Flashcards in Photosynthesis Deck (23):
1
chemical reaction for photosyntehsis
6 CO2 + 6 H2O --> c^H12O6 + 6 O2
2
what do light abosorbing pigments do
absorb energy from light which is incorported into electrons to excite them - excited e- are unstable and re-emit the absorbed energy as they fall back down, that energy is reabsorbed by e- of nearby pigment molecules; this process ends when energy is abosorbed by P680 (PSII) or P700 (PSI)
chlorophyll a, b and carotenoids
3
antenna pigments
chlorophyll b, carotenoids, phycobillins (red algae) - capture wavelengths that chlorophyll a does nt and passes energy to chlorophyll a, where the direct light reaction takes place
4
chorophyll a
poryphrin ring (alternating double and single bonds; pi bonds critical for light reactions) complexed with Mg atom
5
steps of photosynthesis
1. photophosphorylation - light dependent, produce ATP for light independent reactions to use to produce glucose
a. cyclic - PSI uses ETC between PSII and PSI to produce ATP and cycle e- back to PSI
b. non cyclic - PSII --> PSI ETC produces ATP (h2o splits w/light energy to replenish e- of PSII) and then PSI, P700 converts NADP+ to NADPH
2. light indpendent - calvin cycle, produce carbohydrates by CO2 fixation (turn RuBP to G3P, 2 G3P --> glucose)
a. alternatives = CAM or C4
6
mesophyll cell
cells in middle of leaf specialized for photosynthesis
7
why are leaves green
green is reflected, not absorbed
8
light reaction - what does the light do?
The light that is absorbed splits water into hydrogen and oxygen:
H2O + light energy ---> ½ O2 + 2H+ + 2 electrons
electrons used in ETC to produce ATP via chemiosmosis - create H+ gradient between thylakoid space and stroma (inner part)
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steps of light reaction
H2O + ADP + Pi + NADP+ + light --> ATP + NADPH + O2 + H+
1. PSII: electrons trapped by P680 are excited with light energy
2. primary e- acceptor: e- pass to the first in chain of acceptors
3. ETC: 2 e- move down chain adn lose energy that is used to phosphorylate ATP
4. phosphorylation: ATP synthase, H+ gradient used
5. PSI: ETC terminates here at P700
---noncyclic:
6. NADPH: 2e- pass down short ETC with ferrodoxin enzyme (fd) to convert NADP+ + H+ + 2e- --> NADPH (coenzyme)
7. photolysis: h2o splits to regenerate 2e- in PSII
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locations--
1. noncyclic photophosphorylation
2. cyclic photophosphorylation
3. photolysis
4. calvin cycle
5. chemiosmosis
1. thylakoid membrane - noncyclic
2. stroma lamellae (pieces connecting to thylakoid) - cyclic
3. thylakoid lumen - photolysis
4. stroma - calvin
5. thylakoid membrane - chemiosmosis
11
where are photosystems? how many?
few hundred photosystems in each thylakoid; rxn center containing chlorophyll a surrounded by antenna pigments taht funnel energy to it
12
cyclic photophosphorylation
replenish ATP when calvin cycle consumes it; excited 2e- from PSI go through ETC to generate 1 ATP, these 2 e- recycled into PSI and either take cyclic or noncyclic path from there
13
calvin cycle - dark, light independent
6 CO2 + 18ATP + 12NADPH + H+ --> 18ADP + 18Pi + 12NADP+ + 2G3P (1 glucose)
1. carboxylation - 6CO2 + 6RuBP --> 12PGA
rubisco = catalyst
2. reduction - 12ATP + 12NADPH convert 12PGA --> 12G3P (PGAL), byproducts NADP+ and ADP used in photophosphorylation
3. regeneration - 6ATP convert 10 G3P to 6 RuBP
4. carb synthesis - remaining 2 G3P used to make glucose
14
plants make glucose for their own mitochondria to use for energy; ATP in photosynthesis comes from photophosphorylation, NOT mitchondria
photophosphorylation ATP is not used for general cell fixation
15
cholorplast structure
1. double membrane (like mito and nucleus)
2. outer membrane = plasma
3. intermembrane space
4. inner membrane
5. stroma = inside of inner membrane; where calvin cycle occurs
6. thylakoid = layer in granum stacks, inside stroma -- membrane is where PSI, PSII, cytochromes are; lumen is the interior of thylakoid where H+ accumulates
16
thylakoid
a single layer of a granum (thyla = pancake; granum = stack); suspended in stroma of chloroplast - thyla membrane is where PS I adn PS II are, where ETC is
17
chemiosmosis
use H+ gradient to generate ATP;
1. H+ accumulation in thylakoid lumen
2. pH and elec gradient (pH~5)
3. ATP synthase generates ATP; 3H+ diffuse for 1 ATP
4. calvin cycle uses NADPH and ATP and CO2 to produce G3P
18
photorespiration
fixation of O2 by rubsico; no ATP/glucose -- inefficient, competes with CO2; arose when low levels of O2 --- peroxisomes breakdown products of it
19
peroxisomes in plants
break down products of photorespiration
20
alternative pathwayd
1. C4: bundle sheath instead of mesophyll to limit photorespiration
2. CAM: stroma closed during the day
21
c4 photosynthesis - hot, dry climate - minimize water loss from stomata (leaf pores) and photorespiration
purpose: move CO2 from mesophyll cells to bundle sheath cells; kranz anatomy; hatch-slack process; overcome tendency of rubsico to waste O2 in photorespiration; bundle sheath cells isolate rubsico from atmospheric O2 and saturate with CO2 by decarboxylation of malate
-all requires more ATP (1 extra, it becomes AMP)
22
steps of C4
CO2 absorbed by mesophyll cells
CO2 + PEP --> OAA (PEP carboxylase catalyst)
*CO2 is not fixed by rubisco in mesophyll
OAA-->malate; malate through plasmodesmata into bundle sheath cells
malate--> pyruvate and CO2 (pyruvate back to mesophyll, CO2 used in calvin)
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