Enzymes

Question 1

Do enzymes impact the thermodynamics of a biological reaction?

Answer 1

No, delta H_rxn and the equilibrium position do not change

Question 2

What do enzymes do?

Answer 2

1. Lower the activation energy
2. Increase the rate of the reaction
3. Are not changed or consumed in the reaction (will appear in the reactants and the products)
4. Are pH and temperature sensitive, optimal activity at specific pH ranges and temperatures
5. Do not affect the overall deltaG of the reaction
6. Are specific for a particular reaction or class of reactions

Question 3

Oxidoreductases?

Answer 3

Catalyze oxidation-reduction reactions, transfer electrons between biological molecules, often have cofactors that serve as electron carriers, like NAD+ or NADP+; electron donor = reductant; electron acceptor = oxidant

Question 4

transferases?

Answer 4

catalyze the movement of a functional group from one molecule to another, ex. kinases

Question 5

kinases?

Answer 5

catalyze the transfer a phosphate group, generally from ATP, to another molecule

Question 6

Hydrolases?

Answer 6

Catalyze the breaking down of a compound into two molecules using the addition of water, ex. phosphatase, cleaves a phosphate group from another molecule

Question 7

Lyases?

Answer 7

Catalyze the cleavage of a single molecule into two products, don’t require water, don’t act as oxidoreductases, can also catalyze the reversal (two molecules into a single molecule), in that case would be called a synthase

Question 8

LIL’HOT

Answer 8

Major enzyme classifications

1. Ligase
2. Isomerase
3. Lyase
4. Hydrolase
5. Oxidoreductase
6. Transferase

Question 9

Isomerases?

Answer 9

Catalyze the rearrangement of bonds within a molecule, can catalyze reactions between stereoisomers as well as constitutional isomers

Question 10

Ligase?

Answer 10

Catalyze addition or synthesis reactions, generally between large similar molecules and often require ATP, often with nucleic acid synthesis and repair on Test Day

Question 11

Endergonic reaction?

Answer 11

One that requires energy input, deltaG>0

Question 12

Exergonic reaction?

Answer 12

One where energy is given off, deltaG< 0

Question 13

If a reaction is spontaneous, deltaG is

Answer 13

negative

Question 14

How do catalysts impact activation energy?

Answer 14

They lower it

Question 15

The molecule upon which an enzyme acts is known as its…?

Answer 15

Substrate

Question 16

The location where the substrate is held during its chemical reaction is known as the

Answer 16

active site

Question 17

Lock and Key Model

Answer 17

suggests that the enzyme’s active site is already in an appropriate conformation for the substrate (key) to bind

Question 18

Induced Fit Model

Answer 18

More scientifically accepted theory, substrate and enzyme active site don’t seem to fit, but then they do

Question 19

Enzymes without their cofactors are called

Answer 19

apoenzymes

Question 20

Enzymes with cofactors are called…

Answer 20

holoenzymes

Question 21

Tightly bound cofactors or coenzymes that are necessary for enzyme function are called…

Answer 21

prosthetic groups

Question 22

A rate of reaction can’t go faster once it has reached

Answer 22

Saturation, max velocity= v_max

Question 23

What does K_m represent?

Answer 23

The substrate concentration at which half of the enzyme’s sites are full, 1/2 V_max

Question 24

cofactors

Answer 24

small, metal cations

Question 25

coenzymes

Answer 25

small, organic molecules

Question 26

temp. impact on enzymatic reactions?

Answer 26

tend to double in velocity for every 10 degrees C, eventually will denature at higher temps

Question 27

pH impact on enzymatic reactions?

Answer 27

body works best at certain pHs

Question 28

salinity impact on enzymatic pHs?

Answer 28

altering the concentration of salt can change enzyme activity in vitro, can change conformation of the enzyme, sometimes cause denaturation

Question 29

negative feedback

Answer 29

helps maintain homeostasis, once we have enough of a given product, we turn off the pathway that created that product

Question 30

feed-forward regulation

Answer 30

enzymes may be regulated by intermediates that precede the enzyme in the pathway

Question 31

competitive inhibition?

Answer 31

involves occupancy of the active site, doesn't alter V_max, because if enough substrate is added, it will outcompete the inhibitor and be able to run the reaction at max velocity, K_m increases

Question 32

noncompetitive inhibitors?

Answer 32

bind to an allosteric site instead of the active site, which induces a change in enzyme conformation, decreases V_max, doesn't change Km

Question 33

Mixed inhibition?

Answer 33

inhibitor can bind to enzyme or the enzyme-substrate complex, different affinity for each, bind at the allosteric site, decrease V_max, can increase or decrease Km

Question 34

Uncompetitive inhibtion?

Answer 34

bind only to the enzyme-substrate complex, decrease Km and decrease vmax

Question 35

allosteric activator?

Answer 35

an activator will result in a shift that will make the active site more available for binding to the substrate by binding to the allosteric site

Question 36

allosteric inhibitor?

Answer 36

will make the active site less available for binding to the substrate by binding to the allosteric site

Question 37

allosteric sites

Answer 37

a site that can regulate the availability of the active site that's not the active site

Question 38

Glycosylation

Answer 38

the covalent attachment of sugar moieties, another covalent enzyme modification

Question 39

enzyme can be activated or deactivated by...

Answer 39

phosphorylation or dephosphorylation (covalent modification with phosphate)

Question 40

zymogens

Answer 40

inactive forms of enzymes (like ones for the stomach), often have the suffix -ogen

Question 41

irreversible inhibtion

Answer 41

alters the enzyme in such a way that the active site is unavailable for a prolonged duration or permanently; new enzyme must be synthesized for the reaction to occur again

Question 42

cooperative enzymes

Answer 42

display a sigmoidal curve bc of the change in activity with substrate binding