Lecture 1/29 Flashcards
What do we know of current bacteria diversity?
Photosynthesis is assembled from bacteria components that evolved through a process of endosymbiosis and lateral gene transfers.
What were the main points in the nature paper “Biomarkers evidence for green and purple sulfur bacteria in stratified Paleoproterozoic sea”?
What they did:
Looked at a set of rocks, crushed them and extracted the organic matter in liquid organic fractions.
What they found:
Found membrane components ->helped point out what bacteria were there.
Found pigments -> eg carotenoids, IMPT bc part of the photochemistry and metabolism was able to ID through the pigments to a set of bacteria.
Overall, was able to reconstruct the ecology of the ocean 2.5 Ma.
Who was CB Van Niel and what was this contribution?
Dutch biochemist. And he came up with the general equation of photosynthesis. He connected that photosynthesis was a life process connected to a redox process.
What is anoxygenetic photosynthesis?
Process by which energy is obtained from light but does not produce oxygen.
Most organisms use sulfur as their e- donor.
What is photosynthesis?
The biochemical process by which light is absorbed and converted into chemical energy, ultimately resulting in the reduction of carbon dioxide to organic carbon.
Occurs in two steps: Light reactions and carbon reactions.
What does light drive in anoxygenic photosynthesis?
Only the light reactions are driven by light.
What does light drive in oxygenic photosynthesis?
The reducing power that drives the carbon reactions is driven by light.
Light splits 2 waters, releasing oxygen.
This is bc it was two photosystems -> twice the power -> can split water
What are the main differences in anoxygenic photosynthesis?
- Evolves many times and first
- Primarily in bacteria
- Gain reducing power from environmental sources, usually reduced sulfur
- Pigments and apparatus are integrated into cytoplasmic membrane
- Produces oxidized compounds (eg SO4^2-)
What are the main differences in oxygenic photosynthesis?
- evolves once (no later than 2.5 Ma)
- evolved in cyanobacteria into eukaryotes
- Gain reducing power from splitting water, which is ubiquitous but difficult to split
- Pigments and apparatus are found in chloroplasts, separate organelles
- Produces oxygen gas (O2)
Why are plants green?
Pigments reflect parts of the EM spectrum they don’t absorb.
Thus, chlorophyll does not absorb green, so organisms with chlorophyll appear green
How does a plant cope with excess energy?
- Fluorescence
- Heat
- Energy transfer
- Photochemistry
How is light absorbed?
Light is absorbed by pigments
What are the main photosynethetic pigments? Their parts?
Chlorophylls.
They have a tail and head (which was a porphyrin ring).
Tail is anchored to a membrane and the head is where excitation occurs.
How do pigments absorb different wavelengths?
Small differences in the functional groups change absorbance wavelengths.
-huge diversity
What are the three main chlorophylls in cyanos and euks?
Chlorophyll a, b and c
What organism has chlorophyll a and chlorophyll b?
Cyanos, green algae, and terrestial plants
A+ B = GREEN
what organisms have chlorophyll a and c?
Red algae
A + C = RED
What are the accessory pigments? What do they do?
Carotenoids and bilins are accessory pigments: they absorb light and energy. Carotenoids form a protective function. (Act as sunscreen, reason why leaves turn red)
Bilins help generate energy in cyanobacteria.
But chlorophylls are the ones doing all the activity.
What are antennae complexes?
Aka light-harvesting complexes (LHC).
- Many pigments together act as antennae - they are arranged spatially in order to obtain as much energy.
- receive proton, get excited into a higher energy, then pass it to where the redox reaction occurs through resonance transfer.
- no chemical reactions occur here
- LHC are arranged around reaction centers
What are reaction centers? What happens there?
This is where chemical reactions take place.
Energy gets turned to ATP
In what direction does energy go?
Energy can only move towards the reaction centers, not away from it. Only downhill the energy gradient towards the reaction centers.
What makes a photosystem? If there a difference between anoxygenic and oxygenic photosynthesis in regards to their PS?
Antenna complexes + reaction center = Photosystem
; light is absorbed by the pigments in PS
Anoxygenic photosynthesis there is one photosystem harvesting the light and doing the redox rxns.
Oxygenic photosynthesis there are two photosystems acting as one.
Why are photosystems important in an evolutionary sense?
Comparing the biochemistry of different photosystems give us deep insight into how photosynthesis evolved.
Where are the antenna complexes and reaction centers embedded? Why?
Antenna complexes and reaction centers are embedded in membranes where they can be close to key complexes and set up a proton gradient.
This is then used to generate ATP
