CH 6 - enzymes

Question 1

enzymes

Answer 1

protein catalysts

speed up slow endergonic reactions

lower activation energy

Question 2

activation energy

Answer 2

energy necessary to reach the transition state

Question 3

catalysts

Answer 3

increase reaction rate but are neither products nor reactants

Question 4

catalytic cycle (see Fig 6-7, p.138)

Answer 4

1. Enzymes bind to one or more reactants.
2. Some residues are commonly found on active sites.
3. May include cofactor which is either metal ion or organic/coenzyme.
4. Binding involves some specificity.

Question 5

substrate

Answer 5

molecule upon which an enzyme acts

Question 6

active site

Answer 6

enzyme’s binding site

Question 7

specificity

Answer 7

=ability to discriminate between very similar molecules

first described as LOCK & KEY, now we see it as INDUCED FIT

Question 8

induced fit

Answer 8

binding distorts the shape of the enzyme and substrate

evidence comes from x-ray crystallography (x-ray diffraction)

Question 9

reducing activation energy involves:

Answer 9

1. stressing certain bonds

2. donating or accepting protons or electrons

Question 10

direction of a reaction

Answer 10

• -determined by deltaG

- -enzymes do not affect deltaG therefore enzymes catalyze reverse reactions as well as forward ones

Question 11

enzyme naming

Answer 11

usually ends in -ase

sometimes named for substrate

sometimes named for reaction

enzyme class system - based on six classes that get subdivided

Question 12

oxireductases

Answer 12

oxidation-reduction reactions

Question 13

transferases

Answer 13

transfer of functional groups from one molecule to another

Question 14

hydrolases

Answer 14

hydrolytic cleavage of one molecule into two molecules

Question 15

lyases

Answer 15

removal of a group from, or addition of a group to, a molecule with rearrangement of electrons

Question 16

isomerases

Answer 16

movement of a functional group within a molecule

Question 17

ligases

Answer 17

joining of two molecules to form a single molecule

Question 18

units for reaction rate

Answer 18

mol/(L*sec) or (mol/L)/sec

Question 19

reaction rate

Answer 19

=change in specific quantity/change in time

slope on graph of position (m) vs. time (s)

Question 20

what does slope (on position vs time graph) represent?

Answer 20

reaction rate!

negative slope = running out of reactants; decrease [reactants] increase [products]

positive slope = increase [reactants] decrease [products]

straight/same slope = equilibrium

Question 21

enzyme kinetics

Answer 21

=study of enzyme activity and what affects it

focus on initial reaction rates

Question 22

effect of substrate concentration on velocity

Answer 22

increase [substrate] = increased velocity

Question 23

saturation

Answer 23

=the inability of higher substrate concentrations to increase the reaction rate beyond a finite upper value

Question 24

Vmax

Answer 24

maximum reaction rate

velocity at saturating substrate concentrations

Question 25

Km

Answer 25

substrate concentration that gives you half of Vmax

Question 26

Michaelis-Menten equation

Answer 26

v=(Vmax*[S])/(Km + [S})

Question 27

what happens if [S] is much higher than Km?

Answer 27

at very high [S], velocity of reaction is essentially independent of variation in [S] and is approximately constant at Vmax v=Vmax

Question 28

what happens if [S] is much lower than Km?

Answer 28

at very low [S], initial velocity is roughly proportional to [S] v=(Vmax*[S])/Km

Question 29

zero order reaction

Answer 29

when a reaction rate is independent of the concentration of the reactants

Question 30

first order reaction

Answer 30

a reaction that depends on reactant concentration in a simple, straightforward way

Question 31

enzyme activity is dependent on what factors?

Answer 31

temperature and pH

Question 32

effect of temperature on enzyme activity

Answer 32

below optimal temperature: rate of enzyme-catalyzed reaction increases with temperature (positive slope) above optimal temperature: enzyme is rapidly inactivated by denaturation (negative slope)

Question 33

pH sensitivity due to:

Answer 33

1. residues at the active site that must be at the right pH to carry the right charges to be neutral 2. sometimes the substrate has components whose charge is determined by pH 3. tertiary structure involves ionic bonds; the residue must be ionized

Question 34

enzyme inhibition (Fig 6-14, p. 145)

Answer 34

can be competitive or non-competitive

Question 35

competitive inhibitors

Answer 35

compete with the substrate for the active site increases Km: increases [S] required to approach Vmax same effect as reducing [S]

Question 36

noncompetitive inhibitors

Answer 36

same effect as reducing enzyme concentration reduces Vmax

Question 37

two major mechanisms of enzyme regulation

Answer 37

allosteric regulation | covalent modification

Question 38

allosteric effector (Fig 6-15, p. 147)

Answer 38

small, organic molecule that regulates the activity of an enzyme for which it is not the substrate nor the immediate product

Question 39

allosteric regulators

Answer 39

bind the enzyme away from the active site

Question 40

are allosteric inhibitors competitive or noncompetitive?

Answer 40

non-competitive (Fig 6-16, p.148)

Question 41

covalent modification

Answer 41

addition or removal of specific chemical groups via covalent bonding Ex: phosphorylation

Question 42

phosphorylation

Answer 42

addition of a phosphate group most commonly by transfer of phosphate group from ATP to hydroxyl group of a serine, threonine, or tyrosine residue in the protein

Question 43

protein kinases

Answer 43

phosphorylating enzymes that transfer the phosphate from ATP

Question 44

protein phosphatases

Answer 44

enzymes that remove phosphates from a phosphorylated protein

Question 45

zymogen

Answer 45

inactive enzyme precursor some enzymes are activated by hydrolysis of zymogen