Post on 08-Feb-2016
description
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