enzymes

Question 1

what are enzymes

Answer 1

• enzymes are proteins that catalyse biological reactions

- speed up reactions without being permanently altered

Question 2

how do enzymes work

Answer 2

• enzymes bind substrates in their active sites and convert them into products
• the substrates are bound to specific regions in the active site

Question 3

what is energy called needed to form the product

Answer 3

• activation energy

Question 4

how do enzymes lower the activation energy

Answer 4

• by stabilising the complex which then increases the rate of reaction

Question 5

what are covalent inhibitors

Answer 5

• form covalent bonds with functional groups in active site and selectively inhibit enzymes

Question 6

what is the binding of a substrate determined by

Answer 6

• electrostatic interactions

Question 7

what factors can alter enzyme activity

Answer 7

• ph
• temperature
• substrate concentration

Question 8

what does a change in ph do to enzyme activity

Answer 8

• alters the properties of functional groups within the active site and therefore change interactions
• different enzymes have different optimum ph values according to their function

Question 9

how does a change in temp affect enzyme activity

Answer 9

• as temp increases the speed of reaction increases, increasing no of collisions and therefore the number of enzyme substrate complexes being formed
• but at too high of a temp change the bonds break within the enzyme changing shape of active site

Question 10

how does a biological catalyst differ from chemical catalyst

Answer 10

• high reaction rates
• greater specificity
• can be regulated
• milder reaction conditions

Question 11

substrate specificity

Answer 11

• the specificity of a reaction is a result of 3d arrangement of amino acids in the active site
• even if the shape is the same but the charge is different there will be no binding

Question 12

what are co factors

Answer 12

• help enzyme substrate complexes form

- co factors are preserved

Question 13

what are the two main types of co factors

Answer 13

• co enzymes

- metal ions

Question 14

how are coenzymes synthesised and purpose

Answer 14

• usually synthesised from vitamins
• symptoms of vitamin deficiency due to loss of enzyme activity
• transfer of chemical groups
• can aid oxidation - reduction reactions

Question 15

what do metal ions do

Answer 15

• helps bind substrate by coordinating negatively charged groups
• can accept and donate electrons in oxidation and reduction reactions

Question 16

substrate conc

Answer 16

• rate of reaction increases with substrate concentration until saturation when maximum velocity is reached

Question 17

how is the relationship between substrate concentration and reaction velocity described by

Answer 17

• Michaelis - menton equation
  v = Vmax (s) / Km + S
• km is a measure of the affinity an enzyme has for its substrate - low km = high affinity
• together with Vmax it can be used to determine the nature of a particular inhibitor

Question 18

why is it important to know the affinity of an enzyme

Answer 18

• helps identify its physiological role
• helps design and study effect of a drug
  eg. statins - which is used to reduce high cholesterol levels in the blood
• competitively inhibit HMG co - reductase, enzyme required for cholesterol synthesis

Question 19

4 regulations of enzyme activity

Answer 19

• allosteric interaction
• covalent modification
• protein - protein interaction
• proteolytic cleavage

Question 20

allosteric interaction

Answer 20

• enzymes are allosteric - that they are inhibited or activated by molecules binding to them at a site other than the active site
• this binding alters the shape of the active site by changing the overall shape of the enzyme

Question 21

what are the two types of allosteric inhibitors

Answer 21

• homotrophic

- heterotrophic

Question 22

what is homotrophic

Answer 22

• the substrate itself binds to the enzyme somewhere other than its active site
• generally positive effectors

Question 23

what is heterotrophic

Answer 23

• a molecule other than the substrate binds to the enzyme away from the active site
• can be positive or negative
• often occurs as feedback inhibition

Question 24

why is allosteric important

Answer 24

• important in regulation of metabolic pathways which are often regulated by the rate of one key enzyme

Question 25

what does protein kinase a and how is regulated

Answer 25

• activates a range of enzymes in different pathways
• regulated by hormones via allosteric regulator, cAMP
• cAMP binds to regulatory subunits of PKA, releasing active enzyme

Question 26

what is covalent modification and why is it important

Answer 26

• involved addition and removal of phosphate group
• important for many cellular processes
• phosphorylation catalysed by another group of enzymes called kinases which use atp
• dephosphorylation carried out by phosphatases
• can positive or negatively influence enzyme activity

Question 27

protein - protein interaction

Answer 27

• changes shape of active site resulting from interaction w another protein
• contains a hinge region which allows it to fold over target enzyme
• calcium ions can also bind many amino acids to cause conformational changes
• ca2+ a binding protein, calmodulin

Question 28

regulation of expression

Answer 28

• level of enzyme present in a cell is tightly regulated
• can be controlled at level of synthesis or degradation
• transcription of rna encoding enzyme can be stimulated or repressed
• stability of transcript can be regulated
• rate of decay can be regulated

Question 29

proteolytic cleavage

Answer 29

• some enzymes have a portion of their structure must be split to become functional
• example proteases
• synthesised as inactive ‘zymogen’ to prevent damage to cell
• only come by active when cut by another enzyme

Question 30

enzymes in medicine

Answer 30

• enzymes target of many drugs eg aspirin
• most enzymes present in plasma
  ; changes in levels of activity of these enzymes are associated w various diseases
  ; plasma level of particular enzymes can be used as diagnostic tool

Question 31

enzymes in heart disease

Answer 31

• creatine kinase occur in three forms (isoenzyme)
  ; mm
  ; mb
  ; bb
• mb is exclusively expressed in heart muscle
• appearance of this isoenzyme in the blood is specific of myocardial infarction (heart attack)