Biochemistry - Outcome 2

Question 1

what are simple enzymes?

Answer 1

enzymes that are composed only of protein and require no other groups other than the amino acids for activity

Question 2

what are complex enzymes?

Answer 2

enzymes composed of protein plus a relatively small group which is required for activity

Question 3

what is the protein and non-protein portion of a complex enzyme known as?

Answer 3

protein portion - apo-enzyme

non-protein portion - cofactor

Question 4

what is the apo-enzyme?

Answer 4

• protein part of an enzyme without any cofactors or prosthetic group that may be required for the enzyme to be functional
• catalytically inactive

Question 5

what is the cofactor?

Answer 5

• may be a metal ion - iron, magnesium, zinc or calcium
• may be an organic molecule - known as coenzyme which are derived from vitamins

Question 6

what do the apo-enzyme and the cofactor form?

Answer 6

a catalytically active enzyme known as a holoenzyme

Question 7

what is a prosthetic group?

Answer 7

a coenzyme or metal ion that is covalently bound to the enzyme protein

Question 8

give examples of enzymes and the chemical reactions they catalyse?

Answer 8

• oxidases add oxygen
• kinases add phosphate
• dehydrogenases remove hydrogen
• ATPases split ATP
• proteases break down proteins
• lipases break down lipids

Question 9

what is the function of ribozyme?

Answer 9

• catalyses covalent changes in structure of RNA molecules
• removes parts of larger RNA molecule and splices remaining parts together to form the functional RNA molecule

Question 10

what is activation energy?

Answer 10

the level that must be reached for reactants to react and produce products

Question 11

how do enzymes affect activation energy?

Answer 11

as they increase the rate of reaction they reduce the amount of activation energy required to get the substrate molecules to react

Question 12

what does the association of the substrate with an enzyme create?

Answer 12

a new energy profile for the reaction, with a lower energy of activation

Question 13

what is formed when an enzyme and substrate react together?

Answer 13

enzyme-substrate complex

Question 14

what is the active site?

Answer 14

the region of an enzyme that binds the substrate to form the enzyme-substrate complex and transform it into a product

Question 15

describe features of the active site that are important

Answer 15

• it is a 3D cleft/crevice on the surface
• non-polar environment
• it is between 3-12 amino acids long (rest help maintain shape)
• size and shape are complementary to substrate
• active site holds substrate by combination of many weak non-covalent bonds eg. H bonds, VDWFS, electrostatic interactions and hydrophobic interactions

Question 16

describe the lock and key model for substrate binding

Answer 16

shape of active site on enzyme and its corresponding shape on substrate are considered to be rigid and fixed and perfectly complement each other when the two shapes are in the correct alignment

Question 17

deserve the induced fit model for substrate binding

Answer 17

• active site/ substrate are approximately complementary
• once substrate binds to active site, active site becomes modified to the exact complementary shape
• bonds in enzyme-substrate complex are under stress as the enzyme is not in natural conformation
• stress on bonds that lowers activation energy required for reaction to proceed

Question 18

how does temperature affect enzyme activity?

Answer 18

• as temperature increases, kinetic energy of the enzyme and substrate will increase leading to an increase in rate of chemical reaction
• above a certain temperature, enzymes will rapidly denature, leading to the loss of its 3D structure and a change in the precise shape of the active site
• means substrate can no longer bind as efficiently and therefore catalytic properties are lost

Question 19

how does pH affect enzyme activity?

Answer 19

• changes in pH affect the charge on the side chains of the amino acids making up the enzyme
• altering charge affects the bonds that can form and so affects the overall shape of the enzyme molecule and in turn affects the formation of the enzyme-substrate complex

Question 20

describe how irreversible inhibitors work and give examples

Answer 20

• they bind tightly via covalent bonds to the active site of the enzyme molecule so that it loses its catalytic properties
• eg. cyanide and penicillin

Question 21

describe how reversible inhibitors work

Answer 21

bind to enzyme via weak non-covalent bonds which are rapidly formed and easily broken

Question 22

what are the two types of reversible inhibitors?

Answer 22

competitive and non- competitive

Question 23

where do competitive inhibitors bind?

Answer 23

at the active site

Question 24

where do non-competitive inhibitors bind?

Answer 24

at a site other than the active site

Question 25

what effect does a non-competitive inhibitor have on an enzyme?

Answer 25

- causes a change in the overall 3D shape of the enzyme including the shape of the active site - leads to decreased affinity of the substrate for the enzyme -decreases catalytic activity of the enzyme