Bioenergetics

Question 1

Define entropy (S)

Answer 1

measure of the randomness or disorder of a chemical system

Question 2

What does a Positive (+) ∆S indicate?

Answer 2

increase in entropy measured as an increase in randomness

Question 3

What are the units of entropy?

Answer 3

Units: joules/mole x Kelvin= J/m xK = J/molxK

Question 4

Give an example of entropy

Answer 4

Ex 1) irreversible loss of heat from tea kettle to kitchen
Ex 2) oxidation of glucose (1 glucose + 6 O2 -> 6CO2 +6H2O) 7 molecules to 12 molecules: anytime chemical rxn increases # of molecules, solid -> liquid, liquid -> gas => entropy increases
Ex 3) information as energy (words/ passages have meaning, scrambled letters do not) information is “negative entropy”

Question 5

Define enthalpy (H)

Answer 5

reflects the heat content of a reacting system
- A measure of the total thermodynamic energy in a system including:
Number and kinds of chemical bonds in reactants and products
Thermodynamic potential
Volume & pressure

Question 6

What is the ∆H of a system?

Answer 6

∆H system = ∑ of non-mechanical work done on it & heat supplied to it

Question 7

What does (+)∆H indicate?

Answer 7

(+)∆H = endothermic reaction (take up heat)

Question 8

What does ( -) ∆H indicate?

Answer 8

( -) ∆H = exothermic reaction (release heat)

Question 9

What are the units of entropy (H)

Answer 9

Units: joules/ mole = J/m or calories/ mole (1 cal = 4.184J)

Question 10

What is free energy? (G)

Answer 10

the maximum amount of non-expansion work that can be extracted from a closed system

∆G = chemical potential that is minimized when a system reaches equilibrium at constant pressure and temperature => appropriate measure of spontaneity of process occurring at constant pressure and temperature

Question 11

What are the units of G?

Answer 11

Units: joules/ mole = J/m or calories/mole (1 cal = 4.184J)

Question 12

What does Negative ( - ) ∆G indicate?

Answer 12

Negative ( - ) ∆G = spontaneous

Question 13

What does Positive ( + ) ∆G indicate?

Answer 13

Positive ( + ) ∆G = non-spontaneous

Question 14

What is an endergonic reaction?

Answer 14

Endergonic reaction is energy requiring

Question 15

What is an exergonic reaction?

Answer 15

Exergonic reaction is energy releasing

Question 16

How do cells complete energetically unfavorable reactions?

Answer 16

Cells rely on molecules (proteins/ nucleic acids) with +∆G -> to complete the thermodynamically unfavorable reactions (endergonic), cells couple them with favorable (exergonic) reactions (often E released by hydrolysis of phosphoanhydride bonds of ATP)

Question 17

What does the reduction potential (E) measure ?

Answer 17

readiness of molecule/ atom to accept e- compared to H+
more +E = more likes to accept e-
more –E = more likes to donate e-

Question 18

How are metabolic fuels (carbohydrates/ fats) used to complete cellular work?

Answer 18

they are oxidized

Question 19

How does O2’s high affinity for e- drive ATP synthesis?

Answer 19

O2’s high e- affinity mean e- transfer process is exergonic, energy is released to drive ATP synthesis (the goal of catabolism)

Question 20

Describe the forms of kinetic energy

Answer 20

Radiant energy: photons from sun (ultimate source of all E in living systems)

Thermal energy: (temperature) protein molecules function optimally at a particular temperature or need certain thermal E to function

Mechanical energy: movement of cells and cell components

Electrical energy: movement of charged particles down gradients of electric potential

Question 21

Describe the forms of potential energy

Answer 21

Stored in chemical bonds
Stored in concentration gradients
Stored in electric fields from charge separation
Stored in redox pairs

Question 22

What is the equation for Keq?

Answer 22

keq = ([products]^#molecules of product)/ ([reactants]^# molecules of reactants)

Question 23

If Keq is >1.0, what is ∆G and how does the reaction proceed?

Answer 23

∆G is negative

rxn proceeds forward

Question 24

If Keq is <1.0, what is ∆G and how does the reaction proceed?

Answer 24

∆G is positive

rxn proceeds in reverse

Question 25

If Keq =1.0, what is ∆G and how does the reaction proceed?

Answer 25

∆G is zero

rxn is at equilibrium

Question 26

What is the equation for the change in Gibbs free energy for a reaction (∆G)?

Answer 26

ΔG = ΔH - T ΔS

Question 27

How does ∆G relate to Keq?

Answer 27

ΔG =G0 + RT ln [PRODUCTS]/[REACTANTS]
Keq = [products]/[reactants]

ΔG0 = - RT lnK

Question 28

What is the conversion between ∆G and ΔE?

Answer 28

ΔG = -nFΔE
n = # of e- transferred
F = faraday constant (96,500 joules/voltmol) – magnitude of electric charge per mole of e-
∆E = difference in reduction potential in volts, e- acceptor- e-donor

Question 29

Are ∆G’s for a series of reactions additive or independent?

Answer 29

Standard free energy changes for a set of reactions are additive.
Free energy changes for multiple reactions can be coupled to overcome activation energy required to begin reaction
In this way a reaction with a net increase of S, but high activation E can proceed