Catabolism and Electron Flow and Phototrophy

Gibbs free energy

energy available from any given rxn
- (-) delta G favors products

Enthalpy

heat energy of rxn
- generally exothermic to drive rxn

Entropy

disorder of rxn
- large S can drive rxns even if H is positive

ATP

energy carrier; high energy phosphate bonds in which hydrolysis releases energy

NAD+ and FAD

store e- on aromatic rings and movement of which releases energy

Activation energy

energy required for a reaction
- decreased by enzymes

Catabolism

break down of larger molecules to obtain energy

Sources of catabolism

- carbs, lipids, peptides, aromatics

Fermentation

put e- on some organic compound
- lower energy yield but less enzymes

Respiration

use e- transport system to put e- back on an inorganic final acceptor

Glycolysis

break down glucose to 2 pyruvate, 2 ATP, 2 NADH

ED Pathway

breakdown of sugar acids to pyruvate, 1 ATP, 1 NADH, and 1 NADPH
* can start with glucose

Pentose Phosphate pathway

start like other 2 but yields 2 NADPH and sugar intermediates for biosynthesis

Two steps to glycolysis

1. investment in energy
2. gain of energy

Lactic acid fermentation

put e- back on pyruvate to form lactic acid

Ethanolic fermentation

put e- back on pyruvate and release CO2

Tricarboxylic Acid Cycle (TCA)

further breakdown of pyruvate to generate lots of e- carriers
- started by acetyl CoA
- LOTS of enzymes

TCA overall yield

3 NADH, 1 FADH2, 1 ATP (for 1/2 glucose)
- oxaloacetate regenerated at end

Breakdown of aromatic molecules

makes catechol

Syntrophy

w/o oxygen, put aromatic e- on protons to make H2 so partner organism used H2 to allow original organisms catabolism to function
- negative H drives both metabolisms
- one organism does not grow w/o the other

ETS

membrane soluble e- carrier move e- and obtain energy in small amounts

Cytochromes

basis of ETS, part of larger oxidoreductase complexes (ORCs)

Proton motive force

movement of H+ for energy generation

metabolism

classified by initial e- donor

Organotrophs

organic initial donor
- aerobic or anaerobic

Lithotrophs

inorganics initial donor
- aerobic or anaerobic

Phototrophs

light capture to split H20 or H2S

Quinones

energy transfer in double bonds/aromatic rings

NADH dehydrogenase (NDH1)

first ORC, takes e- from NADh, bounces them down to a quinone and pumps 4 protons

Oxidative phosphorylation

using ETS energy to make ATP through PMF

ATP synthase

proton enters C unit, rotates gamme core, rot. energy in alpha and beta subunits makes ATP

Bacteriorhodopsin

light causes a conformational change in retinal to pump a proton (in archaea)
- called proteorhodopsin in bacteria

Photolysis

light energy absorbed to split e- from a donor (usually H2O or H2S)

Chlorophylls

absorb light E in their chromophores

Antenna complexes

arrangement of chlorophylls in a way to best catch as many photons

PS1

e- is replaced by cleavage of H2S, H2, or from metal ions (NOT H2O)
- makes NADPH
- no pumping of protons

PS11

e- replaced by ETS
- pumps protons, makes NADH
- purple bacteria, proteobacteria

Oxygenic photolysis

only by cyanobacteria and eukaryotes
- chromophores absorb higher energy light so can split H2O to make O2
- pumps protons and makes NADPH
- used BOTH photosystems