Typed lecture notes covering chapter 13 of Microbiology: An Evolving Science, the textbook used in the "General Microbiology" course (BioM122) at UCI. Aligns with lecture 7.
Microbial Metabolism I (Ch. 13, Lec. 7)
Monday, October 19, 2020 11:00 AM
Active learning (10/19):
• 13.1: Energy of Life • Soap and/or ethanol uses physical and chemical properties to kill bacteria.
• Catabolism: Breakdown of complex molecules into smaller ones. Better than antibiotic-filled soap.
○ provides energy for anabolism, but some energy is released as heat. • What type of metabolism generates more ATP? Anaerobic or aerobic
○ Polymers -> monomers -> molecules respiration of glucose?
• Anabolism: rxns that build molecules.
• Cells use energy to assemble simple, disordered molecules into complex, ordered forms.
○ However, the total metabolism of all life forms dissipates as heat.
○ Sunlight powers photosynthesis and adds to the biomass of the earth; however, most of that energy dissipates
into heat outside of the earth.
• Microbes(bacteria and archaea) use more diverse energy sources than multicellular organisms:
○ Chemotrophy: yields energy from electron transfer b/w chemicals.
• Chemo-organo-trophy: use electrons from organic compounds.
• Chemo-litho-trophy: use electrons from inorganic compounds.
○ Phototropy: yields energy from light absorption.
• Photo-auto-trophy: light absorption w/ CO2 fixation.
• Photo-hetero-trophy: light absorption w/o CO2 fixation.
•
Gibbs free energy change, deltaG: deltaG = deltaH - T*deltaS
○ deltaH: change in enthalpy, the heat absorbed/released.
○ TdeltaS: product of temp and entropy change.
○ deltaG < 0, process will go forward.
○ deltaG > 0, process will go in reverse.
○ Calculating the deltaG value of a rxn can predict how much biomass microbes will build (favors negative G).
• 13.2: Energy carriers and electron transfer
• Energy carriers: molecules that gain or release small amts of energy in reversible rxns. Ex. NADH, ATP. Some
energy carriers also transfer electrons:
○ Electron donor: a reducing agent.
○ Electron acceptor: an oxidizing agent.
• Redox rxns: oxidation rxn (removal of an electron) is paired w/ a reduction rxn (gaining of electron).
• Adenosine triphosphate (ATP): contains a base (adenine), a sugar (ribose), and 3 phosphates.
○ Under physiological conditions , ATP always forms a complex w/ Mg2+. (Why magnesium is an essential
nutrient)
○ ADP + P = ATP!
○ Medium-sized energy carrier b/c the cell contains many phosphorylated molecules that undergo hydrolysis to
yield greater energy. Other nucleotides can also carry energy!
• ATP can transfer energy to cell processes in 3 different ways:
1. Hydrolysis-releasing phosphate (Pi),
2. Hydrolysis-releasing pyrophosphate (PPi), or
3. Phosphorylation of an organic molecule.
• NADH: nucleotide that carries 2-3 times as much energy as ATP. Donates and accepts electrons:
○ NADH: the reduced form
○ NAD+: the oxidized form.
• Overall reduction of NAD+ consumes 2H to make NADH:
• NAD+ + 2 H+ + 2 e– → NADH + H+ ΔG°′ = 62 kJ/mol
• FAD: coenzyme that can also transfer electrons.
○ FADH2: the reduced form.
• Weaker electron donor than NADH. Electrons are transferred and energy is released when FADH2 is
combined w/ a strong electron acceptor.
○ FAD: the oxidized form.
• Reduced by 2 electrons and 2 protons(H+).
• Moving a substance against its conc gradient requires energy. Alt, a conc gradient across the membrane can be
sued to store energy for the cell.
• Enzyme catalyze biological/chemical rxns.
○ Lowering the activation energy (Ea) makes for a faster rxn.
• 13.3: Catabolism: the Microbial Buffet
• Polysaccharides -> Disaccharides -> Monosaccharides. Sugars are catabolize by pyruvate. Pyruvate is further
catabolized to CO2 or H2O via TCA cycle, or fermented.
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