Metabolism

Harvesting energy from molecules (catabolism)

Using energy to synthesize molecules and theirsubunits: synthesis of sugars, amino acids,etc.

How do organisms harvest energy?

Cells use metabolic pathways to control anduse energy released in catabolism

Through stepwise metabolic pathways

p. 132

Enzymeslower activation energy (are catalysts)

are specific

are proteins (i.e., sensitive to environmental conditions)

p. 133

What about those electrons?

In these reactions, electrons are donated by(removed from) the energy sourceand transferred to another compound

The energy source is oxidized

The recipient molecule is reduced

Some molecules function in the cell as electron carriers (they are reduced andthen oxidized)

Major electron carriers

NAD+, FAD: participate ultimately in ATPsynthesis

A terminal electron acceptor is requiredIn aerobes it is oxygen

In anaerobes it is something else

NADP+ is used in biosynthetic pathways

Precursor metabolites

Are used in catabolic pathways

Can be used in anabolic pathways, too

Many microbes can make all cell components(including all amino acids) from precursors

(they can grow in minimal medium)

p. 135

p. 136

Glycolysis, Krebs, ETC/OP look familiar

Some bacteria use variations on glycolysis(still get pyruvate, but different intermediatesare formed)Pentose phosphate pathway can also be usedfor energy, but is more commonly used to make

5-carbon sugars (where do you find these?)

RespirationLots of reducing power (NADH, FADH2)

Terminal electron acceptor required to regen-erate electron carrier (oxygen, nitrate,carbon dioxide or other inorganic molecule)

If not available, cells cannot respire

Some can ferment insteadpyruvate or derivative is used as terminalelectron acceptor

Why can organism not respire?

No terminal electron acceptor is available

Some are “obligate fermenters” (can’t useoxygen although they are not killed by it)example: lactic acid bacteria

They get their ATP from glycolysis

Different organisms have different fermentationpathways

These differences can be commerciallyuseful, or can be useful in identification

Glycolysis (or variant, producing pyruvate)and Krebs (TCA) cycle are commonto respiring cells

Prokaryotes: whole process occurs in cytoplasm

Eukaryotes: oxidative decarboxylation of pyruvateis required in process of getting into themitochondrion (where Krebs cycle occurs)

glycolysis

Krebs cycle

Aerobic respiration

Electron transport chain (energy from electronsis released; proton gradient is generated

Oxidative phosphorylation: proton motive forceis used to synthesize ATP

In inner mitochondrial membrane

In plasma membrane of E. coli

Anaerobic respiration is less efficientless energy released in reductionof compounds other than oxygen

Different electron carriers

Several pathways exist for reducing nitrate

What do organisms use for energy?

Organotrophs can use many organic moleculesbesides glucose, if they have the rightenzymes

Polysaccharides- amylase, cellulaseDisaccharides must be converted to mono-

saccharidesMonosaccharides (like mannose or galactose)

must be modified

Lipases, proteases

Chemolithotrophs can use inorganic substancesfor energy; many of these are products ofanaerobic respiration

p. 155

Photosynthesis

Photosynthetic organisms convert light energyto chemical energy

They are the ultimate energy source foreverything else

Pigments are used to capture light (radiant)energy

Generate ATP; also reducing power to fixCO2 and form sugar (C6H12O6)

p. 157

Prokaryotes tend to be similar in anabolicprocesses

Use ATPUse NADPH for reducing powerHave enzymes to make precursors and put them

together to form macromolecules

Fastidious organism don’t have the enzymes, somacromolecules must be provided

LipidsAmino acidsNucleic acids