CH 14 flashcards

Introduction to Metabolic Diversity

  • Energy Source Classifications:

    • Phototroph: Energy from light.

    • Chemotroph: Energy from chemical compounds.

      Reducing Power Source:

    • Lithotroph: Uses inorganic sources.

    • Organotroph: Requires organic compounds.

    • Autotroph: Uses inorganic carbon. self-fed

    • Heterotroph: Uses organic carbon. needs help from others

  • All Eukaryotes:

    • unique trait: chloroplasts

      • photolithoautotrophs, e.g plants and algae

      • light + inorganic e- source + CO₂

      • Chemoorganoheterotrophs, e.g. animals and fungi.

      • chemical + organic e- source + organic carbon

        • restricted to these 2 because derived from cyanobacteria and chloroplasts, which are believed to have originated from endosymbiotic relationships with these organisms.

  • All Prokaryotes:

    • photolitho-hetero/autotroph

    • chemolitho-hetero/autotroph

    • mixotroph (hetero+auto)

    • chemoorganoheterotroph

  • Phototrophy and respiration (must involve membrane):

    • involve ETC (transfer of e- to produce energy) and PMF (creates ATP), which are essential for ATP synthesis in both phototrophic and heterotrophic organisms. In phototrophs, light energy is captured and converted into chemical energy, while in chemoorganoheterotrophs, organic molecules are oxidized to release energy.

Autotrophic Pathways

can assimilate (take in) CO2 into cellular materials e.g. photo/chemolithotrophs

  • Calvin Cycle:

    • Primary CO2 fixation method (CO2 → organic compounds)

    • common in cyanobacteria, algae, and plants (oxygenic phototrophs), purple bacteria, aerobic chemolithotrophic bacteria.

    • Key enzyme: RubisCO (located in carboxysomes).

      • reduces CO2 → G3P

    • Requires 12 NADPH (reducing power) and 18 ATP to create 1 fructose-6-phosphate from CO2.

  • Reverse Citric Acid Cycle (rTCA): AKA reductive TCA

    • Used by green sulfur bacteria (Chlorobium) and anaerobic or mircoaerophilic chemolithotrophic bacteria.

    • Functions in CO2 reduction; efficient with lower energy requirement compared to Calvin Cycle.

    • 24H and 10 ATP to fix 6 CO2 into organic compounds to get 1 glucose molecule

    • requires enzymes not found in citric acid cycle

      • alpha-ketoglutarate, pyruvate synthase, etc.

  • reverse/opposite from “Can I Keep Selling Sex For Money Officer”

    • citrate → Acetyl-CoA → pyruvate → phosphoenolpyruvate → G3P

Comparison of Electron Flow

Water in cyclic photophosphorylation provides electrons and protons

  • Purple Bacteria:

    • cyclic electron flow

    • an-oxygenic photosynthesis, produce energy without O2 as byproduct

    • use hydrogen sulfide for reducing power

  • Green Sulfur Bacteria

    • anoxygenic

    • rely on hydrogen sulfide as electron donor

    • contains chlorosomes, house bacteriochlorophylls.

  • Cyanobacteria:

    • water as electron donor

    • not cyclic

    • oxygenic bc O2 is produced

    • 2 photosystems

  • Oxygenic vs Anoxygenic Phototrophs:

    • photophosphorylation. sunlight → PMF → ATP production

    • takes place in the thylakoid membranes of chloroplasts or in the cell membrane (in photosynthetic prokaryotes).

    • Oxygenic phototrophs release oxygen, while anoxygenic ones do not.

  • Oxygenic:

    • H2O electron donor → split and release O2 during photosynthesis.

    • produce ATP

    • cyanobacteria

  • Anoxygenic:

    • H2S electron donor → sulfur as byproduct made.

    • produce ATP

    • if the membrane is damaged (thylakoid) → disrupts ETC = ATP production will decrease or stop

    • phototrophic purple & green bacteria

  • Oxygenic Photosynthesis:

    • Eukaryotes (plants and algae): occur in chloroplast

    • Cyanobacteria: occur in stacked membrane (thylakoids) in cytoplasm

      • stacked thylakoids = increase space/size in membrane

      • inner membrane: for energy

      • thylakoid space = lowest pH

  • Electron Transport in Oxygenic Photosynthesis: 2 photosystems

    • Cyanobacteria acquire PS1 and PS2 through HGT which allows them to harness energy for photosynthesis

    • PSI and PSII → noncyclic

    • noncyclic electrons: reduce NADP+ → NADPH

    • From PS1, electrons pass through ETC then they return to PS1

    • PSII

      • split water , make ATP

      • byproduct: O2

      • electron source: water (water oxidizing complex)

    • PSI

      • reduce NADP+ → NADPH

      • byproduct: NADPH

      • electron source: e- from PSII

    • Photophosphorylation: Sunlight → PMF → ATP production

Photophosphorylation vs. Oxidative Phosphorylation

  • Photophosphorylation:

    • occurs in the thylakoid membranes of chloroplasts

    • utilize light energy to generate a proton motive force (PMF)

  • oxidative phosphorylation:

    • occurs in the inner mitochondrial membrane

    • use energy released from ETC (NADPH/FADH2) to create ATP.

  • BOTH:

    • PMF

    • ATP synthase

    • ETC

    • membrane

Sulfur Bacteria

  • Sulfate and Sulfur Reduction:

    • Sulfate reduction:

      • sulfate (SO4²-) → sulfide (H2S) by sulfate-reducing bacteria

    • Sulfur Reduction;

      • sulfur (S) → sulfide (H2S) through the metabolic processes of sulfur-reducing bacteria

    • Sulfide → sulfate = decrease pH

Iron Oxidation

  • Chemolithotrophic Bacteria:

    • Oxidize ferrous iron (Fe2+) (high H+ concentration)→ ferric iron (Fe3+) which is easily oxidized in the presence of air

    • ferric hydroxide (Fe(OH)3) precipitates water, decreasing environmental pH.

    • Many Fe oxidizers strongly acidophilic → rusting, corrosion

Nitrification Process

  • Chemolithotrophic Nitrifying Bacteria:

    • Convert ammonia (NH3) → nitrite (NO2−) → nitrate (NO3−) through specific aerobic oxidation processes.

    • Important contributors in soil, water, and wastewater systems.

    • Nitrifiers can only catalyze one set of reactions

      • ammonia (NH3) → nitrite (NO2-) by nitrosomonas and nitrosopumilus

      • nitrite (NO2-) → nitrate (NO3-) by nitrobacter

    • anammox bacteria: covert NH2 → N = good for waste water treatment plan

  • Nitrate Reduction and Denitrification (use electron acceptors):

    • Nitrate reduction: anaerobic and aerobic

      • nitrate (NO3-) → nitrite (NO2-) or further to nitrogen gas (N2) and other nitrogenous compounds.

    • Denitrification: anaerobic

      • final step in the nitrogen cycle, where denitrifying bacteria convert nitrates back into nitrogen gas, releasing it into the atmosphere and completing the cycle.

Respiratory Processes

  • Assimilative:

    • process that consumes energy

    • reduced form of element becomes part of the biomass of the organism

    • autotrophic pathways

    • e.g. bacteria that take in sulfur from the environment to make cysteine is assimilative sulfate reduction

  • Dissimilative:

    • energy conserved, sulfate reduction is used to convert sulfate into hydrogen sulfide

    • Steps: in reduction of nitrate

      1. Nitrate → Nitrite → Nitric Oxide → Nitrous Oxide → nitrogen gas

      2. enzymes in order: Nitrate reductase → nitrite reductase → nitric oxide reductase → nitrous oxide reductase

        Gases: nitric oxide, nitrous oxide, and dinitrogen

Key Nitrogen Compounds and Oxidation States

  • Oxidation States:

    • Includes ammonia (−3), nitrate (+5), and nitric oxide (+2), indicating the versatility of nitrogen transformations in ecosystems.

Methanogenesis

  • Process:

    • Biological methane production catalyzed by methanogens (strictly anaerobic Archaea).

    • Important in ecological settings like wetlands and digestive systems.

    • methanogenesis is also a form of anaerobic respiration (CO2 reduction by H2)

    • uses coenzyme M to transfer electron and reduce carbon

Energetic and Redox Considerations

Fermentation Characteristics

  • Energy Conservation:

    • Lacks ETC or PMF; thus, lower energy yield compared to respiration.

    • Achieves balance through substrate-level phosphorylation.

    • lack electron acceptor

Discussion

  • Beer produced by yeast fermentation is done in closed or seal fermentor. What will happen if fermentor is open?

    • ethanolic fermentation dont occur robustly in O2 presence because respiration will take over → complete breakdown of glucose into CO2 and H2O

    • contamination, or further oxidation into products like aldehyde or acid