 degrees

Question 14

What are cofactors?

Answer 14

Non-organic molecules that bind to the active site and facilitate the reaction by maintaining correct configuration of active site.

Question 15

Polypeptide proportion of the enzyme is called..

Answer 15

Apoenzyme

Question 16

What are coenzymes?

Answer 16

Organic molecules bound to the enzyme by weak interactions or H bonds - many have modified vitamins in their structure and carry electrons.

Question 17

All enzymes end in …

Answer 17

-ase

sucrase
catalyses the hydrolysis of sucrose

Question 18

Describe Oxido-reductases

Answer 18

Catalyse transfer of electrons from donors to acceptors (oxidation and reduction reactions)

Question 19

Oxido-reductases

Dehydrogenases

Answer 19

Accept and donate electrons as hydride ions or hydrogen atoms often using cofactors such as NAD+/NADH as an electron donor to acceptor.

Question 20

Describe Transferases

Answer 20

Catalyse transfer of a specific functional group between molecules.

Question 21

Transferases

1- What do Kinases do?
2 - What do Aminotransferases do?
3 - Glycosyltransferases?
4 -Acyltransferases?

Answer 21

1- kinases - transfer phosphate groups

2 - transfer amino groups

3 - transfer carbohydrate residues

4 - transfer fatty acyl groups

Question 22

Describe Hydrolases

Answer 22

Catalyse cleavage of bonds by the addition of a water molecule

Question 23

Hydrolases

1- What do phosphates do?
2 - Lipases?
3 - Peptidases?

Answer 23

1 - hydrolyse phosphoric ester bonds

2- hydrolyse ester bonds in lipids

3 - hydrolyse peptide bonds to form 2 products.

Question 24

Describe Lysases

Answer 24

Catalyse the addition of water, ammonia or CO2 to double bonds or remove them to create double bonds

Question 25

Lysases 1- Decarboxylases? 2 - Dehydrases? 3- Deaminases?

Answer 25

1- remove CO2 2- remove H2O 3 - remove NH3

Question 26

Describe Isomerases

Answer 26

Catalyse the interconversion of isomeric forms of a molecule by transferring groups within the same molecule e. g. Cis and Trans molecules e. g. D and L isomers

Question 27

Describe Ligases

Answer 27

Catalyse the synthesis of new covalent bonds using ATP energy

Question 28

Enzymes may recognise and catalyse.... (3)

Answer 28

Absolute - one type of reaction for a single substrate Group - one type of reaction for similar substrates Linkage - one of type of reaction for a specific type of bond

Question 29

Example of Absolute catalysis

Answer 29

Urease catalyses only hydrolysis of urea

Question 30

Example of Group catalysis

Answer 30

Hexokinase adds phosphate groups to hexoses

Question 31

Example of Linkage

Answer 31

Trypsin catalyses hydrolysis of peptide bonds

Question 32

Active site conformation drives selectivity Chymotrypsin prefers...

Answer 32

aromatic side chains adjacent to scissile bond

Question 33

Active site conformation drives selectivity Trypsin prefers...

Answer 33

positively charged side chains that can interact with Asp189

Question 34

Active site conformation drives selectivity Elastase prefers...

Answer 34

small uncharged side chains, as pocket is blocked

Question 35

What are isoenzymes?

Answer 35

Different forms of an enzyme catalysing same reaction in different tissues.

Question 36

Are there any differences between isoenzymes?

Answer 36

Slight variations in quaternary structure - different physical attributes and optimal conditions.

Question 37

Give an example of isoenzymes

Answer 37

LDH1 - in heart muscle converts lactate to pyruvate, and then to Acetyl coA LDH5 - in skeletal muscle converts lactate to pyruvate.

Question 38

Positive allosterism is when...

Answer 38

Some effectors speed up enzyme action

Question 39

Negative allosterism is when...

Answer 39

Some effectors slow enzyme action.

Question 40

Structure of allosteric enzyme

Answer 40

Quaternary structure with two different sites of attachment - the active site and the effector binding sit

Question 41

How does Allosteric regulation of enzyme action work (3)

Answer 41

Enzyme complex attaches to the substrate at the active site - releases product. One product functions as a negative feedback effector by fitting into the effector binding site. Binding of the effector in the effector binding site causes a conformational shift of the enzyme that closes the active site and inactivates the enzyme.

Question 42

Allosteric enzymes are basis for...

Answer 42

feedback inhibition.

Question 43

What happens in feedback inhibition?

Answer 43

A product serves as an inhibitor for a previous allosteric enzyme earlier in the series.