Unit 2 - Light Dependent RXN Flashcards
Photosynthesis occurs in two stages
1) photo stage
2) synthesis stage
Photo stage
- light-dependent rxn
- occurs in thylakoid membranes in chloroplast
- energy ficing
- converts light energy to make ATP and NADPH which will be used to drive the next stage
Synthesis stage
- dark light independent rxn
(calvin cycle) - carbon fixing reactions
- uses ATP to convert inorganic mols to organic fuel containing stored potential energy in the bonds
Photosynthesis light independent / dark reaction
= calvin cycle
photosynthesis light reaction goes on to become
1) cyclic - PS1 only - makes ATP
2) noncyclic - PS2 and PS1 - makes ATP and NADPH
Summary of rxn
light - chemical energy, ATP or NADPH (through light dependent reaction) - chemical energy (through calvin cycle)
light reaction of photosynthesis can occur in 2 ways
noncyclic and cyclic photophosphorylation
both cyclic and non cyclce use chlorophyll…
which sits near an electron acceptor in a photosystem (cluster of proteins and pigments embedded in the thylakoid membrane)
Non-cyclic photophosphorylation makes
ATP ad NADPH
4 major protein complexes
1) photosystem 2 (PS2)
2) cytochrome complex (cyt)
3) photosystem 1 (PS1)
4) NADP+ reductase
5) ATP synthase
3 major electron shuttles
1) plastoquinone
2) plastocyanin
3) ferredoxin
divide 3 parts
1) photoexcitation
2) electron transport
3) chemiosmosis
photoexcitation
absorption of a photon by an electron by chlorophyll
electron transport
creates an H+ reservior
chemiosmosis
movement of protons to help phosphorylate ADP to ATP
Photoexcitation pt 1
the actions of photosystem 2 begin when a photon energizes an e- in P680 forming P680*
Photoexcitation pt 2
the energized chlorophyll (P680) then transfers the high energy e- to acceptor A in the reaction centre. P680 is now + charged
Photoexcitation pt 3
the + P680 ion then oxidized water and the high energy e- is transferred from the reaction centre to the carrier mol plastoquinone (PQ)
What has just been release and where
oxygen gas and protons r now released into the human
2water = 4H + 4e- + O2
Linear Electron Transport and ATP Synthase: 1) Oxidation of P680
the absorption of light energy by photosystem 2 results in the formation of an excited state P680 mols which is rapidly oxidized transferring a high energy electron to the primary acceptor
Linear Electron Transport and ATP Synthase: 2) Oxidation-reduction of plastoquinone
from the primary acceptor the ET to PQ which shuttles e- from PS2 to the cytochrome complex. as PQ accepts e- from PS3, it picks up protons (H+) from the stroma and then releases them into the luman as it donates e- to the cytochrome complex (H+ increases in lumen)
Linear Electron Transport and ATP Synthase: 3) ET from cytochrome complex and shuttling by plastocyanin
plastocyanin shuttles the e= from cytochrome complex to photosystem 1
Linear Electron Transport and ATP Synthase: 4) Oxidation-Reduction of P700
as PS1 absorbs additional light energy, the e- bc excited. this cause the excited e- to escape photosystem moving along a second ETC
Linear Electron Transport and ATP Synthase: 5) ET to NADP+ by Ferredoxin
first e- is transported by a sequence of carriers within photosystem 1, transferred to ferredoxin. the oxidation of ferredoxin results in the transfer of e- to NADP+ reducing to NADP
Linear Electron Transport and ATP Synthase: 6) The Formation of NADPH
a 2nd e- is transferred to NADP by another mol of ferredoxin. this 2nd e- and proton (H+) from the stroma r added to NASP by the SANP+ reductase to from NADPH
Chemiosmotic Synthesis of ATP
proton gradient is established across the thylakoid membrane by 3 mechanisms
Chemiosmotic Synthesis of ATP (1)
protons (H+) r taken into the lumeb by the redox of plastoquinone as it moves from PS2 to the cytochrom complex and back again
Chemiosmotic Synthesis of ATP (2)
the conc. of H+ inside the lumen is increased by the addition of 3 protons for each water mol that is split in the lumen
Chemiosmotic Synthesis of ATP (3)
the removal of one H+ from one stroma from each NADPH mol formed decreases the con. of H+ in the stroma outside the thylakoid
proton gradient
high conc. of ions in the LUMEN and a low conc. of ions in the STROMA
chemiosmosis
the H+ ions flow down their concentration gradient through a protein complex of ATP synthase which is embedded in the membrane releasing energy in the process
Cyclic Photophosphorylationmakes
involves PS1 only and ONLY ATP is created
Cyclic Photophosphorylation 3 major protein complexes
1)photosystem 1
2)cytochrome complex
3)ATP synthase
Cyclic Photophosphorylation 3 electron shuttles
1)plastoquinone (PQ)
2)plastocyanin (PC)
3)ferredoxin (FD)
Cyclic Photophosphorylation pathway
- uses photosystem 1 (P700) but not photosystem 2 (P680)
- electrons move in a circular pathway from P700, FD, PQ, cytochrom complex, and plastocyanin and back to P700
Products of Cyclic Photophosphorylation
- makes ATP
- make NO NADPH and O2
- calvin cycle needs more ATP then NADPH
- cyclic ET produces ATP mols needed for the redution of CO2 in Krebs
Electron Movement
photosystem 1 absorbing light energy exciting P700 to P700* gives up an electron to the primary electron acceptor and becomes P700*
P700*
receives e- from plastocyanin and returns to neural P700
e- passes through
1) ferredoxin
2) ES plastoquinone
3) cytochrome complex (pumps protons into lumen)
4) plastocyanin and then repeats
in short NONcyclic (5)
1) uses PS1 and 2
2) photolysis of water is needed
3) oxygen is evolved
4) NADPH is synthesized
5) production used for light independent rxn
in short cyclic (5)
1) ONLY PS1
2) water not needed
3) no oxygen
4) NADPH is not synthesized
5) used to make additional ATP inorder to meet cell energy demands
what is the energy of a photon first used to do in photosynthesis
energize an e-
which mol absorbs the energy of a photon in photosynthesis
chlorophyll
plants make O2 when they photosynthesize. Where does O2 come from
splitting water mols
which colours of light does chlorophyll a repeal
green
