Week 7 Recall Questions Flashcards
On a general level, what is photosynthesis?
• Photosynthesis: Process that converts light energy into chemical energy (sugars)
• CO2 + H2O + light —> [CNH2NON) + O2
Which organisms can perform photosynthesis?
What is a technical term for these organisms?
• Plants, protists and some bacteria
(really just bacteria)
— Eukaryotes simply evolved the ability to capitalize on these bacterias invention
• specifically cyanobacteria (descendants) does photo as Endosymbionts
• Done by photoautotrophs
— Energy from light, carbon from CO2
What is a chloroplast and what structures can you find in a chloroplast (membranes, spaces)?
• Occurs in free-living prokaryotic cells or in chloroplasts in eukaryotic cells (descendants of cyanobacteria)
• In part organized on internal membrane systems that photosynthetic pigments arranged on.
— chloroplast: intern membrane separate from inner membrane = thylakoid membrane = is arranged into Granum, which are stacks of membrane structures
• inner membrane (the original bacterial membrane)
• outer membrane archaen membrane
- ex: food vacuole.
• ribosomes
• stoma
• inner and outer membrane
• thylakoid
• Granum
What are the light (dependent) reactions, what is their function?
Where do they occur?
- Photo stage of photosynthesis
- take energy from the photon of light and bind some of it in a chemical form that can be used by other processes in the cell.
- Converts solar energy to chemical energy
- Produces O2, ATP and NADP
- All proteins involved in this have to be arranged in a membrane system that allows for a buildup of gradients
- Site: thylakoid membrane
What is the Calvin Cycle, what is its function?
Where does it occur?
- Synthesis stage of photosynthesis
- other processes are this part.
- Can occur in dark + uses chemical energy from light rxns bound in ATP & NADPH (= indirectly light independent
- Requires ATP and NADPH = get from light dependent rxns
- Process of carbohydrates synthesis = converting CO2 to sugars
- Reducing C in CO2 to a more energy rich carbon compounds in form of 1st G3P, then other things.
- Site: stroma = comparable to cytosol of bacterial cell = everything outside thylakoid membrane but insider inner chloroplast membrane
- If rxn occur in stroma no longer require thylakoid membrane
What is the general function of photosynthetic pigments?
What are 3 important pigments?
Photosynthetic pigments: Pigments in chloroplasts are used to absorb light energy
Absorption spectrum: (hint: what it absorbs is the inverse of what we see)
(Main pigment)
1. Chlorophyll a
- absorbs: red/blue
- Reflects: dark green
(Accessory pigments = absorbs energy and transfer it to chlorophyll a)
2. Chlorophyll b
- absorbs: wavelengths of blue & red spectrum
- Reflects: light green
3. Carotenoids
- absorbs: wavelengths of blue/green spectrum
- Reflects: yellow, orange, red
4. Anthocyanins
- absorbs: green/yellow
- Reflects: purple, blue, red
Which pigments use resonance transfer, which one uses electron transfer?
The pigments in Light harvesting complexes use resonance. The accessory pigments
The pigment chlorophyll a pair uses electron.
Background info:
Resonance Transfer:
• Transfer/capture the energy and not electron.
— electron falls back into ground state and as does so a new pigment molecule available that takes the energy and uses it to get its own electrons excited, then that pigment’s electrons will fall back down to ground state, etc.
— Electron stays with originally atom
Electron Transfer:
• Transfer high energy electron to another molecule that acts as electron acceptor.
— have electron accepting molecule takes electron and therefore all the energy of the electron.
— Redox Rxns
What is the structure of a chlorophyll?
• porphyrin ring absorbs light/photons from sun
- a hydrocarbon component on outside part but has 4 nitrogen inside and magnesium in Center. The N and Mg Center is what captures and absorbs photons
= why plants need N in fertilizer to produce more health green leaves.
— long hydrophobic Hydrocarbon tail anchors pigment in thylakoid membrane
What is a photosystem and what are its components?
Where is it located?
• Photosystems: Light-harvesting units located in the thylakoid membrane
• Contains:
1. Several Light-harvesting complexes.
2. One Reaction-center complex
What is a light harvesting complex and what is its function?
Light harvesting complexes
Mostly pigments
• Pigment molecule absorbs photon
• Energy transferred from pigment molecule to pigment molecule by resonance transfer
• No electron transfer in antenna complexes
What is an excited electron and what are its potential fates?
When light absorbed, electrons in the porphyrin rings are excited:
• electrons moves to higher orbital in a higher energy shell
— Shells further away from nucleus are higher in energy, there electrons further away from nucleus are higher in energy
• Excited state is very unstable
• Lower energy things are = more stable they are
— So electron falls back into lower energy orbital
• 1st law of thermodynamics = energy transferred not created or destroyed
— when electron returns to lower energy state it releases some energy
• If nothing in ground state there to catch energy released 2 things can happen
- partially another photon will be released in form of fluorescence = this photon lower in energy than original photon that knocked the electron out of its orbital in the first place.
• chlorophyll is fluorescent = this one way how study chlorophyll molecules by measuring fluorescence of molecules extracted from tissues from leaves, algae etc.
- Some energy lost as heat
- Deals with 2nd law of thermodynamics = everything increases entropy of universe.
What is the reaction -centre complex, what is its function and what are the components?
Reaction-Centre Complex
Mostly protein
• Contains 1 Pair of special chlorophyll a molecules = accept energy from light-harvesting complexes
• The energy being transferred by pigment molecules of antenna complexes knocks the electrons of chlorophyll a pair into a very high orbital = electrons get so excited they get transferred to the rxn Center in form of very high energy electrons.
• chlorophyll a molecule losing electrons = oxidized
• Rxn Center complex gains electrons = reduced (charge gets reduced even tho gain electrons)
• Primary electron acceptor (rxn centre complex) accepts excited electrons from the chlorophyll a pair
What are the differences between PSII and PSI?
• Both in Thylakoid membrane
• Different composition of reaction centre complexes
Photosystem 2 (PSII)
Acts In ( first )photosynthesis
Absorbs light best at: 680 nm
Chlorophyll a pair called: P680
- P680 transfers high energy electron to primary electron acceptor (rxn centre)
Photosystem 1 (PSI)
Acts In ( second )photosynthesis
Absorbs light best at: 700 nm
Chlorophyll a pair called: P700
What is the location of the linear electron flow?
luminal face of photosystem II (PS II).
How would you describe the electron hole?
P680 chlorophyll has an electron ‘hole that must be filled by an electron donor. (After it transfers it’s electron to rxn centre)
- b/c chlorophyll lost e^- it’s very unstable = very reactive = steal e^-
Electron donor is water
• O, is released (1 0, per 2 H,O)
• H+ is released into thylakoid space and contributes to proton gradient
