Biology 1002B Lecture Notes - Lecture 4: Thylakoid, Chloroplast Membrane, Photosystem Ii
13 Jun 2018
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Reading Outcomes
Distinction between autotrophs (photoautotrophs) and heterotrophs.
- Autotrophs do not need to import already-formed organic compounds from the environment,
they are photosynthetic organisms
- photoautophs use energy from light to drive the conversion of carbon dioxide into an organic
form
- heterotrophs require an already-synthesized (by autotrophs) source of organic molecules to
live
Two phases of photosynthesis
- Light reactions: involve the capture of light energy by pigment molecules and the utilization of
that energy to synthesize NADPH and ATP
- Calvin cycle: the electrons and protons carried by NADPH and the energy of ATP hydrolysis
are used to convert CO2 into carbohydrate
Photosynthesis as an oxidation reduction reaction
- energy from light is used to oxidize water
- The electrons needed to reduce NADP+ to NADPH come from the oxidation of H2O ,
resulting in the release of O2
- carbon fixation is a reduction reaction, uses the electrons from NADPH to reduce the C
compounds
Structure and function of a photosystem - what do the different parts do?
- Photosystem II: harvests light & the obtained photon causes the e- from water to go to the
mobile carrier, so PSII splits water into H+ protons and O2 molecules
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- P680 (pigment) gets reduced
- Cytochrome complex (between PSII & PSI): pumps H+ protons across the gradient
- Electron Transport Chain: energized electrons lose their energy in a series of reactions
that capture the energy necessary to keep life living
Lecture 8 Outcomes
Photosynthesis: the use of light energy to convert carbon dioxide into organic compounds
Redox potential: the tendency of a chemical species to gain or lose electrons
Chloroplast: organelles found in plant cells and eukaryotic algae that conduct photosynthesis
Thylakoid membrane: inside chloroplasts, the site of the light-dependent reactions of
photosynthesis
Thylakoid lumen: the inner space of the thylakoid surrounded by the thylakoid membrane
P680: pigment in PSII (primary electron donor), absorbs light best at 680nm (+ is oxidized state,
* is excited state)
P700: pigment in PSI (reaction centre chlorophyll molecule), absorbs light best at 700nm
Chemiosmosis: the movement of protons across the
membrane in the direction of the gradient
Structure of chloroplast
- double membrane structure that contains stacks of
thylakoids called grana
- the inside of the thylakoid is called the lumen
- the stroma surrounds the grana inside the inner
chloroplast membrane
Chloroplast genome, transcription and translation
- they have their own genomes, they don’t encode for
ALL their proteins that are required, but enough that without them the organelles wouldn’t
function properly
- it has its own ribosomes, and everything you need to convert the genetic information into
protein
Structure of photosynthetic electron transport
- many proteins and many genes come together to form the complexes that are required in the
transport chain
- light harvesting occurs in the photosystems, light reactions produce NADPH & ATP which
then go on to the Calvin Cycle
- the concentration of H+ is maintained on the inside of the membrane because after they are
pumped out through ATP synthase, they get pumped back through cytochrome C (after PSII)
Source of electrons and products of electron transport
- Electrons come from water splitting, PSII removes an electron from water breaking it down
into protons and O2
- light reactions produce NADPH & ATP which then go on to the Calvin Cycle
- The main role of the light reactions is to restock the stroma with the ATP and NADPH
required for the Calvin cycle.
find more resources at oneclass.com
find more resources at oneclass.com
