L4

Question 1

equilibrium constant

Answer 1

K = [AB]/[A] x [B] at equilibrium

AB = product
A, B = reactants

Question 2

how does concentration of reactants impact if a rxn will proceed

Answer 2

1. if low or no A or B - wont proceed; equilibrium tends to shift left
2. if high A or B - will proceed; equilibrium tends to shift right

Question 3

how does concentration of products impact if a rxn will proceed

Answer 3

1. if high AB - wont proceed b/c equilibrium shifts left
2. if low AB - will proceed, equilibrium shifts to the right

Question 4

thermodynamic influence on a reaction

Answer 4

negative delta G = spontanrous, requires no energy input (Active transport) - more energy in substrates than in products

positive delta G = not spontaneous, require energy input to proceed (ATP production) - more energy in products than in substrates

Question 5

if some rxns are spontaneous what keeps them from occurring continuously? - ask tutor slide 8

Answer 5

transition state: unstable, high energy, thermodynamically unfavorable

reactants dont go there, delta G high; they tend to return to lower delta G state

activation energy - a barrier for a spontaneous rxn

Question 6

enzymes speed up rxns by…

Answer 6

reducing activation energy

Question 7

enzymes are proteins or riboproteins

Answer 7

Do the work of metabolism: the totality of an organism’s chemical reactions

A metabolic pathway begins with a specific molecule and ends with a product

Each step is catalyzed by a specific enzyme

Question 8

how do enzymes lower activation energy of reactions?

Answer 8

3D structure of protein has “Active site” that binds substrates

1. creates high local concentration of substrates
2. holds them in a precise orientation that facilitates bonding
3. allows substrates to persist in the transition state

Question 9

what happens at the active site?

Answer 9

lysozyme cleaves a polysaccharide - degrades sugar polymers

Question 10

induced fit model (HK) - ask tutor

Answer 10

specific example: Hexose Kinase, an enzyme in glycolysis, initiates reactions that make more ATP in cells

induced fit:
substrate binds enzyme, changing shape of enzyme…

…and the enzyme changes the shape of the bound substrate, putting strain into the substrate

Shape change of the enzyme brings active site amino acids together that together catalyze the rxn

strained swubstrate is susceptible to react at the active site

Question 11

feedback inhibition

Answer 11

Glucose and ATP (reactants, shown as red hexagon) binds to hexose kinase at
active site.

• Glucose-6-phospate (product, shown as yellow keyhole, labeled molecule X) forms.
• Accumulating G6P binds elsewhere on hexose kinase and reduces its activity.
• Other metabolites (not just the reaction product) can inhibit enzymes.

Question 12

positive regulation

Answer 12

Phosphofructokinase (PFK): Another enzyme in glycolysis controls a reaction subsequent
to (i.e. downstream of) the one controlled by hexokinase

• Subject to positive regulation
• When ATP levels are low, its degradation product, AMP (green arrowhead, labeled
  molecule X), is high
• AMP stimulates PFK activity, which can lead to more ATP production.

Question 13

allosteric regulation of enzymes - ask tutor

Answer 13

both feedback inhibition and positive regulation are examples of this (using other sites besides Active Sites for binding events)

Question 14

pharmacologic regulation of enzymes

Answer 14

competitive inhibitors bind to the ACTIVE site of an enzyme, competing with the substrate

noncompetitive inhibitors bind to an ALLOSTERIC site of an enzyme, causing a change in shape and making the active site less effective

Question 15

how do you make a rxn w a positive delta G go?

Answer 15

coupling the rxn w a reaction with a higher negative delta G; net delta G is negative for both. rxns: a spontaneous coupled reaction

Question 16

enzymes are often in complexes

Answer 16

enables reaction intermediates to be passed between enzymes sequentially

Question 17

enzymes have optimal conditions