Tuesday night video review:
[thylakoid disk——-> stack of thylakoid disks——-> granum] = light dependent reactions
[stroma —–> outside the thylakoid] = light independent reaction 0r Dark Reactions
“we are just using them for their hydrogen..haha…we take the hydrogen off them and chuck the oxygens away.”
12 H2O —–> 24 H+ (hydrogen ions/protons) + 24 NADP+ ——-> 24 NADPH——> light dependent reaction 18 ATP produced ————————————–> light dependent reaction (no ATP leftover for anything other than the light dependent reaction
inside thylakoid ——–> stroma
24 hydrogens ripped of water eventually become 6 H2O (12) and 1 C6H12O6 (12)
6 carbons from 6 CO2 become 1 C6H12O6 (glucose)
18 ATP + 12 H2O (l) + 6 CO2 (g) ———> 6 O2 (g) + C6H12O6 + 6 H2O
made from sunlight roots uptake stomata (pores) waste concentrated energy
ΔG = ? ΔSuniv = ?
Is energy coupling occurring here?
What did he leave out? (electrons!)
Graham Walker, PhD (MIT professor)
Cyclic Photophosphorylation – Preceded Respiration – 3.4 BYA
“sunlight kicks an electron up to higher orbital and when it is in a higher orbital it is easily lost”
“chlorophyll absorbs a particular wavelength from sun but this embedded in a multi-protein structure that has a bunch of other molecules that absorb at different wavelengths and then funnel that energy into the one that chlorophyll comes in.”
“When chlorophyll absorbs energy (the electron) goes up to an excited state ..and now is in a higher energy state (father away from the protons in the nucleus) and is more easily removed. “It is so easily removed that it actually becomes a strong reducing agent – (itself gets oxidized but helps other GAIN electrons).
In this diagram Dr.Walker is diagraming the thermodynamic pathway of the electrons!
High free energy ——-> Lower free energy
Excited electrons less energetic
During this free fall Free Energy by excited electrons are used to pump H+ into the thylakoid. This creates an electron gradient (high concentration of H+ ) which is another form of Free energy that is used to create 18 ATP!
So Free Energy of the Sun ——-> Free Energy of the High H+ concentration ———> ATP
So Free Energy of one form is being converted to free energy of another. So what must be released in each step?
And this 18 ATP in Cyclic Photophosporlation is used by the prokaryote cell to drive life sustaining reactions. The low energy electrons are returned to the chlorophyl.
“there are still bacteria that exist today that still use Cyclic Photophosphorylation”
“ATP is not enough to take carbon dioxide and make into sugars or carbon compounds. We need a source of reducing power as well … Remember that CO2 is the most oxidized form of carbon.
||Notice the electrons in double bond of Carbon (C) are being pulled away from the C (carbon) toward the oxygen (O). Because Oxygen is the element that has the one of the greatest attraction for electron (its the reason it is such a small atom) AND this oxygen is BONDED ON BOTH SIDES of the molecule, Carbon “kind of” has its valence electrons removed or lost. This “kind of” loss is oxidation.
These ancestral organisms used H2S to as a source of reducing power AND NADP+ to gather the reducing power for biosynthesis (making sugars, etc).
H2S + NADP+ ———————–> S + NADPH + H+
“The key is to get CO2 down to a more reduced form of Carbon”
It was done by using the reducing power of NADPH and the ATP made.
Non- Cyclic Photophosphorylation – 3.0 BYA – (Current Photosynthesis)
In Noncyclic Photophosphorylation the electron that were excited by chlorophyll are used to generate a proton force in the same way as cyclic BUT these electrons ARE the ones that are the source of reducing power when they combine with NADP+.
Why is it an improvement over the Cyclic?
“it uses the energy of the sun to make ATP (like Cyclic) BUT it also uses energy of the sun to make NADPH!”
“So in other words, this second version gives the cell simply from the energy of the cell everything it needs to take carbon dioxide (CO2) and make it into organic (carbon based compounds).
It gives it the energy to reduce CO2!
||The Noncyclic process accomplishes this by using a second photosystem that reenergizes the electrons that were just used to pump H+ into the thylakoid. Once re-energized by the absorption of energy by the sun ( in the second photosystem, photosystem I) the electron is now at higher energy state that can reduce NADP+. This electron is not returned to Photosystem II.
In this current process, since the electron does return to the original photosystem it must get another electron from another source. That of course is water.
2: Photosynthesis diagram – Cyclic vs Noncyclic Photo phosphorylation , Diagram
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