Chpt 19 Flashcards
Structure of Chloroplast
3 membrane layers:
- Outer
- Inner
- Thylakoid-thylakoid membrane organized into stacked (appressed) and unstacked regions (Nonapressed). Stacked regions are called grand
3 compartments:
- Intermembrane space
- Stroma
- Thylakoid lumen
Chloroplast Function
1) Photosynthesis-reduces Carbon dioxide to carbohydrates
2) Synthesizes
- amino acids
- fatty acids
- lipids
3) Reduce nitrate (NO2-) to ammonia (NH3)
4) Storage of pigments, starch, and lipids
What do plastids develop from?
Proplastids- small undifferentiated organelle present in early plant development
Plastid Development
Proplastids->Etioplasts-> Plastids
Plastids are classified by:
- Presence/absence of thylakoid membrane
- type of pigment
- type of material stored
Types of plastids?
1) Chloroplasts
2) Chromoplasts
3) Leucoplasts
Chlorplasts
- Presence/absence of thylakoid membrane
- type of pigment
- type of material stored
TYPE OF Plastid
- thylakoid membranes
- pigment-chlorophyll
- carry out photosynthesis-don’t store anything
Chromoplasts
- Presence/absence of thylakoid membrane
- type of pigment
- type of material stored
Type of Plastid
- lack thylakoid membrane
- pigment=carotenoids-pigment of flowers
- functions (other than color) unknown
Leucoplasts
Type of plastid
- lack thylakoid membrane
- no pigments present
- storage of energy molecules
2 Types:
1) Amyloplasts
- starch storage
2) Elaioplasts
- lipid storage
Photosynthesis
6CO2 + 6H2O ->C6H12O6 + 6O2
1) Light reaction in thylakoid membrane that synthesizes ATP and NADPH
- Photosystem II (PSII)-P680
- Photosystem I (PSI)-P700
Noncyclic flow of electrons (PSII and PSI)-synthesis of ATP and NADPH
Cyclic flow of electrons (PSI only)-synthesis of ATP only
2) Dark Reaction (Calvin cycle) in Stroma
- reduces carbon dioxide to carbohydrates
Complexes of Light Reactions
Photosystem II (PSII)
- PO (plastoquinone)
- cyt bf (cytochrome bf)
- PC (plastocyanine)
Photosystem I (PSI)
- Fd (ferredoxin)
- Fd-NADP+ reductase
- ATP synthase
Photosystem II function
1) splits water to hydrogen and oxygen
- 4H+ released into thylakoid lumen
- 1 O2 released into thylakoid lumen
- 4 e- used to reduce 2Q to 2QH2
2) energizes electrons using solar energy (Photon)
3) establishes proton gradient which is used to synthesize ATP
Platoquinone function
small lipid soluble protein that transfers electrons from PSII to cyt bf
-redox state cycles from plastoquinone (Q) to Plastoquinol (QH2-reduced) back to plastoquinone (Q)
plastocyanine function
transfers electrons from cyt bf to PSI
Photosystem I function
- electrons are reenergized by solar energy
- NADP+ reduced to NADPH
Ferredoxin function
Transfers one electron from PSI to Fd-NADP+ reductase
Fd-NADP+ reductase function
reduces NADP+ to NADPH
- FAD accepts 1e- and 1H+ from 2 Fd (2e- and 2H+ total)
- transfers hydride (H-) to NADP+ which picks up H+ from stromal side of thylakoid membrane to synthesize NADPH
ATP synthase function
phosphorylates ADP To ATP using energy harnessed from the proton gradient
NON cyclic flow of electrons
Water-> PSII-> Q-> cyt bf->PC-> PSI-> Fd-> Fd-NADP+ reductase-> NADH
produce NADPH in addition to ATP due to proton gradient
-both ATP and NADPH end up in stroma
pH of stroma
8
Cyclic Flow of electrons
PSI-> Fd-> Q-> cyt bf-> PC-> PSI
Produces ONLY ATP (NO NADPH)
Chlorophyll a and b
-structure
substituted tetrapyrole (like heme)
- pyrrole-> N complexed to Mg2+
- conjugated polyene-alternating single/double bonds
Phytol-hydrophobic 20 Carbon tail
Chlorophyll a and b differ by one functional group
- A-Methyl
- B- formyl group
Chlorophyll a and b
-function
captures photon of light in the reaction center
-chlorophyll a and b have different wave lengths of light
Carotenoids
-structure
conjugated double bond system
Carotenoids
-function
- absorb light between 400-500 nm
- Provides yellow and red colors of fruit and flowers- chlorophylls a and b are destroyed allowing the carotenoids color to show
Reaction center
pigments (chlorophyl a and b and carotenoids) in/on ct thylakoid membrane absorb photons of light and transfer energy to the reaction center containing a special pair of chlorophyl a molecules
Organization of Photosynthetic complexes
- PSII located in stacked regions
- PSI and ATP synthase located primarily in unstacked regions
- Cyt bf located in both stacked and unstack regions
- Plastoquinone (Q) and Plastocyanine (PC) transfer electrons from different regions
Photosystem II structure
Transmembrane complex of thylakoid membrane
-Contains “special pair” P 680-contains two chlorophyll molecules bond between core subunits D2and D1
Photosystem II electron flow
- 2 H2O
- Mn2+ center
- P680-> Chlorophyl A-special pair
- Qa-bound
- Qb-soluble
Heart of Photosystem II is?
Manganese Center
Mn2+ center Structure
contains 4 Manganese-that exist in 4 different oxidation states (2,3,4,5)
- 1 calcium
- Tyrosine called Z
Mn2+ Center function
activates 2 H2O molecules
- allowing oxidation (electron extraction) by the special pair (P680) forming 1 O2+ 4H+ + 4e-
- the electrons are moved one at a time
S1->S2->S3->S4->S5->S0
How many photons of light is required to form one O2
4 photons
cytochrome bf
-structure
Transmembrane complex of thylakoid membrane Four subunits -cytochrome with two b type hemes -Rieske center Fe-S protein -Cytochrome F with a c-type cytochrome
Homologous to complex III it uses THE Q CYCLE
cytochrome bf
-function
uses energy harvested from electrons to transfer protons into thylakoid lumen
Plastocyanin
-structure
small, soluble copper containing protein on the luminal side of the thylakoid membrane
Photosystem I
-structure
Massive transmembrane complex of thylakoid membrane
-contains special pair P700 held between major subunits psaA and psaB
Photosystem I electron flow
Pc-> P700-chlorophyll A special pair-> Ao-chlorophyll->A1-quinone-> 4Fe-4S-> Fd
Ferredoxin Structure
- Soluble protein on stromal side of thylakoid membrane
- contains 2Fe-2S
Ferredoxin-NADP+ structure
Transmembrane flavoprotein of thylakoid membrane
-Contains FAD as prosthetic group
Light Harvesting Complex II (LHC-II)
structure
abundant ct membrane protein
binds:
- 7 chlorophyl a molecules
- 6 chlorophyl b molecules
- 2 carotenoid molecules
Light harvesting complex II (LHC-II)
-function
funnels energy from photons of light to reaction center
Calvin cycle (Dark Reaction)
Catalyzed by Rubisco (Ribulose bisphosphate carboxylase) and other enzymes
- occurs in stroma
- uses ATP and NADPH from light reaction
- reduces carbon dioxide to carbohydrates
