BIOL 2004 Lecture Notes - Lecture 3: Electron Acceptor, Citric Acid Cycle, Lithotroph
3 May 2018
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Department
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Chemotrophy
March 3, 2016
• Inorganic vs organic
• Catabolism – breaking down of organic molecules to make energy
• Anabolism – uses energy to create a product from organic molecules
Sources of Energy and Organic Carbon:
• Dominant carbon sources for biomass:
o Fix inorganic carbon = autotroph
o Use existing organic molecules = heterotroph
• Energy
o From light: photo-
o From chemicals: chemo-
Basic nutritional types of organisms
• Photoautotrophs = inorganic carbon organic molecules
• Chemoautotrophs = generate organic molecules from a chemical reaction (not sun)
• Photoheterotrophs = capture energy from sunlight but do not produce organic molecules
• Chemohetrotrophs = energy comes from existing organic molecules they acquired from
their environment
Two Types of Chemotrophs:
• Most chemoheterotrophs are Organotrophs
o Catabolism of organic molecules
o Often just called heterotrophy but organotrophy is more specific
• Chemoautotropha are Lithotrophs
o Energy from oxidising inorganic molecules
o E.g. sulfur, sulfide, ammonia, nitrate, Fe …etc
An organism’s relationship to oxygen:
• Aerobes – use oxygen as an electron acceptor
o Obligate – need oxygen for growth
o Facultative – use but do not require oxygen for growth
• Microanerophiles – prefer low levels of oxygen
• Anaerobes (no use for oxygen)
o Aerotolerant
o Obligate anaerobes
Humans are “aerobic chemo-organo-heterotrophs”
• Oxygen dependent
• Energy from chemicals (organic)
• Require existing organic carbon to make most of your new organic molecules
find more resources at oneclass.com
find more resources at oneclass.com
Core catabolism of organotrophs:
• Simple sugars are mostly from the breakdown of polysaccharides (like starch, cellulose,
pectin..etc)
• **Prokaryotes and fungi use exoenzymes to break down molecules to simple sugars and
take them into their cell
o lignin
o proteins
o lipids
Revision: Energy realisation in classic aerobic organotrophy (humans and some prokaryotes)
• GLYCOLYSIS (EMP pathway): Glucose (CH12O6) Pyruvate (3C)
o 2 ADP + 2 Pi 2 ATP
• TCA Cycle (in mitochondria)
o Every carbon undergoes oxidation
o 2 ATP + 6 CO2
During this process, electrons have been stripped off and care carried by NADH
• Respiration: Oxidative Phosphorylation
o Electron transport linked to ATP synthesis by proton motive force
o Within mitochondrial membrane
• bring electrons to ETC and oxygen is the external terminal electron acceptor
• H2O + ~ 30 ATP
Note:
• huge variety of energy-generating pathways in prokaryotes
• Enter-Doudoroff pathway: often used instead of classical glycolysis
Metabolic Diversity
• Much of the metabolic diversity in prokaryotes is seen when oxygen and/or organic
carbon is limited
• We will consider:
o Fermentations
o Anaerobic respiration
o Lithotrophy
Fermentations
• ~organotrophy without external electron acceptor
o no use of the ETC
o as a result, substrates and products must be in redox balance
• typically under anoxic (anaerobic) conditions
• low energy yields per unit of substrate
o large amounts of substrates converted
o large amounts of end-products created
• Example: Homolactic Fermentation (in some lactic acid bacteria)
o Glucose 2 pyruvate via glycolysis ; 2 NAD+ 2 NADH (w 24 e-)
o Reduction of 2 pyruvate 2 lactate; 2 NADH 2 NAD+
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Inorganic vs organic: catabolism breaking down of organic molecules to make energy, anabolism uses energy to create a product from organic molecules. Sources of energy and organic carbon: dominant carbon sources for biomass, fix inorganic carbon = autotroph, use existing organic molecules = heterotroph, energy, from light: photo, from chemicals: chemo- Two types of chemotrophs: most chemoheterotrophs are organotrophs, catabolism of organic molecules, often just called heterotrophy but organotrophy is more specific, chemoautotropha are lithotrophs, energy from oxidising inorganic molecules, e. g. sulfur, sulfide, ammonia, nitrate, fe etc. Humans are aerobic chemo-organo-heterotrophs : oxygen dependent, energy from chemicals (organic, require existing organic carbon to make most of your new organic molecules. Core catabolism of organotrophs: simple sugars are mostly from the breakdown of polysaccharides (like starch, cellulose, pectinetc, **prokaryotes and fungi use exoenzymes to break down molecules to simple sugars and take them into their cell lignin, proteins lipids.
