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Day 20, Photosynthesis Light Reactions (Slide 3, The Steps - 1 (-A photon…
Day 20, Photosynthesis Light Reactions
Slide 3, The Steps - 1
-A photon of light strikes a pigment molecule, boosting the energy of its electron
-The energy is transferred to various pigment molecules, until it reaches the P680 pair of chlorophyll a molecules
-The energy here raises the electron to a higher energy state
Slide 1, The Light Dependent Reactions
-The light dependent reactions require light to occur
-Lights major role is to energize electrons within the chloroplast
Slide 5, The Calvin Cycle
-The Calvin Cycle takes place in the stroma
-The Calvin Cycle does not re quire light
It is referred to as the ‘Light Independent Reaction’ or the ‘Dark Reactions’
-The Calvin Cycle fixes CO2, by incorporating it into an organic molecule (glucose) that can be used by organisms
Slide 8, Step 3 Synthesis
-Two of the 3 Carbon molecules are removed and used to make sugars, lipids, proteins, etc.
-This leaves Ten 3 Carbon molecules
Slide 9, Step 4 Regeneration of RuBP
The ten remaining 3 carbon molecules are converted back into six 5 carbon molecules (RuBP)
The cycle will then begin all over again
Slide 2, Photosystems
-Photosystem – a protein complex surrounded by light harvesting complexes
-In the light reactions there are two photosystems, and two electron transport chains (ETC’s)
~Photosystem II
~ETC
~Photosystem I
~ETC
Slide 6, Step 1 Carbon Dioxide Fixation
-6 Carbon Dioxide molecules enter the Calvin Cycle
-The CO2 molecules combine with six 5 carbon molecules known as RuBP (Ribulose Bisphosphate)
-Requires the help of RuBP Carboxylase (RuBisCo)
-The result is twelve – 3 carbon molecules called 3 PGA (3 phospoglycerate)
Slide 7, Step 2 Carbon Dioxide Reduction
-Energy from ATP and electrons from NADPH turn the 3 carbon molecules into high energy 3 carbon molecules
-The byproducts are ADP and NADP+
The Steps – 2 & 3
2.The electron is transferred from P680, to the primary electron acceptor
P680 turns into P680+
3.An enzyme splits water molecules into 2 electrons, two hydrogens, and an oxygen
~Electrons will go 1 by one to P680
~Oxygen atoms will bond with another oxygen atom (from another H20) to form O2
The Steps – 4 & 5
4.Each photo-excited electron passes from the acceptor in PSII to PSI via an electron transport chain (made of the molecules Pq, A cytochrome complex, and Pc)
5.The electron here loses energy, and the energy is used to pump protons (H+) through ATP Synthase to produce ATP’s
The Steps - 6
-Light comes into PSI, and acts in a similar way as it does in PSII
-The electron will go to the primary electron acceptor in PSI, and P700 will become P700+
-Electrons are eventually passed to NADP+, which is reduced to NADPH by NADP Reductas
Slide 10, In Closing
-The Calvin cycle uses ATP and NADPH from the light reactions
-After its done, it gives the NADP+ and ADP back to the light reactions to start all over again
-The production of Glucose is the main purpose of the Calvin Cycle
-3 Phosphoglycerate can go on to make many other molecules depending on what the organism needs.