Making Life Possible II - Energy Generation and Metabolism

Question 1

Energy and Entropy

Answer 1

Entropy means disorder, randomness, uncertainty
First law: ‘Energy can neither be created nor be destroyed, it can only be transferred from one form to another’
Second law: ‘The entropy of any isolated system always increases’.

Question 2

How do living systems maintain low entropy?

Answer 2

Entropy tends to increase with time. A living system maintains low entropy by being open to flows of energy and mass.

Question 3

Gibbs Free Energy (Delta G)

Answer 3

Delta G (units kJ/mol) is a thermodynamic potential reflecting the maximum amount of work performable (available energy) by a thermodynamically closed system at a constant temperature and pressure.
Actual delta G is a function of standard delta G^0 and the actual concentrations of reactants.
Three cases:
Equilibrium reaction delta G = 0
Exergonic reaction delta G is negative, products have less free energy than reactants, free energy released. Reaction can proceed forward.
Endergonic reaction delta G is positive, products have more free energy than reactants, free energy is required for reaction to proceed forward.

Question 4

Delta G^0 equation

Answer 4

Delta G^0 = -RT ln Keq (equilibrium constant)

Question 5

Equilibrium constant (Keq)

Answer 5

[Product]/[Substrate] ignoring stoichiometry

Question 6

Le Chatelier’s principle

Answer 6

Le Chatelier’s principle - a system responds to perturbation by acting to alleviate it.

Question 7

Metabolic energy (delta G) uses

Answer 7

• Ion transport, creating transmembrane potential gradients, allowing impulse propagation
  
  • Mechanical force: actomyosin (muscle), kinesin & dyneins (microtubules: organelles, flagella)
  • Chemical synthesis (anabolism)
    Others e.g. bioluminescence

Question 8

How is Energy supplied?

Answer 8

At the point of use, energy is almost invariably supplied by ATP hydrolysis
ATP is made by processes of catabolism.
ATP/ADP system is thereby an intermediary, an ‘energy currency’.

Question 9

Gibbs Free Energy (Delta G)

Answer 9

Delta G (units kJ/mol) is a thermodynamic potential reflecting the maximum amount of work performable (available energy) by a thermodynamically closed system at a constant temperature and pressure.
Actual delta G is a function of standard delta G^0 and the actual concentrations of reactants.
Three cases:
Equilibrium reaction delta G = 0
Exergonic reaction delta G is negative, products have less free energy than reactants, free energy released. Reaction can proceed forward.
Endergonic reaction delta G is positive, products have more free energy than reactants, free energy is required for reaction to proceed forward.

Question 10

ATP supply and use

Answer 10

Gibbs free energy of ATP hydrolysis (delta G) determines energy available per ATP, and is an important regulatory signal.
Variations in delta G (ATP) can be an important metabolic signal, it cannot be allowed to vary too much.

Question 11

Creatine Kinase

Answer 11

Note: Creatine kinase, in e.g. muscle and brain, ‘buffers’ temporary mismatch of ATP supply and demand.

Question 12

Ways of producing glucose

Answer 12

Substrate Level Phosphorylation
Oxidative Phosphorylation

Question 13

Substrate Level Phosphorylation

Answer 13

Substrate level phosphorylation - uses ADP and a phosphate-containing substrate e.g. PEP or ADP.
PEP + ADP <-> Pyruvate + ATP (Pyruvate kinase)
2ADP <-> ATP + AMP (adenylate kinase)

Question 14

Metabolism

Answer 14

Anabolism + Catabolism = Metabolism
Catabolism is the breaking down of molecules which provides energy.
Anabolism is the synthesis of molecules which uses energy.

Question 15

Catabolism: Glucose

Answer 15

Glycolysis:
Redox stoichiometry - Generates 2 NADH, either reduce pyruvate to lactate, or oxidised in electron transport chain (ETC).
ATP Stoichiometry - uses 2 ATP, generates 2 x 2 ATP so net yield = 2 ATP (Extra p from 2 Pi)

Question 16

Fates of Pyruvate

Answer 16

Anaerobic conditions: Lactate (human), ethanol (yeast)
Fed state: Cellular respiration, via Acetyl CoA, the TCA cycle and oxidative phosphorylation
Fasting state: Gluconeogenesis via oxaloacetate
Also transamination, to amino acids.

Question 17

Tricarboxylic Acid Cycle

Answer 17

= Krebs cycle = Citric acid cycle
Cycle of chemical reaction that oxidises acetyl CoA derived from carbohydrates, fats or proteins.
Produces 1 GTP directly, but most ‘oxidative’ ATP comes from oxidation of 3 NADH and 1 FADH2 via oxidative phosphorylation.

Question 18

Oxidative Phosphorylation

Answer 18

Electron transport chain (ETC) = Respiratory Transport Chain
Located in the inner mitochondrial membrane
A series of components that oxidise reducing equivalents and use the energy to make ATP.

Question 19

Electron Transport Chain

Answer 19

In the mitochondrion, a series of linked reactions couple the oxidation of NADH and FADH2 with the transfer of electrons and pumping of H+ ions into the intermembrane space, the resulting gradient drives ATP synthesis.
Here the coupling between exergonic substrate oxidation and endergonic ATP synthesis is a transmembrane H+ gradient.
ATP synthesis is driven by the chemiosmotic movement of H+ down this gradient.

Question 20

Stoichiometry

Answer 20

Stoichiometry = ratios between quantities of reactants and products