Week 7-8

Question 1

METABOLISM

• Metabolism
• Catabolism
• Anabolism

Answer 1

Metabolism: break down

• Metabolic reactions involve energy changes
• Energy is the capacity to do work/ capacity for change
• Energy changes are usually associated with changes in chemical composition
• Chemical energy is stored in bonds

Catabolism: break down

• Involves the breakdown of complex macromolecules
• Causes release of energy stored in chemical bonds
• Occurs via oxidative pathways
• Released energy can be recaptured in new chemical bonds or used as kinetic energy

Anabolism: build up

• Uses precursors (small molecules) to synthesize complex macromolecules
• Requires energy input
• Energy is captured in the chemical bonds and stored as potential energy

1. Large molecules broken down in CATABOLIC reactions and are oxidised to produce electrons
2. Eventually broken down into precursors (CO2, H2O, NH3)
3. These precursors are used to synthesize larger molecules in ANABOLIC reactions, where electrons are used as energy
4. Hence the reactants are reduced (reductive synthesis)
5. Cycle repeats

Question 2

METABOLISM

• Laws of Thermodynamics
• Entropy

Answer 2

1st Law of Thermodynamics:
Energy is neither created or destroyed

2nd Law of Thermodynamics:
When energy is converted from one form to another, some energy is lost due to disorder (entropy)

Entropy:

• Entropy is the disorder in system
• It takes energy to impose order on a system
• Unless energy is applied to a system, it will be randomly arranged/disordered

Question 3

METABOLISM

- Energy conversions

Answer 3

• In a cell, you have both exogenic and endogenic reactions
• Exogenic provide the necessary energy for endogenic reactions to occur

ΔG = ΔH - TΔS
where ΔG = free energy/usable energy
(exogenic -ve, endogenic +ve)
(G = 0, system = equilibrium)
ΔH = total energy (enthalpy)
T = absolute temperature
ΔS = usable energy (entropy)

Question 4

METABOLISM

- ATP

Answer 4

• In all metabolism, the final objective is to gain ATP
• ATP = adenosine triphosphate
• Consists of 3 phosphate groups, a sugar, and an adenosine nucleotide
• It is a high energy molecule
• ATP has 4 -ve charges in proximity, hence there is a strong electron repulsion
• When hydrolysised for the first time, the first phosphate group will break off, forming adenosine diphosphate
  (less for 2nd time, forming adenosine monophosphate)
  (adenosine is made up of sugar+adenosine nucleotide)
• Energy released is directly proportional to the charge repulsion felt by the molecule
• This is the energy used to power ENDOGENIC reactions

Question 5

METABOLISM

- 5 principles that govern metabolic pathways

Answer 5

1. Complex chemical reactions occur as a series of separate pathways
2. Each reaction is catalysed by a specific enzyme
3. Many metabolic pathways are similar in all organisms
4. Key enzymes can be inhibited or activated to alter the rate of the pathway
5. In eukaryotes, metabolic pathways are compartmentalised n specific organelles