Photosynthesis Flashcards
What is ATP
ATP is an energy carrier
Adenosine triphosphate
Energy from light is stored when ADP is phosphorylated to form ATP
ATP is hydrolysed to ADP & Pi -> 30.6 kJ
Energy released is used for:
- Movement of organelles (vesicles, centrioles, chromosomes)
- Active transport (proton pump, endo,exo,pino,phagocytosis)
- Formation of chemical bonds (translation, form DEOXYRIBONUCLEOSIDE TRIPHOSPHATE, ATP converted to cAMP (cell signalling)
Photosynthesis
Light energy converted to chemical energy (absorbed by photosynthetic pigments)
Light-dependent rxn
- thylakoid membrane, light energy req.
Light-independent rxn Calvin Cycle
- Stroma, light energy not directly required
Chloroplast structure
Consists of:
Outer, Inner, thylakoid membrane
Outer & inner enclose stroma
Thylakoids form stacks, Grana
Feature & function of chloroplast envelope
Outer & Inner membrane
Compartmentalisation & specialisation of chloroplast for p/s
Feature & function of thylakoid membrane
- Grana, many flattened coin like stacks 600nm diameter
- Intergranal lamellae, sheet like w narrow space
Where light dependent rxn occurs
- Large SA for attachment of multiple photosystems electron carriers, proton pumps & stalked particles
- Photosystems & electron carriers are closely located & arranged in sequential order
- Phospholipid bilayer IMPERMEABLE to protons, allowing accumulation of protons, creating PROTON gradient
Feature & function of stroma
Circular DNA, 70S ribosomes, gel-like medium w. soluble enzymes, organic acids, sugars & lipids, ATP,ADP,NADP
Site for light independent Calvin Cycle
Closely associated w. thylakoid membranes,
products of light d channnelled to light ind
Temp storage of starch
Light dependent rxns
Directly dependent on light intensity
In thylakoid membrane
1. Photoactivation of chlorophyll
2. Photophosphorylation
Purpose of light-dependent
Synthesis of ATP & NADP, O2 byproduct
Photosystems (Light D)
2 types, I & II
Made up of Light harvesting complex + Reaction Centre
- Chlorophyll a (pri pigment, directly)
- Light harvesting complex:
- Chl b (accessory, absorbs & transforms to a)
- Carotenoids (absorb wavelengths a cannot) - Rxn centre
- pair of a moleq, a680, a700 use light energy to excites 1 e- to a higher energy lvl
- Pri e- acceptor to capture excited e- from special chl a & becomes reduced
PS1 -> chl a700 pigment
PS2 -> chl a680 pigment
Electron carriers (Light D)
Electron transport chains: Found on thylakoid membrane
Sequence of electron carrier moleq of progressuvely lower energy levels
- Transport e- thru redox rxns from higher to lower energy levels
- As e- move from 1e- carrier to the next, energy is released
Proton pumps (Light D)
Harness energy released from e- transport chain to pump H+ from stroma into thylakoid space against conc. gradient via ACTIVE TRANSPORT
Proton gradient across thylakoid membrane drives ATP synthesis
NADP reductase (Light D)
Membrane bound enzyme that catalyses the formation of reduced NADP/NADPH from NADP+
NADPH produced used as RA in light ind rxn
Stalked particles/ATP synthase (Light D)
Enzyme catalyses synthesises of ATP using H+ gradient
ATP produced in Light Ind (Calvin Cycle)
1. Transmembrane hydrophilic proton channel, allows Facilitated Diffusion of H+ down conc. gradient from thylakoid space to stroma
2. ATP synthase head; rotates, harnesses proton-motive force to synthesise ATP from ADP and inorganic phosphate
Photoactivation (Light D)
Light energy absorbed by accessory pigments, passed from 1 pigment to anotheruntil the pair of a special chl a moleq reaction centres P680 PSI & P700 PS II
Light energy excites an e- of each special chl a moleq to a higher energy level, leaving chl a +ve charged, excited e- captured by the pri e- acceptor
Photophosphorylation (Light D)
Synthesis of ATP from ADP & Pi using Light energy in photosynthesis via CHEMIOSIS
1. Cyclic
2. Non-cyclic
Non-cyclic photophosphorylation
Involves PSI & PSII
1. Photoactivation occurs
2. e- absorbed by pri e- acceptor, passed along chain of e- carriers & proton pumps in ETC of progressively lower energy levels
3. energy released by H+ pumps to transport H+ from stroma into thylakoid space against conc. gradient via active transport ->proton gradient
4. H+ ions move from thylakoid space back into stroma thru ATP synthase via FD down conc. gradient
5. e- flow down ETC from PSII to PSI combine w NADP+ & H+ -> NADPH (Light D rxn)
[Catalysed by NADP reductase]
PSI receives replacement of e- from PSII
PSII receives replacement of e- from photolysis of H2O producing e-, H+ & O2 hence H2O is electron dono for non-cyclic
Cyclic phosphorylation
PSI only
e- are returned to photosystem but still generate ATP
1. Photoactivation occurs:
- Light energy absorbed by accessory pigments of PSI
- light energy passed via accessory pigments to special chl a in P700
- excited e- emitted from special chl a & transferred to pri e- acceptor
- Excited e- passed along chain of e- carriers & pron pumpsin ETC of progressively lower levels via redox rxns, passed back to special chl a in P700
- Energy released used to transport H+ from stroma into thylakoid space agaisnt conc. gradient via active transport - H+ move from thylakoid space back into stroma via ATP synthase via FD down conc. gradient
- ATP synthase harnesses proton-motive force to generate ATP from ADP & Pi (Chemiosis)
- ATP generated used in Calvin cycle
Cyclic VS non cyclic
Cyclic:
PSI only
enzyme: ATP synthase only
e- donor: special chl a PSI
flow: cyclical e- flow from special chl a back to special chl a
Doesnt involve phtolysiss of water
Special chl a in PSI is final e- acceptor
ATP as product
Calvin cycle/light ind:
Occurs in STROMA
Uses ATP & NADP, depends on light d rate
Calvin cycle (enzymes) rate depends on
- CO2 conc
- Temp
Contains 3 stages
1. CARBON FIXATION
- 1 moleq CO2 combines w 5C RuBP (ribulose biphosphate) to give 6C intermediate
- Catalysed by RUBISCO
- Unstable intermediate breaks down to 2 PGA (3GP)
- PGA(GP) reduction
- Each PGA molecule receives 1 extra phosphate from ATP to form [glycerate 1,3 biphosphate]/[1,3 biphosphoglycerate]
- glycerate 1,3 biphosphate reduced by NADPH, loses phosphate grp to form GALP(TP) glyceraldehyde 3 phosphate (triose phosphate) - Small proportion of GALP produced exits Calvin cycle, used as starting material for organic compounds
- Majority of GALP remain in Calvin cycle, used to regenerate RuBP. ATP from light d provides energy & phosphate for rearrangement of carbon atoms to regenerate 5C RuBP
- ADP & Pi recycled for light d
