Enzymes

Question 1

What is an enzyme

Answer 1

Protien that catalyses chemical reactions without itself being destroyed/altered - seek to lower the Ea

Question 2

What is different with enzyme catalysed reactions compared to chemical catlysts

Answer 2

Can be regulated

Question 3

Subvstrate

Answer 3

Reactant in catalysed reaction

Question 4

Active site

Answer 4

Part of enxyme that binds to substrate to form E-S complex

Question 5

product

Answer 5

Substance produced by enzyme-catalysed conversion of substrate

Question 6

Cofactor

Answer 6

non-protien component needed for the reaction (e.g. magnesium)

Question 7

Coenzyme

Answer 7

Heat-stable substance which can aid enzyme reactions

Question 8

Isoenzyme

Answer 8

enzymes that catalyse the same reaction but vary in structure and other biochemical properties

Question 9

Activation energy

Answer 9

Energy needed for the reaction to proceed

Question 10

How do enzymes inc the rate of reaction

Answer 10

by lowering the Ea

Question 11

How do enxymes lower the Ea (3)

Answer 11

• Entropy reduction - Enzymes force the substate to be correctly orientated by binding them in the formation they need to be in for the reaction to proceed
• Desolvation - weak bonds between S and E essentially replace most or all of the H-bonds between substrate and aqueous solution
• Induced fit - conformational changes occur in the protien structure where the substrate binds

Question 12

basic enzyme reaction

Answer 12

1. substrate enters active site of enzyme
2. forms an enzyme-substrate complex, enzyme changes shape slightly as substrate binds (induced fit)
3. forms an enzyme-product complex
4. products leave active site of enzyme

Question 13

Michaelis-Menton plot

Answer 13

V0= Vmax [S]/Km

V0= initial reaction velocity
Vmax= maximum reaction velocity
[S]= substrate concentration
Km= the substrate concentration when the reaction is at ½ the maximum velocity (Vmax)

Question 14

Michaelis-menton plot diagram

Answer 14

look one up

Question 15

What does Km measure

Answer 15

Specificity of enzyme for substrate

Question 16

What does a low/high Km value mean?

Answer 16

• Low = good fit
• High = poor fit (takes lots of substrate to get to 1/2Vmax)

Question 17

What does Vmax measure

Answer 17

how fast a reaction is proceeding when the enzyme is saturated with substrate

Question 18

What can affect enzyme reactions

Answer 18

• Enzyme concentration - inc, inc rate
• Substrate concentration
• Temp
• pH
• Inhibitors (competitive/non-competitive)

Question 19

What are competitive inhibitors

Answer 19

Inhibitor binds to AC of enzyme and prevents the substrate from binding

Question 20

What happens to Vmax and Km with competitive inhibition

Answer 20

• Vmax = unchanged
• Km = inc because it takes more substrate to overcome the inhibition

Question 21

What is non-competitive inhibiton

Answer 21

Inhibitor binds to a secondaty site on the enzyme which changes the shape of the AS and prevents the substrate from binding

Question 22

What happens to Vmax/Km during non-competitive inhibition

Answer 22

• Vmax = decreased
• Km = remains the same

Question 23

Why measure enzymes

Answer 23

• Detection of suspected disease at pre-clinical stage
• Confirmation of suspected disease and assessing severity
• Localisation of disease to organs
• Characterisation of organ pathology
• Assessing the response to therapy
• Organ function assessment
• Assessing genetic susceptibility to drug side effects
• Detection of inherited metabolic disease
• Detection of vitamin deficiencies**

Question 24

Factors to determine enzyme activity in serum/plasma

Answer 24

• age
• gender
• pregnancy
• race
• time of day
• genetics
• drugs
• disease process, progress and treatment e.g. surgery

Question 25

Serum enzyme concentrations

Answer 25

Although there are some enzymes secreted from cells, serum E conc generally **Low** and only rise when there is damahe to cells and release of contents

Question 26

what is the release of enzymes from cells triggered by - factors to determine E activity in serum/plasma

Answer 26

* hypoxia * cellular damage * physical damage * immune disorders * microbiological agents * genetic defects * nutritional disorders

Question 27

hypoxia

Answer 27

Loss of O2 supply due to occlusion, inadequate oxygenation, or O2 carrying capacity

Question 28

What could cause cellular damage

Answer 28

chemicals/drugs

Question 29

What could physical damage include

Answer 29

trauma, surgery, burns, radiation...

Question 30

Give some examples of immune disorders

Answer 30

anaphylaxis, automimmune diseases

Question 31

What could microbiological agents include

Answer 31

bacteria, viruses, fungi, protozoa, helminthhs

Question 32

WHat could nutritional disorders include

Answer 32

protien-calorie, vitiman, mineral deficiencies

Question 33

How do we analyse enzymes in the lab

Answer 33

* Rate of an enzyme-catalysed reaction is directly proportional to the amount of enzyme present * Progress of conversion of the substrate to product is monitored: Fixed-time - at an end-point Continuous - throughout * Often measurement of an end product using spectrophotometry - coloured end product * Electrophoresis - to determine type (origin)

Question 34

What are some problems with enzyme measurement

Answer 34

* Not specific i.e. can be found in more than one tissue in the body. * Particular requirements - temperature, pH etc. * Assays must be optimised to conditions E require

Question 35

In what clinical situations are enzymes used - clinical diagnosis

Answer 35

* tissue damage * Determine origin of affected tissue * Disease related to enzyme defects

Question 36

What are some facts/conditions of enzyme use clinically

Answer 36

* often not specific * need particular conditions for measurement

Question 37

Why is enzyme activity measured in a clinical setting

Answer 37

enzyme assays are valuable for diagnosis of several diseases in clinical settings due to their high sensitivity, specificity, and rapid response.

Question 38

what factors can influence enzyme activity in samples

Answer 38

temperature, pH, enzyme concentration, substrate concentration, and the presence

Question 39

Michaelis constant definition

Answer 39

**the concentration of substrate that is transported at half the maximal velocity (Vmax) of transport**; a measure of the affinity of the transporter for its substrate.

Question 40

WHat does knowledge of the michaelis constant allow to be deduced about the **nature of the catlysed reaction**

Answer 40

A measure of how well a substrate complexes with a given enzyme, otherwise known as its binding affinity.