Chapter 14: Metabolic Diversity of Microorganisms Flashcards
Light reaction
produces ATP and NADPH
- requires an electron donor from environment (water, H2S, H2)
Dark reactions
reduce CO2 to cell material for growth
requires ATP and e- (NADH/NADPH)
oxygenic photosynthesis
oxidation of H2O produces O2
-cyanobacteria
anoxygenic photosynthesis
oxidation of H2S produces SO42-
-purple/green sulfur bacteria
chlorophyll and bacteriochlorophyll
tetrapyrroles w magnesium
- different pigments allows different phototrophs to absorb different wavelengths
photocomplexes
proteins housed within membranes
- reaction centers contain pigments
- antennae pigments surround and funnel light energy to rxn centers
chloroplasts
in eukaryotes
- intercellular organelles containing thylakoids
thylakoids
sheet-like membrane systems
chlorosomes
capture low light intensities
- in anoxygenic green sulfur bacteria, filamentous anoxygenic phototrophs, & phototrophic Acidobacteria
Carotenoids
widespread accessory pigment
hydrophobic
yellow, red, orange, brown, or green
absorb blue light
-quenches toxic oxygen species, prevents dangerous photooxidation
phycobiliproteins
the main light-harvesting systems of cyanobacteria and red algae chloroplasts
- red/blue-green tetrapyrroles: “bilins” bound to proteins
pro: integrated into cytoplasmic membrane
purple bacteria: chromatophores/lamellae
cyanobacteria: thylakoids
phycoerythrin
absorbs ~550nm (red)
phycocyanin
absorbs ~620 nm (blue)
noncyclic photophosphorylation
e- do not circle back and reduce NADP+ to NADPH
cyclic photophosphorylation
occur if cell requires less NADPH to produce more ATP
autotrophy
CO2 is reduced and assimilated into cells
- in phototrophs: often called “dark rxn”
Calvin Cycle
Requires:
6 CO2
CO2 acceptor
12 NADPH
18 ATP
RuBisCO
phosphoribulokinase
To make 1 Glucose
carboxysomes
inclusions containing and improving efficiency of RubisCO in many autotrophs
- increase CO2 concentration (instead of O2)
-250 RubisCO/carboxysome
Reverse Citric Acid Cycle
aka reductive TCA cycle
used by green sulfur bacteria (and some chemoautotrophs)
more efficient:
4 NADH
2 reduced ferredoxins
10 ATP
Hydroxypropionate Cycle
2 CO2
6 H
3 ATP
into glycoxylate
Nitrogen fixation
atmospheric gaseous N2 -> ammonia NH3
- no eukaryotes fix nitrogen
16 ATP
nitrogenase
enzyme complex composed of dinitrogenase and dinitrogenase reductase
-inhibited by oxygen
Ways of protecting nitrogenase from oxygen
oxygen-retarding slime layer
removal by respiration
anoxic heterocyst formation
Assaying nitrogenase
acetylene reduction
-nitrogenases reduce other triply bonded compounds, including acetylene, to form ethylene
assimilative reduction
consumes energy
ie. NO3-, SO4-, and CO2 reduction for new sources of N, S and C for new cell material
dissimilative reduction
conserves energy
product of reduction is a small molecule that is excreted (N2, H2S, CH4)
- only in anaerobic respiration
H2 oxidation
H2 + 1/2 O2 -> H2O
very exergonic, can be coupled to ATP synthesis
catalyzed by hydrogenase
H2 bacteria
most are chemoorganotrophs
CO2 fixed by Calvin Cycle
Oxidation of Sulfur compounds
H2S, S0, S2O3- (SO3 2- common)
in stages, first produces S0 (deposited in cell as an energy reserve)
produces H+ (acidifies environment)
Sox system
facultative chemolithotrophs
repress synthesis of Calvin cycle and hydrogenase enzymes when organics present catalyzed by hydrogenase
Sox System
oxidizes reduced sulfur compounds directly to sulfate
4 key proteins: SoxXA, SoxYZ, SoxB, SoxCD
sulfur-oxidizing microbes that store sulfur granules lack _______
SoxCD (sulfur dehydrogenase)
chemoautotrophs
aerobes oxidizing ferrous iron at low pH
Fe2+ -> Fe3+
ferrous hydroxide
Fe3+ + 3 H2O = Fe(OH)3 + 3 H+
insoluble, precipitates in water, driving down pH
Bioleaching
Assimilative sulfur metabolism
incorporation of sulfate for biosynthetic purposes to make cysteine, methionine, and other organosulfur compound
Dissimilative sulfur metabolism
use of sulfate as an electron acceptor for energy conservation and production of large amount of H2S (excreted)
Sulfur reduction
1 ATP/SO4- reduced to HS-
e- transport reactions lead to PMF formation
methanogenesis
biological production of methane
catalyzed by strictly anaerobic Archaea (methanogens)
- form of anaerobic respiration
reduction of CO2by H2 to form CH4
NEEDS TRUE ANOXIC CONDITIONS
methanogens
present in freshwater sediments, sewage sludge digesters, bioreactors, animal intestines
C1 carriers
coenzyme in methanogenesis
- carry C1 units along path of enzymatic reduction (methane, methanol, etc.)
methanogenesis coenzymes
Coenzyme M (last step)
Coenzyme F430 (last step-not a carrier)
Coenzyme F420 (Flavin derivative, fluoresces @420 blue-green)
Coenzyme B (terminal step, catalyzed by methyl reductase enzyme complex)
methylotrophs
oxidize methane (+ other C1 organic compounds) as electron donors
aerobic methane oxidation
CH4 -> CH3OH -> CH2O -> HCOO- -> CO2
serine pathway
acetyl-CoA synthesized from CH2O and CO2
needs 2 NADH and 2 ATP
ribose monophosphate pathway
all carbon derived from CH2O (no NADH)
1 ATP per glyceraldehyde -3-phosphate(G-3-P) synthesized
reversal of glycolysis produces glucose
anaerobic oxidation of methane (AOM)
can occur by an association (consortium) of 2 organisms: sulfate-reducing bacterium (SRB) and Archaea
RuBisCO
active in carboxysome
very low affinity for CO2 compared to O2
