Chapter 15 - Phototrophy Flashcards
Phototrophy
Light eating - process by which energy from sun is captured and converted into chemical energy - ATP
Photoautotrophs
Used to describe organism that both convert sunlight into ATP and also use ATP to fix Co2 into organic compounds
Photoheterotrophs
organisms that convert sunlight into ATP but utilize pre-made organic compounds in the environment
Chlorophylls
Green in color (absorb red and blue, 675 nm and 430 nm). used by cyanobacteria, plants and algae.
Bacteriochlolophylls
Absorb higher wavelengths (~870 nm) than chlorophylls, allowing different phototrophs to inhabit same environment
carotenoid
absorbs blue light and shows as yellow, orange or red
phycobiliproteins - phycoerythrin
red in color
phycobiliproteins - phycocyanin
blue in color
antennae
light-harvesting pigments which funnel the light to other molecules in reaction centers
chlorosome
phototrophic pigments housed here
reaction center
perform the conversion of light energy to ATP
photophosphorylation 1
Photosystem absorbs light and funnels energy to a reaction center, specifically chlorophyll/bacteriochlorophyll molecules
photophosphorylation 2
The chlorophyll/bacteriochlorophyll molecules become excited, changing to more negative reduction potential
photophosphorylation 3
The electrons can then be passed through an electron transport chain of carriers, such as ferredoxin and cytochromes allowing for PMF.
photophosphorylation 4
Protons are brought back across the plasma membrane through ATPase, generating ATP in the process
cyclic photophosphorylation
electrons are returned to the special pair of chlorophyll/bacteriochlorophyll molecules - allows for process to be repeated over and over.
non-cyclic photophosphorylation
electrons are diverted elsewhere, and then an external electron source must be used to replenish the system.
Anoxygenic phototrophy
no oxygen is generated during process
Purple Phototrophic Bacteria
Engage in anoxygeneic phototrophy. Single photosystem with bacteriochlorophyll, allowing them to use cyclic photophosphorylation. In presence of organic compounds, operate as photoheterotrophs.
reverse electron flow
used by autotrophic purple bacteria, using the energy from the PMF to drive electrons up the electron tower.
Green phototrophic bacteria
engage in anoxygenic phototrophy and utilize a single photosystem. They also use the same system to reduce power, periodically drawing electrons off for NAD+. Require external electron donor. Operate as photoautotrophs.
Oxygenic Phototrophy
used by cyanobacteria containing chlorophyll a, with two distinct photosystems, each with a separate reaction center.
What does oxygenic phototrophy allow for?
generation of both ATP and reducing power in one process
Z Pathway 1
Light energy decreases reduction potential of chlorophyll a in photosystem II
Z Pathway 2
Electrons are then passed through an electron transport chain, generating ATP via PMF
Z Pathway 3
Electrons then passed to photosystem I (PSI) where they get hit by another photo of light, decreasing their reduction potential even more.
Z Pathway 4
The electrons are then passed through a different ETC, eventually being passed off to NADP+ for formation of NADPH
Rhodopsin-based Phototrophy
used by archaea - unusual - no use of chlorophyll or bacteriochlorophyll. Instead of bacteriorhodopsin. When this is absorbs light, it undergoes conformational change, pumping proton across cell membranes and development of PMF.
bacteriohodoposin/archaeorhodopsin
a retinal molecule related to one found in vertebrate eyes
