Bioenergetics

Question 1

Define: Entropy

Answer 1

the degree of disorder in a system and the entropy of a universe is always increasing (2nd Law). ΔS = + in a favorable reaction.

Question 2

Define: Enthalpy

Answer 2

pertains to the total heat content of the system (i.e. internal energy). ΔH = - in a favorable reaction (exothermic; heat is released).

Question 3

Define: Free Energy

Answer 3

Gibb’s free energy measures the favorability/usefulness of a reaction. ΔG = ΔH – TΔS. –ΔG = a favorable reaction that occurs spontaneously; reactions goes towards the products.

Question 4

Define: High Energy Compounds

Answer 4

Energy released by hydrolysis of bonds and can couple unfavorable reactions to these compounds to make them more favorable

Question 5

Types of High Energy Compounds and Their Bonds

Answer 5

High-energy compounds generally contain thioester bonds or high-energy phosphate bonds (Acetyl-Co-A, Phosphoanhydride (P-O-P, ATP), Phosphcreatinine (P-N), Phosphenolpyruvate (C-O-P))

Question 6

Redox Reactions

Answer 6

involves an exchange of electrons. LEO goes GER. Measured by reduction potential E, a measure of readiness of molecule to accept electrons. +E = readily accepts (favorable reactions have +E). –E = readily donates. ΔG = -nFΔE.

Question 7

Define: 1st Law of Thermodynamics

Answer 7

Energy is neither created nor destroyed; it takes different forms.

Question 8

Define: 2nd Law of Thermodynamics

Answer 8

Entropy is always increasing (flows to a more stable source).

Question 9

Describe Kinetic Energy

Answer 9

energy in motion. Radiant energy (sun), thermal energy (heat), mechanical energy (movement of cells and its parts), & electric energy (movement of charged particles down gradients).

Question 10

Describe Potential Energy

Answer 10

energy something has based on its position/arrangement. Stored in chemical bonds, concentration gradients, electric fields from charge separation, and redox pairs.

Question 11

ΔG = ΔG° + RTln[products]/[reactants]

Answer 11

ΔG° pertains to standard conditions. R = gas constant (1.98 cal/mol K) and T = temperature in Kelvins.

Question 12

ΔG° = -RTlnKeq

Answer 12

Keq = equilibrium constant and is [products]/[reactants]. 
ΔG° = -2.3RTlogKeq

Question 13

ΔG = ΔH – TΔS

Answer 13

used to calculate free energy/favorability. Want a -#.

Question 14

Whats the relationship between the sign of ΔG and the direction of a reaction under standard conditions.

Answer 14

Keq >1 = -ΔG = reaction goes in forward direction (to products)
Keq = 1 → ΔG = 0 → reaction is at equilibrium
Keq <1 = +ΔG = reaction goes in reverse direction (to reactants)

Question 15

Describe the effects of positive/negative entropy and enthalpy on the thermodynamic forces driving a reaction based on the equation
ΔG = ΔH – TΔS.

Answer 15

∆H = negative ∆S = positive - spontaneous at any temperature
∆H= positive ∆S = negative - not spontaneous at any temperature
Both negative, spontaneous only if T is low
Both positive, spontaneous at a high T

Question 16

What’s the numerical conversion between free energy and redox potential in biological systems?
(ΔG = -nFΔE)

Answer 16

N = # of electrons transferred. F = Faraday’s constant. ΔE = difference in reduction potential in volts = Eelectron acceptor – Eelectron donor. E is high for electronegative molecules.

Question 17

How does the oxidation of glucose generate energy?

Step by step process.

Answer 17

Harnesses energy for ATP production. Glucose donates e- & O2 is the final e- acceptor.
In electron flow → the “circuit” for e- flow = series of proteins that release energy in small steps → makes high energy compounds like NADH and NADPH that readily surrender their e- (very negative E values).

Question 18

How is ATP formed?

Answer 18

ATP is made by harnessing energy in H+ gradients and electric potential across mitochondrial inner membrane. Aided by ATP synthase, which is a mechanical device that converts energy of proton gradient to high energy phosphate bonds (uses rotational catalysts).

Question 19

What are the additive properties of free energy and how does that relate to unfavorable reactions?

Answer 19

Unfavorable reactions can occur by coupling them to favorable reactions, like the hydrolysis of a high-energy compound (like ATP). ΔG3 = ΔG1 + ΔG2

Question 20

What are the major “high energy” compounds used in biological systems and the principle of energy storage in “high-energy” bonds?”

Answer 20

Thioester C-S bond = acetyl Co-A.
Phospoanhydride P-O-P bond = ATP
P-N = phosphocreatine.
C-O-P = phosphoenolpyruvate.