Bioenergetics III: phototrophy Flashcards
Explain what are retinal based protein pumps (phototrophs)
retinal is a pigment that absorbs light for phototrophs so that they can acquire energy from it
where is retinal pigment that absorbs light contained in for Archaea and Bacteria respectively
Archaea: housed in bacteriorhodopsin
Bacteria: housed in proteorhodopsin
how do Retinal-based proton pumps work?
- sunlight energy activates retinal. allowing rhopsin to push protons out of the cell
-this forms a proton gradient! which can be used to generate ATP
How does the anoxygenic photosystem I work?
- photosystems are chlorophyll based.
- in photosystem I, the organism takes electrons from an electron donor.
- sunlight energy activates photosystem I, allowing it to push electrons up the tower of power.
- electrons fall down the tower to reduce NAD+ to NADH.
- NADH can be used in the cell (reducing power).
how does anoxygenic photosystem II work?
- photosystems are chlorophyll based
- in photosystem II, sunlight energy is used to strip electrons from bacteriochlorophyll (P870) and push them up the tower of power.
- NOT ENOUGH PROTON ENERGY TO REDUCE NAD+ DIRECTLY
so…
electrons are transferred through the electron transport chain, generating PMF
PMF is used to power the forward electron flow, generating ATP.
PMF is used to reverse electron flow to generate NADH from NAD+
What is the Oxygenic Z pathway (aerobic PS II + PS I).
PHOTOSYSTEM II
- photosystem II strips electrons from H2O, forming oxygen.
- sunlight energy arriving at PSII pushes the electrons up the tower
- electrons move down the electron transport chain, generating ATP
PHOTOSYSTEM I
- electrons are transferred to photosystem I
- sunlight energy arriving at PSI pushes the electron up the tower
- High-energy electrons are used to generate NADH.
in one sentence, what do photosystems do?
Photosystems push electrons up the tower, so that they can fall back down again and generate more ATP or PMF (used for ATP).
What is the Calvin-Benson-Bassham Cycle
- to prevent wasteful photorespiration, cells performing the calvin cycle often have CARBOXYSOMES , organelles that let in carbon dioxide and keep out oxygen.
what is the reductive (reverse) TCA cycle?
- it is like the TCA cycle but backwards.
- very common in anaerobic autotrophs.
what is the 3-hydroxyproprionate bi-cycle
- it is only found in green sulfur bacteria… but maybe others
- first attempt at anoxygenic autotrophy
what is the 3-hydroxyproprionate/4-hydroxybutyrate cycle
- it is uniquely an archaeal pathway
- incredibly efficient: requires ATP to produce the same amount of precursor metabolite or biomass.
what is wood-Ljungdahl (reductive acetyl-CoA) pathway?
- uses HYDROGEN as an electron donor and carbon dioxide as the electron acceptor
- moving electrons up the redox tower: requires energy input
- But… energy is conserved! the cycle generates a PMF (or sodium motive force) that can be used to produce ATP.
Wood-Ljungdadhl (reductive acetyl-CoA) pathway
KEY ENZYME:
results in:
used by what kinds of microbes?
KEY ENZYME
- carbon monoxide dehydrogenase
RESULTS IN:
- acetate production
ANAEROBIC
- used by acetogens and methanogens.
in heterotrophs, the carbon source must get across the cell membrane.
what are the two main concepts?
- carbon sources in the environment exist on a continuum of solubility, which distinguishes dissolved organic matter (DOM) from particulate organic matter (POM)
- some molecules can be transported across the cell membrane, some cannot.
define osmotrophy:
consumption of dissolved organic matter (DOM) that diffuses or is actively/passively transported across the cell membrane.
