Bioenergetics

Question 1

Isolated System -

Answer 1

• Cannot exchange energy or matter with its surroundings

Question 2

closed system

Answer 2

can exchange energy heat or work

Question 3

open

Answer 3

can exchange both energy and matter

Question 4

First law of thermodynamics

Answer 4

Energy can neither be created nor destroyed

but it can be changed from one form to another or transported from one region to another

Question 5

Explanation of 1st law

Answer 5

• Deals with energy balance in a reaction but doesn’t say anything about the preferred direction of the reaction
• Energy before = energy after

Question 6

The heat change of a reaction at constant pressure = the enthalpy change

Answer 6

^H = ^U + P^V

Question 7

2nd law

Answer 7

Any spontaneous process must cause
the entropy of the Universe to increase:
DSsystem + DSsurroundings = DSUniverse > 0

Question 8

Entropy (S) is

Answer 8

A state function that

measures the degree of disorder or randomness of a system

Question 9

2nd law equation and explaination

Answer 9

S = K loge W

• K = boltman constant
• W = ways of arranging system
• 2nd law : Spon change occurs in a direction that increases the combined entropy and the system and surroundings

Question 10

Gibbs free energy

Answer 10

• The general condition for a process to occur spontaneously at constant temperature and pressure is
  ^G = ^H -T^S
  Temp in kelvin

Question 11

Value of delta G related to favourability

Answer 11

Delta G > 0 unfavourable – endergonic
Delta G = 0 equilibrium
Delta G < 0 favourable – exergonic

Question 12

Gibbs free energy, G, is at what value at equilibrium??

Answer 12

minimum at equilibrium

Question 13

What does ^G indicate?

Answer 13

indicates the thermodynamically preferred direction of a reaction, but not the rate at which the reaction proceeds

Question 14

What determines the favourable direction?

Answer 14

For all chemical and physical processes, the interplay between DH and TDS

Question 15

Factors that affect ^G

Answer 15

1. Alter concentrations

2. Couple reactions

Question 16

When all concentrations are 1 M

Answer 16

^G = ^G0

Question 17

Key equation 3

Answer 17

DGº = –RT ln Keq

Question 18

Key Equation 2

Answer 18

^G = ^G + RT loge [C]c[D]d / [A]a[B]b

Question 19

What properties of ATP make it the major energy currency of biochemical processes?

Answer 19

• Relatively negative DG of ATP hydrolysis due to highly charged ATP polyphosphate group:
• relief of electrostatic repulsion
  when terminal phosphate bond is
  hydrolysed;
• inorganic phosphate (Pi) undergoes
  stabilisation as a resonance hybrid.

Question 20

What properties of ATP make it the major energy currency of biochemical processes?

Answer 20

• ATP is thermodynamically unstable but kinetically stable – ATP hydrolysis has a high activation energy (200 to 400 kJ mol-1)
• Specific enzymes are required to catalyse phosphoryl group transfer
• The cell can therefore regulate the distribution of energy carried by ATP by regulating enzymes that act on ATP

Question 21

With thermodynamics, one cannot determine

Answer 21

the speed of a reaction.