Enzymes

Question 1

Enzymes Function

Answer 1

extract energy from glucose, burning hydrocarbon fuels, nitrogen fixation, digesting breakfast

Question 2

Two ways to accelerate a reaction

Answer 2

adding heat, adding a catalyst

Question 3

adding heat

Answer 3

increases the number of reactants with sufficient energy to overcome the activation energy barrier

Question 4

adding a catalyst

Answer 4

decreases the activation energy barrier nut does not react

Question 5

Enzymes as proteins

Answer 5

typically globular, structure is determined by the same forces

Question 6

enzymes as catalysts

Answer 6

accelerate reaction rates, regenerated, specific

Question 7

nomenclature

Answer 7

ending in -ase, usually describe process

Question 8

what need you need for a reaction to proceed (think in energy terms)

Answer 8

free energy of products is less then the free energy of the reactants (products less then reactants) (exergonic and spontaneous)

Question 9

reaction speed effector

Answer 9

determined by the size of the activation energy barrier

Question 10

how do enzymes effect free energy

Answer 10

reduces the free energy of the TS (NOT the free-energy change of the reaction)

Question 11

How do enzymes reduces the free energy of the transition state (4 ways)

Answer 11

1. removing substrates from aqueous solution (desolvation)
2. proximity and orientation effects
3. taking part in the reaction mechanism
4. stabilizing the TS

Question 12

active sites

Answer 12

region of enzyme where catalysis occurs. determines affinity specificity, and rate, complementary to substrate

Question 13

desolvation

Answer 13

exclusion of water

Question 14

3 desolvation advantages

Answer 14

• removal of water shell accelerates reactions
• enhances polar interactions
• prevents side reactions

Question 15

induced fit

Answer 15

some change shape when substrate binds
- close activation site
- bring catalytic reactive groups together
(like a waffle iron surrounding dough when it cooks)

Question 16

proximity and orientation

Answer 16

active sites bind close to eachother and in the right geometry (needed for reactions to occur)

Question 17

participation in reaction

Answer 17

enzymes (some) position functional groups near the substrates in the activation site (maybe function as:
acid/base catalysis
covalent catalysis
metion ion catalysis)

Question 18

AA side chains in Acid/Base catalysis

Answer 18

Asp, Glu, His, Lys,
Cys, Tyr (not usually - more so nucleophilic)

Question 19

AA side chains in Nucleophilic Catalysis (covalent catalysis)

Answer 19

Ser, Try, Cys, Lys, His
(in deprotonated form these can act as nucleophiles)

Question 20

sub groups of cofactors

Answer 20

coenzymes and metal ions

Question 21

sub groups of coenzymes

Answer 21

cosubstrates and prosthetic groups

Question 22

sub groups of metal ions

Answer 22

prosethic group and loosely bound

Question 23

Apoenzyme

Answer 23

polypeptide without the prosthetic group

Question 24

holoenzyme

Answer 24

polypeptide with the prosthetic group to form the functional tertiary structure

Question 25

transition state stabilization

Answer 25

- binding the TS aids in lowering the DG(double dagger) - parts of the protein interact with the unstable transition state - enzyme activity sites bind the TS better then the substrate

Question 26

tighter enzyme binding with TS

Answer 26

greater catalytic activity

Question 27

regulation of enzyme activity (effect intrinsic activity)

Answer 27

competitive inhibiton, allostery, reversible covalent modification, ionic signals

Question 28

regulation of enzyme activity (do not effect the intrinsic activity)

Answer 28

regulation of gene expression, changes in subcellular localization

Question 29

competitive inhibitors

Answer 29

- bind reversibly in the activation site - resemble TS or substrate but do not react - physically blocks activation site (fewer sites available, lowers reaction rate)

Question 30

how can you get over the decrease in reaction rate of competitive inhibitors

Answer 30

increase substrate concentration

Question 31

allosteric enzymes

Answer 31

mulit subunit activity may be cooperative

Question 32

stabilize T - state

Answer 32

inhibitor

Question 33

stabilize R state

Answer 33

activator

Question 34

covalent modification of AA residue

Answer 34

changes the tertiary structure of a polypeptide (effect affinity) (phosphorylation is a great example)