photosynthesis Flashcards
photosynthesis
provides metabolic energy, raw materials and oxygen
calculated to produce a lot of sugar per year.
chloroplast
- surrounded by double membrane
- inside is called the stroma, which is the basal material
- complex set of membranes called thylakoid membranes
thylaoid
comes in stacks, which are hollow, and have passages. These stacks are called granum….
four places for reactions in chloroplast
- stroma: soluble rxns
- Inner thylakoid fluids: soluble rxns
- Grana: membrane bound rxns
- other membranes: membrane bound rxns
chlorophyll a
- most common and abundant type
- in cyanobacteria, algae, plants
- main thing that harvests light
- found in all algae including cyanobacteria
structure of chlorophyll a
- long hydrophobic chain (anchor)
- 4 cross linked nitrogen
- magnesium in center
- side groups
- porphyrin ring
light absorbance spectrum of chlorphyll a
lots of absorbance at 430 and 662
chlorphyll b structure
- only in green algae and plants
- similar in structure to chlorophyll a, with a CHO- group added
chlorphyll b absorbance
absorb at 453 and 642
chlorophyll c structure
- no tail
- not in green plants, found in diatoms, dinoflagellates, brown algae
- has porphyrin ring, no hydrophobic chain
chlorophyll c absorbance
- blue light
chlorophyll d
- in cyanobacteria and red algae, no terrestrial plants
chlorophyll d absorbance
- infrared light strongly
- infrared can penetrate water
carotenoids
- accessory pigments in light harvesting complexes
- antioxidants
- stabilize protein folding
- quench ROS
- thermally dissipate excess energy
phycobilins
- water soluble
- cyanobacteria and red algae
what happens when pigment absorb light:
electron boosted to high energy level (photoexcitation) can do one of three things:
1. fluorescence, can fall down to lower E level, gives off a light color
2. resonance electron transfer, energy can be transfered from one thing to another until it reaches chlorophyll a
3. high energy e- can be captured, and displaced
reactions for photosynthesis
3 CO2 + 6 H2O to give C3H6O4 + 3 O2 + 3 H2O
Very little glucose is produced right away.
light dependent rxns
aka energy transduction rxns, as light rxns may be misleading.
- produce ATP and NADPH
- will not occur without light
light-independent rxns
aka carbon fixation rxns
- use ATP and NADPH to fix C and produce organic compounds
light dependent rxns details
- highly complex, harness light energy
- many pigments, enzymes, proteins
- precise configuration is crucial
- take place on thylakoid membrane
- two photosystems, each with antenna, complex and rxn center
photosystem 1 location
- on outer part of thylakoid stacks and the channels between grana
- exposed to stroma
PS 1 structure of rxn center
boosts P700 to high energy , associated with Ao e- acceptor molecule, then passed along cytochrome chain from Ao to A1, then iron sulfur proteins, then ferredoxin to cytochrome b (transmembrane complex, spans thylakoid membrane) then finally, sends to plastocyanin
PS 1 function: cyclic PP
- cyclic photophosphorylation going from high lvl P700 to low lvl P700… replace themselves.
- Cyt b fills thylakoid with protons to give a + charge. Proton gradient is used to make ATP
PS1 function : NonCyclic PP
goes through a different pathway to make NADP into NADPH… which is 3x the E of ATP… no way back from here, so the cant happen unless there are e- to replace it.
PS II location
- located within thylakoid membranes
structure of PSII
- excited P680, accepted by pheophytin, passed to Qa then Qb then to cytochrome b (proton gradient)
- takes in water and releases Hydrogens and electrons to replace the ones we have lost in the NC PP OF PS1.
PSII NC PP
light strikes PS II c, boosts P680 e- to high lvl, captured by pheophytin and passed down ETC to Qa and Qb, at the same time water is splitting to replace e- and produce H+ and O2 is the waste product. e- are passed to PSI and boosted again as P700. Then passed through cytochromes to make NADPH. This is NC because it never cycles back.
Why do plants have PS I
need both going for photosynthesis to be balanced
C3 pathway
carbon fixation.
Complex set of rxns; CALVIN CYCLE must cycle 6 times.
begin with rubisco, combines with RuBP, makes 3PGA (C3 pathway)
rubisco
abundant in plants. massive amounts in leaves. Captured CO2 in the leaf and combines with RuBP to make a 6 C molecule
Reduction pathway
reduces PGA to GA3P, produces ADP and NADP from NADPH and ATP, and Pi also released
glyceraldehyde production
GA3P is produced after GA3P
Regeneration pathway
Ga3P to RuBP, and Pi + ADP produced
photorespiration
Rubisco’s AS which grabs CO2, can grab C and O which is a problem.
Normally would make PGA, but can also go through oxygenase activity to produce phosphoglycolate which is useless.
C4 pathway
- PEPCarboxylase in mesophyll cells
- forms OA
- OA to Malate
- Malate moves to bundle sheath cell
- Malate decarboxylated to Pyr, CO2 to Calvin (broken in bundle sheath cell)
- Pyr transported back to mesophyll cell
C4 anatomy
- mesophyll cells: well-developed grana (light-capturing)
- bundle-sheath cells: little or mo grana, much starch
- Kranz (wreath) anatomy
C4 energetics
- C3 pathway: 3 atp
c4: 5 atp
Advantages of C4 pathway:
- PEP carboxylase binds to bicarbonate, not to O2 so no photorespiration in mesophyll (most important)
- anatomy minimizes overall photorespiration and CO2 loss
- more efficient at higher temperatures
- conserves water (due to not having to open stomata much)
- higher net rates
- lower N requirements
CAM pathway
- uses C3 + C4 , separated temporally
- used by many arid plants: succulents, cactus, orchid, stonecrop, welwischia, quillwort, some ferns
CAM pathway at night
- cooler, stomata open, CO2 enters mesophyll cells
- PEP carboxylase fixes CO2 to produce OA
- OA reduced to malate, stored in vacuole
CAM pathway during day
- hot, stomata close to conserve water
- malate decarboxylated, CO2 enters calvin cycle (rubisco)
anatomy of CAM plants
- ## spongy mesophyll leaves
advantage of CAM
- strongly conserves water
- photosynthetic capacity is limited during the day, slow growth
