3. Microbial Metabolism Flashcards
catabolism
fueling reactions
energy-conserving reactions
provide ready source or reducing power (electrons)
generate precursors for biosynthesis
anabolism
the synthesis of complex organic molecules from simpler ones
requires energy from fueling reactions
nutrients
supply of monomers (or precursors of) required by cells for growth
macronutrients
nutrients required in large amounts
micronutrients
nutrients required in minute amounts
trace metals and growth factors
requirements for nutrition in cells
carbon
hydrogen
oxygen
phosphorous
sulfur
nitrogen
carbon
major element in all classes of macromolecules
most microbes (heterotrophs) use
organic carbon
autotrophs use
carbon dioxide
nitrogen
proteins, nucleic acids, and many more cell consituents
phosphorous
nucleic acids and phospholipids
sulfur
sulfur containing amino acids (cysteine and methionine)
vitamins (thiamine, biotin, lipoic acid)
potassium
required by enzymes for activity
iron (Fe)
cellular respiration
trace metals
enzyme cofactors
active transport
how cells accumulate solutes against concentration gradient
three classes of transporters:
simple transport
group translocation
ABC system
simple transport
driven by the energy in the proton motive force
group translocation
chemical modification of the transported substance driven by phosphoenolpyruvate
ABC transporter
periplasmic binding proteins are involved and energy comes from ATP
phosphotransferase system in E.coli
-best studied group translocation system
-glucose, fructose, mannose
-five proteins required
-energy derived from phosphoenolpyruvate (from glycolysis)
ABC (ATP-binding cassette) systems
200+ different systems identified in prokaryotes for organic and inorganic compounds
high substrate affinity (very specific to what they are transporting)
ATP drives uptake
requires trans-membrane and ATP-hydrolyzing proteins plus:
-gram negatives employ periplasmic binding proteins
-gram positive and archaea employ substrate-binding proteins on external surface of cytoplasmic membrane
activation energy
minimum energy required for molecules to become reactive
-a catalyst is usually required to overcome activation energy barrier
electron donor
the substance is oxidized (glucose)
electron acceptor
the substance is reduced (O2)
organic molecules contain
1 C or more and H
classification of organisms based on their metabolism:
- energy source
- electron donor
- carbon source
energy source
sunlight: photo- (light E)
preformed molecules: chemo- (chemical E)
electron donor
organic compound (organo-)
inorganic compound (litho-)
carbon source
organic compound (hetero-)
carbon dioxide (auto-)
thiobacillus denitrificans oxidizes ammonia (NH3) for energy to conserve ATP and fixes CO2
chemolithoautotroph
a group of marine organisms, the “thiosulfate (S2O3)- oxidizing bacteria” obtain energy via the oxidation of thiosulfate. Many of these organisms require pyruvate for growth
chemo litho heterotroph
organisms in the genus roseobacter can obtain energy via aerobic anoxygenic photosynthesis and they require glucose for growth
photo organo heterotroph
Reduction Potential (E0)
tendency to donate electrons (expressed as volts)
Electron Tower
top –> bottom
donor on “right”
acceptor on “left”
donor is always above acceptor
the further apart, the more potential (ATP)
a couple on the same level cannot generate any potential
the greater the difference between the reduction potential of the donor and the reduction potential of the acceptor,
the more negative the free energy change
chemical energy released in redox reactions is primarily stored …
chemical energy is also stored in …
in certain phosphorylated compounds
-ATP: the prime energy currency
-phosphoenolpyruvate
coenzyme A derivates
adenosine triphosphate
energy stored in phosphate bonds
long-term energy storage involves biosynthesis of
insoluble polymers that can be oxidized to generate ATP
prokaryotes:
-gylcogen
-elemental sulfur
eukaryotes
-starch and lipids
two reaction series are linked to energy conservation in chemoorganotrophs:
fermentation and respiration
they differ in the mechanism of ATP synthesis
fermentation
substrate level phosphorylation;
ATP is directly synthesized from an energy-rich intermediate
krebs cycle, glycolysis
respiration
oxidative phosphorylation;
ATP is produced from proton motive force formed by transport of electrons
ETC
Fermentation
all about regenerating NAD+
-no electron acceptor
-no ATP
-purely anaerobic (no oxygen product)
byproduct: alcohol, CO2, acid
2 ATP formed by substrate level phosphorylation in glycolysis only
no Krebs cycle or ETC, so NADH reduces an endogenous electron acceptor
some endproducts:
alcohol fermentation - CO2, alcohol
homolactic fermentation: lactic acids
heterolactic fermentation: lactic acids, CO2, alcohol
aerobic respiration:
O2 as acceptor
(glucose is an electron donor)
anaerobic respiration
all but O2 is an acceptor
(glucose is an electron donor)
which would make more ATP? fermenting or respiring
respiring
which would consume more glucose to make the same amount of ATP?
fermenting
what if you add nitrate to the no O2 fermenting
if you add NO2, that is an electron acceptor, so you would go from fermenting to anaerobic respiration
photosynthesis : the reverse of respiration
photo: converting light energy (photons) to chemical energy ATP
synthesis: fixing CO2 into organic molecules- a reductive process
-to fix CO2, a lot of energy and a lot of reducing power is needed
oxygenic photosynthesis
source of energy is light
source of reducing power: oxidation of water
H20 –> O2
anoxygenic photosynthesis
source of energy is light
reducing power is oxidation of inorganic or organic chemicals
H2S –> S
(no oxygen)
oxygenic photosynthesis requires
two photosystems: chlorophyll is the main pigment
the only organism in the microbial word that does oxygenic photosynthesis is
cyanobacteria
in light dependent reactions,
water and sunlight produce the ATP
in light dependent reactions
NADPH is needed to fix CO2 into sugar
anoxygenic photosynthesis requires
only one photosystem
H20 is NOT used, no O2 produced
use alternative pigments and generate NADPH differently:
-direct oxidation of H2
-reverse electron flow
anoxygenic phototrophs
energy from light but reducing power from organic or inorganic sources
habitat: anoxic environments that are exposed to light
purple sulfur
electron donor: H2S
special features: anaerobic anoxygenic
bacteriochlorophylls: a and b (photosystem II)
purple nonsulfur
electron donor: organic substrates
special features: anaerobic anoxygenic also chemotrophic
bacteriochlorophylls: a and b (photosystem II)
green sulfur
electron donor: H2S
special features: anaerobic anoxygenic
bacteriochlorophylls: c, d, e (photosystem II)
green nonsulfur
electron donor: organic substrates
special features: facultative aerobic; can also perform chemotrophy
bacteriochlorophylls: c (photosystem II)
