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Summary of Metabolism lecture series
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Notes are the summary of the Metabolism lecture series for MCB2021F
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Metabolism:Greek meaning chemical changes, raw materials/ nutrients to energy and complex product
of cells
Metabolic diversity – classifications of organisms by energy and carbon source
Chemotrophs:
1. Chemoautotrophs
- Energy source is chemical
- Carbon source is inorganic
- Examples, hydrogen-, sulfur-, iron-, nitrogen- and carbon monoxide-oxidizing
bacteria
2. Chemoheterotrophs
- Energy source is chemical
- Carbon source is organic compounds
- Examples, all animals, most fungi, protozoa and bacteria
Phototrophs:
1. Photoautotrophs
- Energy source is light
- Carbon source is inorganic
- Examples, all plants, algae, cyanobacteria and green and purple sulfur bacteria
2. Photoheterotrophs
- Energy source is light
- Carbon source is organic compounds
- Examples, green and purple non-sulfur bacteria and heliobacteria
Anabolism and Catabolism: energy is generated by catabolism and is used for anabolism
Catabolism-
- Energy generating process, breaks down/ degradation of complex molecules and
is oxidative
Anabolism-
- Energy requiring process, synthetic process which produces complex molecules
and is reductive
Molecules that link catabolism and anabolism:
1. Adenosine triphosphate (ATP)
- Phototrophs – convert light energy to ATP through photosynthesis
- Heterotrophs – convert chemical energy to ATP
- ATP is stored in energy-rich phosphoric anhydride bonds of the ATP molecule
- ATP is the energy currency of the cell
2. NAD+ /NADH
- Substrates of catabolism are in a reduced state
- Catabolism is oxidative so it reducing equivalents are released
- Transfer to NAD+ to from NADH
- NADH is used in mitochondria to produce ATP
3. NADP+/ NADPH
- Phototrophs use light energy to transfer electrons from H2O
- Heterotrophs hydrogenases transfers electrons from substrates
, - Source of reducing equivalents in the cell
Catabolism is reduced fuel and transferred into oxidized product (go from NADP+ to NADPH)
Anabolism is oxidized precursor and is transferred into reductive biosynthetic product
(NADPH to NADP+)
Metabolism is highly regulated:
Regulation is for efficiency – molecules degraded to fulfil the cell’s needs for energy and
reducing power, this is achieved by regulating enzymes. Cells only produce enough ATP for a
mechanism to occur, this limits wastage.
Enzyme regulation:
1. Allosteric
2. Covalent modification
3. Expression
Metabolism is compartmentalized:
Prokaryotes (no organelles):
- Some processes are localized to the plasma membrane e.g. oxidative
phosphorylation
- Multi-enzyme complexes – intermediates transferred between enzymes (limit
diffusion), would enzyme-substrate complex is actually the substrate complex
needed for the next enzyme-substrate complex to form
Eukaryotes:
- Some processes are localized to organelles, e.g. TCA cycle and oxidative
phosphorylation in mitochondria
- Is active transport is required, could serve as a mechanism of regulation.
Thermodynamics of biological systems:
Thermodynamics recap – relationship between heat, work and energy
It is the transfer of energy from one place to another (between system and surroundings) or
one form to another (chemical to heat)
These laws govern the behaviour of systems, including biological systems (why one reaction
is spontaneous and another is not).
Isolated systems – no exchange of energy or matter (between system and surroundings)
Closed systems – exchange of energy and not matter (between system and surroundings)
Open systems – exchange of energy and matter (most biological systems)
1st law of thermodynamics – total energy of an isolated system is conserved, energy cannot
be created or destroyed therefore it is transformed from one form to another. Total amount
of energy in universe is conserved.
Internal energy of a system (E) is the sum of the energy of the molecules in the system
(Joules)
A change in internal energy of a system (DE) can only occur if the energy enters or leaves
system in the form of heat or work (closed system)
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