Photosynthesis Flashcards
Chloroplast structure ?
- 2-10 μm diameter
- Surrounded by a double membrane envelope - each envelope membrane is phospholipid bilayer
- outer membrane is permeable to ions/small molecules
- inner membrane has transport proteins - allow certain molecules to enter/leave chloroplast
What is stroma?
Fluid filled matrix in chloroplasts (CO2,sugars,enzymes/other molecules dissolved in stroma)
What system of membranes are found in stroma?
Consists of a series of flattened fluid-filled sacs - THYLAKOIDS
(contain PHOTOSYSTEMS that contain pigments,enzymes,electron carriers)
- thylakoids stack up to form GRANA —> CREATE LARGE SA
GRANA connected by stroma lamellae
What is a photosystem?
System of photosynthetic pigments found in thylakoids of chloroplasts
- different pigment molecules arranged in funnel-like structures in thylakoid membrane
- large no. Pigment molecules in an arrangement —> MAX LIGHT ABSORBED
What does the stroma also contain?
70S ribosomes- proteins coded for by the loop of DNA produced at 70S ribosome
Loop of DNA- codes for some chloroplast proteins
Starch grains - sugars formed during photosynthesis stored as starch in starch grains
Where does each stage of photosynthesis take place?
Light dependent - thylakoids membranes of the GRANA
Light independent - in stroma
Adaptations of chloroplasts to photosynthesis?
STROMA : gel-like fluid contains ENZYMES that catalyse reactions of light independent stage
- rapid transport of products from light dependent stage as surrounds GRANA/thylakoid membranes
GRANA: Granal stacks create LARGE SA-> more photosystems can be present —> max light absorption
- more space for electron carriers/ATP synthase enzymes
DNA: chloroplast DNA (cpDNA) has genes that code for some proteins/enzymes used in photosynthesis
Ribosomes: allows translation of proteins coded by cpDNA
Inner membrane of chloroplast envelope: selective transport proteins control flow of molecules between stroma/cytoplasm of plant cell (cytosol)
2 types of pigment?
Chlorophylls (a/b)- absorb blue-violet/red regions of light spectrum
- reflect green
ACCESSORY PIGMENT: Carotenoids - absorb wavelengths in blue-violet region
- reflect yellow/orange
Why are accessory pigments useful?
They surround primary pigment + Absorb both similar/different wavelength of light to chlorophyll
- expands the wavelength range that can be absorbed for use in photosynthesis
What are the different photosystems?
Photosystem 1 (PSI) - P700
chlorophyll a which has a max absorption of light at 700nm
Photosystem 2 (PSII)- P680
Chlorophyll a has max absorption of light at 680nm
Stages of light dependent stage of photosynthesis?
- Light harvesting at photosystems
- Photolysis of water - light energy used to breakdown water —>
- ATP produced in photophosphorylation
- Reduced NADP (NADPH) produced when H+ ions in the stroma + electrons in ETC combine with carrier molecule, NADP
What is photophosphorylation?
Using light energy/electron transport chain to phosphorylate ADP to ATP
What is photolysis?
Splitting of water into H+ ions, electrons, oxygen in thylakoid lumen
2H20 —> 4H+ + 4e- + O2
Non cyclic photophosphorylation? 1-3
- Light absorbed by PSII
- 2 electrons in chlorophyll are excited to higher energy level + emitted from chlorophyll molecule —> PHOTOIONISATION
- Electron passes down electron transport chain to PSI (chain of electron carriers (proteins with Fe at centre)
Non cyclic photophosphorylation 4-6?
- As excited electrons leave PSII to PSI, they are replaced by electrons from photolysis
5.Excited electrons lose energy as they pass along ETC - this energy used to transport protons into thylakoid via proton pumps
Thylakoid has higher conc of protons than stroma- PROTON GRADIENT - Protons move down their conc grad into stroma via enzyme ATP synthase - chemiosmosis
Energy from this movement combines ADP + Pi —> ATP