energetics and enzymes

Question 1

define enzyme

Answer 1

protein acting as catalyst to induce chemical changes in other substances, but remains unchanged by process; increases rate or reaction; high specificity; delta G remains same but lowers Ea

Question 2

hydrolase

Answer 2

catalyse hydrolytic cleavage

Question 3

dehydrogenase

Answer 3

oxidise substrate by reducing coenzyme

Question 4

protease

Answer 4

hydrolyse peptide bonds

Question 5

nuclease

Answer 5

hydrolyse phosphodiester bonds

Question 6

ligase

Answer 6

joins two molecules together

Question 7

transferase

Answer 7

transfer functional groups

Question 8

isomerase

Answer 8

rearrange bonds within molecule

Question 9

polymerase

Answer 9

catalyse polymerisation reactions

Question 10

kinase

Answer 10

catalyses phosphorylation and activation

Question 11

phosphatase

Answer 11

hydrolytic removal of phosphate

Question 12

oxido-reductase

Answer 12

one oxidised, one reduced (type of dehydrogenase)

Question 13

ATPase

Answer 13

hydrolyses ATP

Question 14

glucose-6-phosphatase

Answer 14

catalysed aq reaction of glucose-6-phosphate with water to form glucose and Pi

Question 15

lysozyme: function

Answer 15

hydrolyses B(1-4) bond in peptidoglycan (NAG and NAM) so bacteria lyse and die

Question 16

requirements of Glu-35 and Asp-52 to ensure maximum rate of lysozyme hydrolysis

Answer 16

Glu-35 is protonated and Asp-52 is ionised, so +ve transition can be stabilised

Question 17

mechanism of Glu-35 and Asp-52

Answer 17

Glu-35 protonates the oxygen in the glycosidic link between the two sugars, breaking the glycosidic bond; water molecule enters and is deprotonated by Glu-35; Asp-52 stabilises the positive charge in the transition state; OH- attacks the remaining sugar molecule, adding an OH group to it; proton is transferred to Glu-35 to return it to it’s original state; Glu-35 and Asp-52 are both in their original state to continue catalysis

Question 18

lock and key hypothesis

Answer 18

substrate shapes exactly complementary to active site

Question 19

induced fit hypothesis

Answer 19

substrate induces change in active site (proteins possess degree of flexibility)

Question 20

effect of pH on catalysed reactions

Answer 20

optimum pH, sharp decrease either side as enzyme denatures

Question 21

effect of T on catalysed reactions

Answer 21

slow increase in rate as gain kinetic energy, optimum T, rapid decline as enzyme active site denatures

Question 22

effect of [substrate] on catalysed reactions

Answer 22

increases until [enzyme] or other factors become limiting