Enzymes and coenzymes

Question 1

what is an enzyme?

Answer 1

biological catalysts which speed up rate of reaction - without altering the final eqm between reactants and products
they are not used up and are regenerated

Question 2

are enzymes efficient?

Answer 2

extremely - catalase catalyses break down of H2O2 to water 10^4 times faster than the uncatalyzed reaction at 30C

Question 3

how do enzymes catalyse reactions?

Answer 3

they provide an alternative pathway for the reaction with a lower activation energy

• binding energy decreases overall energy by stabilising the transition state, orienting the substrates correctly and distorting reactants to a reactive state
• it is reversible reaction

Question 4

what is an isoenzyme?

Answer 4

enzymes that catalyse the same reaction but are different gene products

Question 5

what does enzyme specificity mean

Answer 5

enzymes will only catalyse one reaction with specific substrate(s), including differences in stereoisomers

Question 6

what is specificity determined by?

Answer 6

the shape of the active site where only the correct shaped and charged substrate can fit

Question 7

what are the consequences of enzyme specificity?

Answer 7

group of enzymes present together in one compartment of a cell e.g. cytoplasm of muscle cells, can give rise to a complex and co-ordinated metabolic pathway

Question 8

what are the 6 main classes of enzyme?

Answer 8

oxidoreductase
transferase
lyase
hydrolase
isomerase
ligase

Question 9

what does oxidoreductase enzyme do?

Answer 9

catalyse transfer of H atoms and electrons (redox reactions)

Question 10

what does transferase enzyme do?

Answer 10

catalyse transfer of functional groups from donors to acceptors

Question 11

what does lyase enzyme do?

Answer 11

catalyse cleavage of C-C, C-O, C-N bonds (addition of groups to double bonds or formation of double bonds by removal of groups)

Question 12

what does hydrolase enzyme do?

Answer 12

catalyse cleavage of bonds by addition of water (hydrolysis)

Question 13

what does isomerase enzyme do?

Answer 13

catalyse transfer of functional group within the same molecule

Question 14

what does ligase enzyme do?

Answer 14

use ATP to catalyse formation of new covalent bonds

Question 15

what are the other three enzymes and what do they do?

Answer 15

phosphorylase - addition of inorganic P group
kinase - addition of P from ATP
phosphatase - removal of P group

Question 16

what is the structure of an enzyme?

Answer 16

tertiary proteins - folded into complex 3D structures

stabilised by many weak bonds

Question 17

what bonds stabilise enzymes?

Answer 17

H bonds, ionic bonds, hydrophobic interactions

Question 18

what are the weak bonds in enzymes affected by?

Answer 18

easily broken
affected by temp and pH
generally sensitive to their environment

Question 19

what determines the shape of the active site?

Answer 19

amino acid side chains
- they are involved in the formation of ESCs
other parts if aa are used to channel the enzyme to the active site as part of the catalysis process

Question 20

what are the two models that allow binding of substrate to AS?

Answer 20

lock and key

induced fit

Question 21

how does lock and key work?

Answer 21

substrate fits directly into active site

Question 22

how does induced fit work?

Answer 22

conformation of the enzyme

• substrate binds in closed configuration
• active site forms around the substrate

Question 23

how does temp affect enzymes?

Answer 23

• ROR inc up until the optimum temperature

- rate then dec as weak bonds in tertiary structure are broken so enzyme denatures and loses active site

Question 24

hoe does pH affect enzymes?

Answer 24

pH affects the weak bonds and so ROR will be fastest at optimum pH
-pH changes cause reversible changes to the enzyme as they will accept/donate a proton depending on the environment

Question 25

what is a co factor?

Answer 25

any substance that is required for an enzyme to be catalytically active

Question 26

what are coenzymes?

Answer 26

organic cofactors e.g. NAD

Question 27

what do co substrates do?

Answer 27

transfer groups from one enzyme to another

Question 28

what are prosthetic groups and their function?

Answer 28

co factors that are tightly bound to the enzyme and remain attached to it when catalysing the reaction; remain unchanged at the end of the reaction cycle