Lecture 14: Photosynthesis Flashcards
How much energy from sunlight hits a square meter of Earth’s surface per day?
~3.5-7.0 kWh/m^2
What are the three processes used by bacteria to generate energy via photosynthesis?
- Electron independent ATP generation
a. produces ATP - Cyclic electron transport
a. produces ATP - Linear electron transport
a. produces ATP
b. & NADPH
What are the three processes used by bacteria to generate energy via photosynthesis?
- Electron independent ATP generation
a. produces ATP - Cyclic electron transport
a. produces ATP - Linear electron transport
a. produces ATP
b. & NADPH
What are the 3 key compounds capable of absorbing light energy?
- Carotenoids
- Chlorophylls
- Bilins
Contain a “chromophore”
a. can absorb light E and transfer into
electrons
How do rhodopsin proteins aid energy generation for bacteria and archaea?
- Transmembrane protein
- Central carotenoid capable of absorbing
light E (e.g., retinal) - Causes conformational change (e.g.,
goes from all-trans-retinal to 13-cis-
retinal) - Causes release of proton (e.g., from
Lys residue and then past to Asp to
release inside) - ESSENTIALLY A SIMPLE FORM OF
PROTON PUMP - Creates proton motive force
What is “photoheterotrophy”
Make energy through photosynthesis and respiration
What carotenoids do most photosynthetic organisms use? What’s the difference between them?
- Chlorophyll a
a. absorbs light most at ~410 and
680nm - Chlorophyll b
a. Abs. light most at ~460 and 630nm - THE ONLY DIFFERENCE
a. Aldehyde group
b. Has methyl group
What is purple non-sulfur bacteria?
- Utilize chlorophyll carotenoids
- Belong to “Rhodospirillaceae group”
(Alphaproteobacteria) - Include:
a. Rhodobacter sphaeroides
b. Rhodopseudomonas palutris - Can grow aerobically in dark by respiring
on organic carbon sources
What are purple sulphur bacteria?
- Belong to groups:
a. Chromatiaceae
b. Ectothiorhodosiraceae - Can tolerate high sulphur environments
- STRICTLY ANAEROBIC
- Must fix CO2 to survive
a. Utilise the “reverse tricarboxylic acid
cycle (TCA)”
How can purple bacteria absorb infrared light?
Absorb INFRARED LIGHT via BACTERIOCHLOROPHYLLS
1. Light hits: "Light harvesting complex
2" (LH2)
a. large complex containing
bacteriochlorophylls (abs. infrared
light)
2. Passes E onto LH1
a. circular array of proteins
b. central "Reaction centre (RC)"
3. LH1 passes E onto RC
4. RC can use energy to:
a. Excite an electron
b. Pass electron onto ubiquinone (UQ)
c. UQ passes electron onto
cytochrome bc1 complex - pumps
protons across membrane
d. Electron passes onto cytochrome c
to be passed back to the RC
CYCLIC ELECTRON TRANSPORT
How do purple bacteria use their energy?
- Fix carbon dioxide into sugars
a. Carboxysome inside the cell (high
[CO2])
b. Fixation occurs using rubisco
c. Can be done with nitrogen also
How does fixation of nitrogen and CO2 occur in purple bacteria?
1. Requires an electron donor (Hydrogen
sulphide / H2S)
a. restricts where they can survive
2. Electron arrival at RS
3. e- passed onto ferredoxin
4. e- can then be passed to either:
a. Nitrogenase: N2 -> ammonia (8e-)
b. Ferredoxin NAD(P)+ reductase:
NAD(P)+ + H+ -> NAD(P)H (2e-)How does fixation of nitrogen and CO2 occur in purple bacteria?
1. Requires an electron donor (Hydrogen
sulphide / H2S)
a. restricts where they can survive
2. Electron arrival at RS
3. e- passed onto ferredoxin
4. e- can then be passed to either:
a. Nitrogenase: N2 -> ammonia (8e-)
b. Ferredoxin NAD(P)+ reductase:
NAD(P)+ + H+ -> NAD(P)H (2e-)What are green sulphur bacteria?
- Only anaerobic
- V. low light environments
- E.g., Chlorobiaceae
- Utilise “CHLOROSOMES”
a. Stacks of bacteriochlorophyll c
b. layer of bacteriochlorophyll a
c. sit on a base plate connected to
plasma membrane and reaction centre
What’s the problem with using reduced sulphur compounds for source of e-?
Limited to environment
