Happens in the grana of chloroplasts
Light (energy) gets trapped by chlorophyll pigments (light energy converted to chemical energy) This energy used to turn ADP and Pi into ATP
Energy used to split water (H2O) into Hydrogen and Oxygen
The hydrogen ions get collected by NADP, which becomes NADPH The Oxygen is waste, and leaves!
So, in this stage, water comes in.
ATP and NAPDH come out, as does Oxygen.
2. Light independent stage (Carbon Reduction)
Happens in the stroma of the chloroplast.
It’s the Calvin Cycle
At the start of the cycle, there’s a 5 Carbon molecule RuBP A CO2 molecule enters and attaches to it, making a 6 Carbon molecule Rubisco is the enzyme that makes this happen.
That’s not stable, so that 6C molecule splits into two 3C molecules (PGA) The PGA molecules are “reduced” by NADP to form PGAL
This takes energy; ATP turns back into ADP
PGAL, a 3C molecule, is a starting point for glucose (off to the cytosol…) Other PGALs are used to make RuBP, and it starts again…
If 6 CO2 come in, and get added to 6 RuBP, that makes 6 of the unstable 6C molecule. When that breaks down, you get 12 PGA molecules.
Those 12 PGA molecules, after NADPH and ATP do their thing, become 12 PGAL molecules. 2 of those PGALs go off to the cytosol to form glucose. (2x3C will make one 6C glucose) 10 of the PGALs (3C each remember = 30C) form 6 RuBP (5C molecules…6x5 =30!) So it takes 6CO2 coming in to end up with a glucose…
BUT, actually only one CO2 gets dealt with at a time, so it takes 6 turns of the cycle to end up with a glucose…
Briefly? CO2, NAPDH, ATP come in.
Glucose, NAPD, ADP come out.
C3 plants are called that because carbon reduction begins with the 3C molecule PGA. C4 plants have a step before the Calvin cycle, where a step occurs in mesophyll cells to make a 4C compound. This compound gets transported to cells around vascular bundles deeper in the plant. The 4C compound gives up a CO2, which then Calvin Cycles in the usual way. Because the CO2 has effectively been moved deeper in the plant, the concentration gradient is steeper, and the plant therefore picks up CO2 more quickly than C3 plants (mesophyll cells closer to the outside air than vascular bundles). So C4 plants better in hot/dry areas where the plant doesn’t want the stomata open for too long- best it picks up its required CO2 very quickly!
In the cytosol
Glucose, a 6C compound, is broken into 2 pyruvate molecules (a 3C compound) Hydrogen is released during this, and picked up NAD, which becomes NADH (2) 2 molecules of ATP are also formed.
2. Krebs cycle
Matrix is the space enclosed by the inner membrane of mitochondria. Cristae are the compartments made by the (highly folded) inner membrane of the mitochondria. Krebs cycle occurs in the inner compartment (matrix) of mitochondria. Pyruvate comes in, and gets converted to other things.
For each pyruvate, 3 CO2 are formed.
More “carriers” accept hydrogen (and electrons): 4 NADH, 1 FADH2 Acetyl co-enzyme A is an intermediate product.
2 ATP are formed.
3. Electron Transport
Happens on the inner membrane of mitochondria
There are compounds called cytochromes involved.
NADH and FADH2, (carrying electrons) are brought in.
The electrons from these molecules are transferred from one cytochrome to another. Electrons final accepted at the end by oxygen, which becomes negatively charged O2- The charged O2- reacts with H+ to form water
32 molecules of ATP are formed (sometimes 34)
Overall: glucose and oxygen come in, water and CO2 go out.
36-38 molecules of ATP formed.
Carrier molecules are formed, then release their load (NAD etc.)
Happens in the cytoplasm
Glycolysis produces pyruvate
In animals, pyruvate then gets converted to lactate
When oxygen is again present, the lactate can be converted back to pyruvate. In yeast, pyruvate undergoes fermentation, producing ethanol and CO2.