Gilmour - Metabolic Diversity of Microbes Flashcards
describe bacteriarhedopsin’s (BR) morphology and energy production system
simplest photosynthetic system
single protein light driven proton pump
found in halophilic archaea
a homologue proteorhodopsin found in marine proteobacteria
energy production system:
- 7 alpha helices span membrane
- surround retinal molecule linked to lysine
- photon absorbed by retinal => trans - cis
- relaxation to trans pumps H+ across mem
- uses F1F0 ATP synthase
Which bacterium forms a purple membrane with BR?
Halobacterium salinarium
Which wavelengths does BR absorb?
Green, reflects blue and red (appears purple)
Which other method of metabolism does BR use to supplement organoheterotrophic mode of growth?
photoheterotrophy
Which photosystems does oxygenic photosynthesis use
PS1, PS2
Describe the steps of oxygenic photosynthesis
energy from photoexcitation of chlorophyll
- photolysis of H2O
- e- to ETS
- O2 = product
Light absorbed by PS2 (P680) & PS1 (P700)
Produce H+ grad and NADPH
Use of F1F0 ATP synthase
Which photosystems are used in anoxygenic photosynthesis? Which general pigment is used?
Either PS1 or PS2
Bacteriochlorophyll
Why does bacteriachlorophyll absorb red light more strongly?
There is less energy in the far red end of the spectrum which means no photolysis (anaerobic)
Infrared penetrates further in water
Describe anaerobic PS1 photosynthesis
Found in chlorobia ‘green sulphur’ bacteria
use far red to separate e- from H2S/organic e- donor (succinate)/Fe2+
e- + NAD(P)+–>NADPH
bacteria also generate H+ grad => ATP synthesis
describe anaerobic PS2 photosynthesis
found in alphaproteobacteria ‘purple nonsulphur’
uses low infrared energy which separates e- from bacteriochlorophyll
e- to ETS; e- returned to bacteriochlorophyll;ATP generated by cyclic photosythesis
PS2 has no direct way to make NADPH therefore must use ATP to drive reverse e- transport to make NADPH
describe the principle of lithotrophy
energy required by oxidation of inorganic e- donors
reduced inorganics can be e- acceptors to and ETC with a terminal e- acceptor (TEA) that is a strong oxidant (O2/NO3-)
(inorganics are relatively poor donors
give the equation for nitrogen oxidation
NH4{+}+0.5O2–>NH2OH+O2–>HNO2+0.5O2–>HNO3
give the equation for sulphur and metal oxidation and the environmental issues this causes
H2S+0.5O2–>S+0.5O2–>0.5S2O3{2-}+O2+H2O–>H2SO4
causes environmental acidification
problem made worse by iron:
FeS2+14Fe3{+}+8H2O=15Fe{2+}+2SO4{2-}+10H{+}
give the equation for dehalorespiration (a type of hydrogenotrophy) and state an application
C2Cl4+4H2–>C2H4+4H{+}+4Cl{-}
(form of anaerobic resp.)
can be used in bioremediation
give the equation for methanogenesis and the domain that implements it
CO2 + 4H2 –> CH4 + 2H2O
Performed by archaea (methanogens) and provides niches for methanogens
which two forms of lithotrophy can also be classed as anaerobic respiration?
dehalorespiration and methanogenesis
what makes anaerobic respiration anaerobic?
not using O2 as the terminal electron acceptor
which 3 common terminal electron acceptors can bacteria and archaea use instead of O2?
NO2-, NO3- and fumarate
in a given environment the strongest electron donor and acceptor are chosen, what happens to the other potential donors/acceptors?
they are repressed
what does a negative reduction potential indicate about the species?
that the reverse reaction ie the loss of electrons (oxidation) yields energy
what does a positive reduction potential indicate about the species?
the forward reaction ie the gain of electrons (reduction) yields energy
what does a positive change in reduction potential indicate about the Gibbs free energy?
its negative and therefore is a spontaneous reaction in the forward direction
(a negative reduction potential indicates the reaction is spontaneous in the reverse direction, however this can’t be used to produce electricity)
describe the steps of aerobic respiration
electron from organic substrate donated to initial oxidoreductase (molecule which accepts one e- from one molecule and donates e- to another molecule)
e- transferred to quinone pool
quinol (QH2) e- transferred to terminal oxidase (Cyt bo)
during e- transport 8H+ moved across membrane (pmf)
what can pmf power other than ATP synthesis?
flagella movement/uptake nutrients/efflux toxic drugs
biosynthesis/anabolism is the building of complex molecules, what 3 things does it require?
essential elements/redox power (NADPH)/energy via coupling reaction (eg ATP synthesis/pmf)
which 4 organisms perform the calvin cycle?
oxygenic phototrophic bacteria
chloroplasts in algae/plants
facultatively anaerobic purple bacteria
lithotropic bacteria
describe the calvin cycle
3x Ribulose 1,5 bisphosphate + 3CO2 (and rubisco)
=> 6x 3-phosphoglycerate
=> 6x glyceraldehyde-3-phosphate (G3P)
=> 1G3P => glucose
=>5G3P => 3x ribulose-5-phosphate (via sugar phosphate intermediates)
=> 3x Ribulose 1,5 bisphosphate (start of cycle)
what is the purpose of the calvin cycle?
CO2 fixation
why is it important for CO2 to be concentrated around Rubisco? Why is this difficult?
rubisco has a low affinity for CO2 and its efficiency is further decreased by competition with O2 (photorespiration). difficult to manage as CO2 readily diffuses
how is CO2 concentrated in cells to rubisco?
carbon concentrating mechanism
- CO2 HCO3{-} using carbonic anhydrase
- HCO3{-} can be stored in membranes
which genes are expressed when CO2 conc is low and when it is high?
low conc CO2: ndhF4/ndhF3/sbtA/cmpA
high conc CO2: ndhF4 (constitutive expression)
what is the purpose of the reverse TCA cycle?
assimilation of small quantities of CO2 via regenerating the intermediates of TCA cycle (anaplerotic reactions)
what is the purpose of the reductive TCA cycle in some archaea and bacteria?
reduction of CO2 to regenerate acetyl-CoA and build sugars
how many ATP and CO2 are used in the reductive TCA cycle? which moleclues are used for reduction?
The reductive TCA cycle uses 4–5 ATPs to fix 4 molecules of CO2 and generate one oxaloacetate. Reduction done by NADPH or NADH and by reduced ferredoxin (FDH2)
state the steps of the reverse/reductive TCA cycle
oxaloacetate => malate => fumarate => succinate => succinyl-CoA + CO2 => 2-oxyglutarate + CO2 => isocitrate => citrate => oxaloacetate (cycle repeats)
acetyl-CoA + CO2 => pyruvate => phosphoenolpyruvate + CO2 => oxaloacetate
what is the name of the specialised cell that aquatic cyanobacteria use to fix N2?
heterocysts
which 2 domains can fix N2?
some archaea and bacteria
how are anaerobic conditions maintained?
photosynthesis is ‘turned off’
give the equation for nitrogen fixation and state how many ATP are consumed
N2 + 8H{+} +8e{-} + 16ATP => 2NH3 + H2 + 16ADP + 16Pi
(2e- require 3ATP equivalents)
requires 28 ATP
which enzyme catalyses nitrogen fixation? how many reductive cycles are required to fix nitrogen?
nitrogenase
4 cycles
state the 4 steps in nitrogen fixation
Fe protein accquires 2e{-} (from electron transport protein) and transfers them to FeMo centre
FeMo centre + 2H{+] => reduced H2 gas
N2 displaces H2
successive pairs of H+ and e- reduce:
N2 --> HN=NH --> H2N--NH2 -->2NH3
2NH3 + 2H+ --> 2NH4+
