Microbio Ch.11

What are the sources of energy?

Energy, electrons, and carbon

Energy

Phototrophs (light) vs. chemotrophs (chemical oxidation)

Electrons

Lithotrophs (inorganic compounds) vs. Organotrophs (organic compounds).

Carbon

Autotrophs (CO2​ as primary source) vs. Heterotrophs (reduced organic molecules)

Photolithoautotroph

Light energy, inorganic e− donor, CO2​ carbon source

Photoorganoheterotroph

Light energy, organic e− donor, organic carbon source

Chemolithoautotroph

Inorganic chemical energy/e− donor, CO2​ carbon source

Chemolithoheterotroph

Inorganic chemical energy/e− donor, organic carbon source

Chemoorganoheterotroph

Organic chemical energy/e− donor/carbon source

What are the three major chemoorganotrophic fueling processes?

Aerobic respiration, anaerobic respiration, and fermentation

Aerobic respiration

Uses an electron transport chain (ETC) with O2​ as the final electron acceptor

Anaerobic respiration

Uses an ETC with an inorganic terminal electron acceptor other than O2​ (e.g., NO3−​, SO42−​, CO2​)

Fermentation

Does NOT use an ETC; an endogenous organic molecule (e.g., pyruvate) serves as the final electron acceptor to re-oxidize NADH back to NAD+

What is the function of the Embden-Meyerhof glycolytic pathway?

Oxidizes 1 glucose (6C) into 2 pyruvate (3C), yielding net 2 ATP and 2 NADH

What is the cellular location of the Embden-Meyerhof glycolytic pathway?

Occurs in the cytoplasm of both prokaryotes and eukaryotes

High-energy intermediates

Intermediates with higher phosphate transfer potential than ATP include 1,3-bisphosphoglycerate (1,3-BPG) and phosphoenolpyruvate (PEP)

Substrate-Level Phosphorylation

Synthesis of ATP by direct transfer of a high-energy phosphate group from a phosphorylated intermediate to ADP (e.g., PEP converting to pyruvate via pyruvate kinase)

Where does the TCA cycle occur?

Cytoplasm in prokaryotes (bacteria/archaea); mitochondrial matrix in eukaryotes

What are the yields of the TCA cycle?

Generates 4 CO2​, 6 NADH, 2 FADH2​, and 2 GTP/ATP (via substrate-level phosphorylation)

TCA cycle events

Acetyl-CoA combines with oxaloacetate (4C) to form citrate (6C); fully oxidizes acetyl carbon to CO2​

Pyruvate Dehydrogenase Complex

Multi-enzyme complex that converts pyruvate (3C) into acetyl-CoA (2C), releasing 1 CO2​ and 1 NADH per pyruvate

ATP Synthase

Membrane-bound enzyme complex that allows protons to flow back down their concentration gradient, using this rotary energy to phosphorylate ADP to ATP

Proton Motive Force (PMF)

An electrochemical gradient across the membrane (composed of a chemical pH gradient and an electrical charge potential) used to drive cellular work, including ATP synthesis, motility, and active transport

Chemiosmotic Hypothesis

As electrons flow down the ETC from carriers with lower E0′​ to higher E0′​, protons (H+) are pumped across the membrane, establishing a proton motive force

Location of eukaryotic ETCs

Inner mitochondrial membrane

Location of bacterial/archaeal ETCs

Plasma membrane

Bacterial adaptability of bacterial ETCs

Bacterial ETCs are often branched, shorter, and can adjust their electron carriers based on oxygen availability (e.g., E. coliuses the high-affinity bd branch in low O2​ and the bo branch in high O2​). They yield less ATP per electron pair than eukaryotic ETCs

Yield of substrate-level phosphorylation

Yields 4 net ATP total (2 from glycolysis + 2 from TCA cycle)

Yield of oxidative phosphorylation

Produces the majority (up to ~28–30 ATP in ideal aerobic eukaryotic conditions, totaling ~30–32 ATP per glucose)

Yield of anaerobic respiration

Yields less ATP than aerobic respiration because non-O2​ terminal acceptors (like NO3−​ or SO42−​) have less positive reduction potentials (E0′​) than O2​, resulting in a smaller ΔE0′​ and less energy available to pump protons

Conditions of fermentation

Occurs in the absence of oxygen or when an ETC is absent or non-functional

Main purpose of fermentation

Re-oxidize NADH back to NAD+ so that glycolysis can continue producing ATP via substrate-level phosphorylation

Key features of fermentation

No ETC used; no oxidative phosphorylation; terminal electron acceptor is an endogenous organic compound (e.g., pyruvate or pyruvate derivative)

Lactic Acid fermentation

Reduces pyruvate directly to lactate