Biochem 244 Objectives

Biochemistry 244 Sample answers to Objective Questions

Please send your queries, comments and corrections to jendeb@sun.ac.za

Theme A: Energetics of Life

2. Schematically represent and briefly discuss the flow of energy and matter through the biosphere

[pic]

3. Describe living systems as thermodynamic systems

Living systems are open systems, so energy and matter can flow through the system. Therefore energy and concentrations of matter change in the system. Pressure, volume and temperature remain fairly constant in the system.

4. Name the most important thermodynamic variables in living systems

Pressure, volume, temperature: tend to remain constant, or only small fluctuations.

Energy, concentrations of metabolites/matter: fluctuate widely.

5. Give the relationships between ∆G or ∆G’ and the direction of a reaction under the following conditions:

a) ∆G < 0

If ∆G is negative, then the reaction is spontaneous in the direction it is written (left to right). There is free energy waiting to be released when the reaction occurs left to right.

b) ∆G>0

If ∆G is positive, then the reaction is not spontaneous in the direction it is written (left to right). Energy must be ADDED to have the reaction go from left to right. Therefore the reaction will proceed spontaneously from right to left.

c) ∆G = 0

If ∆G = 0, the reaction is already at equilibrium. There is no release of free energy if the reaction proceeds in either direction. Therefore there will be no net movement in either direction.

6. a) Write the mathematical relationship between the Gibbs energy change (∆G), the mass action ratio (Γ) and the equilibrium constant (Keq).

∆G = RT ln (Γ/Keq)

= RT ln Γ + ∆Go

6. b) Use these relationships to explain how ∆G changes as Γ/Keq changes from 0 to ∞ (infinity)

|Γ |[R] vs [P] |Γ/Keq |ln (Γ/Keq) |∆G |

|0...