Lecture 9 Bioenergetics

Redox reaction

A reaction where electrons are transferred from an electron donor to an electron acceptor - the basis of how organisms get energy

Oxidation vs reduction

Oxidation is loss of electrons and reduction is gain of electrons (OIL RIG)

Electron transport chain (ETC)

A sequence of electron carriers that perform coupled redox reactions to pump H+ across a membrane

Electrochemical gradient

A difference in charge and concentration of ions (usually H+) across a membrane used to do work

Chemiosmosis

Making ATP by letting H+ flow down its gradient through ATP synthase

ATP synthase

Membrane enzyme that converts the H+ gradient into ATP

Substrate-level phosphorylation

Making ATP by directly transferring a phosphate from an organic substrate to ADP (as in glycolysis)

Oxidative phosphorylation

ATP made by an ETC plus chemiosmosis with O2 as the final electron acceptor

Glycolysis

Breakdown of glucose into 2 pyruvate yielding 2 ATP and 2 NADH

Fermentation

Process after glycolysis when O2 is absent that makes ATP only by substrate-level phosphorylation (alcohol or lactic acid)

Aerobic respiration

Glycolysis plus citric acid cycle plus ETC with O2 as final acceptor yielding about 30 to 32 ATP per glucose

Anaerobic respiration

Respiration using an ETC with a final electron acceptor other than O2 such as SO4 2- or CO2 or Fe3+

Why O2 is the best final electron acceptor

O2 releases the most energy when it accepts electrons so aerobic respiration yields the most ATP

Why energy is released in small steps

An ETC releases energy gradually across many carriers so cells can capture it instead of losing it all at once

Autotroph vs heterotroph

Autotrophs get carbon from CO2 and heterotrophs get carbon from organic compounds

Phototroph vs chemolithotroph vs chemoorganotroph

Energy from light vs inorganic chemicals vs organic chemicals

Photoautotroph

Light for energy and CO2 for carbon - cyanobacteria and algae and plants

Photoheterotroph

Light for energy and organic compounds for carbon - halophilic archaea

Chemoorganoheterotroph

Organic compounds for both energy and carbon - most prokaryotes and all animals and fungi

Chemolithoautotroph

Inorganic compounds for energy and CO2 for carbon - methanogens and sulfur-oxidizing and nitrifying bacteria

Methanogens

Strict anaerobic archaea that use H2 as donor and reduce CO2 to CH4

Anoxygenic vs oxygenic photosynthesis

Anoxygenic uses donors like H2S and releases no O2 (purple sulfur bacteria) while oxygenic splits water and releases O2 (cyanobacteria and plants)

Bacteriorhodopsin

Light-driven proton pump in halophilic archaea that makes an H+ gradient without an ETC

Mitochondria and chloroplasts

Descendants of endosymbiotic alpha-proteobacteria and cyanobacteria that both use ETCs to make ATP

What all ETCs have in common

Homologous carriers from a shared evolutionary origin and the same end product - an H+ gradient for ATP synthesi