Photosynthesis

Non-Cyclic Electron Flow

-Photosynthesis is the process of converting light energy to chemical energy and storing it in the bonds of sugar.

-It takes place in the chloroplasts, specifically using chlorophyll, the green pigment involved in photosynthesis.

-It occurs when the electrons from water are excited by the light in the presence of P680.

-Light energy causes the removal of an electron from a molecule of P680 that is part of Photosystem II.
-The P680 requires an electron, which is taken from a water molecule, breaking the water into H⁺ ions and O^-2 ions. These O^-2 ions combine to form the diatomic O² that is released.

-Through a series of redox reactions, the electron is transferred to an electron carrier PQ (as long as electron arrived PQ, protons are pumped in from stroma)

-Then the electron is transferred to B6F, more protons are pumped in from stroma.

-The electrons then move through PC and eventually attaching it to a molecule in Photosystem I.

- Light acts on a molecule of P700 in Photosystem I, causing an electron to be "boosted" to a still higher potential.

-The electron continues to pass through FD and FRN and eventually being attached to NADP⁺ and H⁺ to form NADPH, an energy carrier needed in the Light Independent Reaction.

-In Photosystem II, the pumping to H⁺ into the thylakoid and the conversion of ADP into ATP is driven by electron gradients established in the thylakoid membrane.

 

Cyclic Electron Flow

- Light acts on a molecule of P700 in Photosystem I, causing an electron to be "boosted" to a still higher potential.

- The electron continues to pass through FD, instead of going to FRN the electron is transferred to B6F.

-The electrons then move through PC and eventually back to a molecule in Photosystem I.

Calvin Cycle

- Glucose and other carbohydrates are synthesized in the carbon-fixing reaction of photosynthesis, often called the Calvin cycle.

- The carbon dioxide is attached to a five-carbon compound called RuBP, ribulose diphosphate, with an enzyme called rubisco.
- After carbon dioxide has been joined to ribulose diphosphate, a six-carbon product forms, which immediately breaks into two three-carbon molecules called 3-phosphoglycerate.
- ATP and NADPH₂ from the light reactions are used to convert 3-phosphoglycerate to 1, 3-phosphoglycerate to glyceraldehydes 3-phosphate, G3P, the three-carbon carbohydrate precursor to glucose and other sugars.

-One of the G3P leaves the cycle.

-The remaining 5G3P go through a series of steps to become the original RuBP.

-The cycle runs twice for make 1 glucose.