photosynthesis Flashcards
photosynthesis
light energy from the sun is used to synthesized glucose
overview of photosynthesis
- chlorophyll A,B + carotenoids absorb energy from sunlight
- photons excite electrons
- excited electrons are unstable and re-emit energy
- energy absorbed by chlorophyll A molecules, P680 (PSII) + P700 (PSI)
what does chlorophyll A have?
porphyrin ring with Mg2+ atom inside
chloroplast anatomy (8)
intermembrane space
outer membrane
inner membrane
granum
thylakoid lumen
stroma
stroma lamellae
thylakoid membrane
granum
stacks of thylakoids
thylakoid lumen
location of photolysis
H+ ions accumulates here because of the ETC
stroma
location of the calvin cycle
stroma lamellae
location of the cyclic photophosphorylation
thylakoid membrane
location of the ETC
structure which absorbs light
light reaction
- electrons trapped by PSII are energized by light
- 2 excited electrons are passed to a primary electron acceptor and move through the ETC
- these 2 electrons lose their energy which is used to form ~1.5 ATP
where does the ETC end
PSI»_space; electrons are re-energized and passed to a different primary electron acceptor which can now go through the cyclic or non-cyclic path
cyclic phosphorylation
- 2 electrons from PSI go back through the 1st ETC and generate 1 ATP
- these 2 electrons are recycled into PSI and can either go through cyclic or non-cyclic pathway again
non-cyclic phosphorylation
- 2 electron go through an ETC and combine with NADP+ and H+ to form NADPH
- this NADPH is used in the calvin cycle to create glucose
dark reaction is also known as
calvin cycle
what is purpose of dark rxn
fixes carbon dioxide into glucose
CO2»_space; 2 G3P
4 steps of dark rxn
- carboxylation = 6CO2 + 6RuBP»_space; 12PGA
catalyzed by enzyme RuBisCo - reduction = 12 PGA (with 12 ATP + 12 NAPH)»_space; 12 G3P or 12PGAL
byproducts NADP+ & ADP go to non-cyclic photophosphorylation - regeneration = 10 G3P (with 6 ATP)»_space; 6 RuBP
- carbohydrate synthesis = remaining 2 G3P used to form glucose
is calvin cycle light dependent or independent
independent
requires high energy molecule NADPH and ATP produced in the light rxn
action spectrum
chloroplasts are highly effective at absorbing red and blue light
green wavelengths are reflected making it least effective at photosynthesis
photolysis
H2O splits into 2H+, 2e-, and 1/2 O2
2H+»_space; NADPH formation
2 e- lost in PSII is replenished through this process
1/2 O2»_space; released as gas
where does photolysis occur
PSII
chemiosmosis
uses H+ gradient to create ATP
in chemiosmosis where does H+ accumulate
in the thylakoid membrane
1. H+ released into the lumen through photolysis
2. between PSII and PSI, cytochromes bring H+ into the lumen from the stroma»_space; this creates pH and electrical gradient
ATP synthase uses a gradient to…
turn ADP into ATP
this ATP is used in calvin cycle to create glucose
where does chemiosmosis occur
thylakoid membrane
alternatives to C3 photosynthesis (there are 2)
C4 photosynthesis
CAM photosynthesis
C4 photosynthesis
- alters location of photosynthesis
- CO2 moved to bundle sheath cells to minimize photorespiration and H2O loss
- produces an intermediary 4-carbon compound and uses 1 extra ATP
CAM photosynthesis
- alters timing of photosynthesis
- fixes CO2 at night instead of day to minimize photorespiration and H2O loss
