2015-10-28 Lecture 16 1 Cell Biology Lecture 223.16: Chloroplasts Chloroplasts
Feb 16, 2016
2015-10-28
Lecture 16 1
Cell Biology Lecture 223.16: Chloroplasts
Chloroplasts
2015-10-28
Lecture 16 2
Chloroplasts
• Convert solar energy into ATP
Chloroplasts • Photosynthesis can be broken up into two phases or stages:
-Light reactions - Solar energy converted to ATP -Dark reactions - ATP used to fix CO2 into usable forms
Light Reactions (Stage 1) • Take place in thylakoids • Solar energy is absorbed to increase energy of electrons • Involves electron transfer which produces ATP and NADPH (and O2 as a byproduct)
used in Dark Reactions (Stage 2)
2015-10-28
Lecture 16 3
Light Reactions - Photosynthetic Pigments
1. Chlorophyll
2. Carotenoids
Light Reactions - Photosynthetic Pigments
P680 P700
Fig 14-31
Mg2+
2015-10-28
Lecture 16 4
Light Reactions - Photosynthetic Pigments
Light Reactions - Photosynthetic Pigments
2015-10-28
Lecture 16 5
Light Reactions - Photosynthetic Pigments
Each photosystem has light capturing antennae complexes (with many chlorophyll molecules) and a reaction centre that converts light E into chemical E.
In the rx centre a dimers known as a special pair hold electrons at a lower E
2015-10-28
Lecture 16 6
Light Reactions - Photosynthetic Pigments
charge separation
Photosynthesis is a biosynthetic process to build organic molecules from CO2 (the production of O2 is biproduct) The plant needs E to do this in the form of ATP and the activated carrier NADPH The plant does this using 2 photosystems (photosystem II and photosystem I) and the electron transport chain
2015-10-28
Lecture 16 7
Light Reactions and Flow of Electrons PSII (responsible for ATP II) -catalyzes the extraction of e- from water (O2 is a biproduct) -feeds e- to a proton pump leading to ATP synthesis e- transport chain (including plastoquinone) PSI (responsible for NADPH production) -final electron acceptor for the e- transport chain -three together power ATP and NADPH production e- transferred from PSII to Q to cytochrome complex (H+ pump) and eventually to PSI to Fd and then to NADP+ (which is reduced to NADPH)
H+ gradient established here fuels ATP production
*
Light boosts E of e-
Light boosts E of e-
Light Reactions - Photosynthetic Pigments
2015-10-28
Lecture 16 8
Light reactions: -Solar energy converted to ATP -Dark reactions: -ATP used to fix CO2 into usable forms
Dark Reactions • Carbon fixation reactions • 3ATP + 2NADPH are consumed • For each CO2 converted to carbohydrate • Begins in the stroma (fluid of the chloroplast) and ends in the cytosol
Light and Dark Reaction
2015-10-28
Lecture 16 9
Dark Reactions
(a 5 carbon sugar)
Dark Reactions
Final product