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Phototrophy and photosynthesis
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Terms in this set (46)
What is phototrophy?
The ability of a cell/microbe to capture light and use it to synthesize ATP and generate reducing power.
What is photosynthesis?
When ATP and reducing power derived from light energy are used to reduce and fix CO2. Divided into two parts (light reactions and dark reactions).
What are the three main types of phototrophy?
Oxygenic photosynthesis (uses chlorophyll)
Anoxygenic photosynthesis (uses bacteriochlorophyll)
Rhodopsin-based phototrophy (used by photoheterotrophs)
What do phototrophs use to generate proton motive force?
What is photo-phosphorylation? What does it require?
The process of synthesizing ATP from proton motive force derived from light.
Requires light-absorbing pigments.
What do chlorophyll pigments trigger when they absorb light?
Electron flow down the ETC, which leads to the establishment of PMF.
What are rhodopsin pigments?
Light-driven proton pumps that directly form PMF.
What is produced and released when light energy is converted to chemical energy?
What organisms utilize chlorophyll?
Photosynthetic eukaryotes and cyanobacteria.
What two wavelengths of light does chlorophyll absorb?
650 nm (red) and 430 nm (blue)
What is the side chain in chlorophyll used for?
Attachment to a membrane (thylakoid membrane in eukaryotes).
What is an antenna?
A highly organized array of chlorophyll pigments that create a large surface area that traps a maximal quantity of photons (300 chlorophyll molecules/antenna).
Where does light energy absorbed in antennas get transferred too?
Reaction-center chlorophyll pairs (directly involved in electron transport).
What is the function of the antenna in photosystem I?
It absorbs light of longer wavelengths and funnels light to the RCCP called P700.
What is the function of the antenna in photosystem II?
It absorbs light of shorter wavelengths and funnels light to the RCCP called P680.
What happens when light energy is transferred to P700? What does it do with the energy?
It becomes excited, causing it to inherit a highly negative reduction potential. It donates excited, energy-rich electrons to a series of carriers (terminal acceptor is ferredoxin).
What is cyclic photophosphorylation?
In photosystem I, after P700 donates its electrons to the carriers, it can receive these electrons again at the end of the chain, exciting it and restarting the process. All the while, PMF is established and can generate ATP.
What is noncyclic photophosphorylation?
In photosystem I, after P700 donates its electrons to the carriers, the carriers sequentially reduce each other until ferredoxin (Fd) is reduced, which then donates its electrons to NADP+, forming NADPH.
What happens when light energy is transferred to P680? What does it do with the energy?
It becomes excited, causing it to inherit a highly negative reduction potential. It donates excited, energy-rich electrons to a series of carriers in the ETC. ATP is generated from this process. Additionally, electrons at the end of the chain are used to reduce oxidized P700.
How is oxidized P680 reduced?
It is reduced when water is used to donate electrons (this creates oxygen as a biproduct).
What are the light reactions of oxygenic photosynthesis? What do they produce?
Oxidative photosynthesis (photosystems I and II). They generate ATP and reducing power (for dark reactions).
Where do the light reactions take places?
They occur in membranes:
Eukaryotes: thylakoid membrane (separates thylakoid lumen and stroma)
Cyanobacteria: thylakoid membrane in cytoplasm
What molecules are required to reduce one molecule of CO2 to a carbohydrate (CH2O)?
3 ATP and 2 NADPH.
What are the main inputs and outputs for noncyclic photophosphorylation?
Input: 4 electrons
Output: 2 NADPH, 2 ATP.
How many photons are required to fix one molecule of CO2?
What are the main differences between oxygenic photosynthesis and anoxygenic photosynthesis?
Molecules other than water are used as electron sources.
They use different photosynthetic pigments (bacteriochlorophylls).
They have one photosystem.
Bacteriochlorophylls are the RCCP's.
What is the difference between oxygenic/anoxygenic photosynthesis and rhodopsin based phototrophy?
They use rhodopsin as their light-absorbing pigment.
Does not use electron transport chain (generates proton gradient by translocating protons into periplasmic space via pigment).
What is anabolism?
The synthesis of complex molecules from simpler molecules using energy input and reducing power.
What are the six principles of governing efficient biosynthesis?
Polymers are made from monomers.
Enzymes operating in amphibolic pathways can have reversible functions.
Enzymes operating in amphibolic pathways can sometimes only function in one direction.
Anabolism requires energy.
Physical separation of catabolism and anabolism.
Using different cofactors for catabolism and anabolism.
What are polymers made from?
What is an amphibolic pathway?
A reversible metabolic pathway that can do anabolism and catabolism.
What does using enzymes in amphibolic pathways for just one direction allow for?
Independent regulation of the two directions of the pathway.
What function do precursor metabolites serve? What modifications are made to them?
They provide the carbon skeleton for biosynthesis. Functional groups are added to them in the synthesis process.
Where are precursor metabolites produced in chemoorganotrophs that utilize glucose?
They are produced in glycolytic pathways and in the TCA cycle.
How are precursor metabolites produced in autotrophs?
They convert CO2 into organic carbon. They then use this carbon to generate precursor metabolites through the central metabolic pathways.
What is CO2 fixation? What does it require?
The conversion of CO2 into organic carbon. It requires input energy and reducing power.
What is the most common CO2 fixation pathway?
The Calvin cycle (reductive pentose phosphate pathway).
Where does the calvin cycle take place?
Eukaryotes: stroma of the chloroplast.
Cyanobacteria: carboxysome inclusions.
What are the three phases of the calvin cycle?
What is the function of RubisCO?
It catalyzes the addition of CO2 to the 5C molecule RuBP.
What occurs during the carboxylation phase of the calvin cycle?
RubisCO catalyzes the addition of CO2 to the 5C molecule RuBP, which forms 2 molecules of PGA.
What occurs during the reduction phase of the calvin cycle?
PGA gets reduced to glyceraldehyde 3-phosphate by oxidizing NADPH to NAD+ and by cleaving ATP into ADP.
What occurs during the regeneration phase of the calvin cycle?
RuBP gets reformed, allowing the cycle to repeat itself. During this process, multiple carbohydrates (used as precursor metabolites) are produced. This phase uses 1 ATP.
How many times must the calvin cycle occur to produce on molecule of glucose?
6 times. This is because each turn of the calvin cycle produces one molecule of glyceraldehyde 3-phosphate.
What are the inputs of the calvin cycle?
What are the outputs of the calvin cycle?
18 inorganic phosphate
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