mechanics of photosynthesis

[galleon]

Inspired by Johnny's quest for lighting truth, I typed this very rough sketch of photosynthesis up in hopes it may benefit some of the members of the board through better understanding of the dynamic capabilities of the organisms they keep.

Structure:
Organelles (cell structures performing specific life functions) called chloroplasts are the sites of photosynthetic activity. In generalized terms, the chloroplast is a double membraned structure. The stroma is the large central space encompassed by these membranes. In the stroma, stroma lamella (connective structures) link grana together. Grana can be thought of as cylindrical tubes (each having an individual membrane, and within, photosynthetic pigments, ie chlorophyll), containing disk shaped sacs called thylakoids (each has an individual membrane, and a vacuole like space within, facilitating ion transport).

Process:
At the business end of the chemical equation for photosynthesis (ie, the product of the reactants), when simplified by a factor of six (with the factor of six, the product is that word everyone remembers, or would like to forget, from high school biology; glucose, along with 6 O2) is carbohydrate (CH20) and oxygen (O2). How do you get there from light, water and Carbon dioxide? Good question... Start at the beginning: Photosystem II (I know, I know...lol). Photosystems I and II are particles contained within the inner area (Photosystem II) and outer area (Photosystem I) of the thylakoid membrane. These particles must contain antennae (pigment complexes containing hundreds of photosynthetic pigment/chlorophyll molecules), an electron acceptor and an electron donor. Think of Photosystem II as a funnel that has an antennae. The antennae of this Photosystem only "tune in" to specific energy levels of light radiation. The antennae absorb light energy, which in the case of Photosystem II is a very high amount of energy, exciting the electrons of the pigment complexes as it moves down the complex-filled "funnel", and electrons actually leave the valence shell of the photosynthetic pigments. This is where water comes in. A negatively charged electron from the water molecule replaces those oxidized from the chlorophyll molecule from being excited by electromagnetic (light) energy. This splitting of water gives off gaseous oxygen... this is where the primary productivity of photosynthesis hobbyists have heard so much about comes from. At the end of our Photosystem II funnel lies an acceptor molecule, or "reaction center", to which loose cannon electrons are passed. This reaction center passes them through a transport system. As it passes through this system, it looses energy. This lost energy becomes the victim of chemiosmosis, where hydrogen ions collect in the thylakoid space, setting up a gradient down which hydrogen ions flow, reacting with an as yet unidentified ATP synthesizer contained in the thylakoid membrane, forming ATP (ATP, adenosine triphosphate, is broken down to ADP, adenosine diphosphate, and P, phosphate for cell processes).

Subsequent to exiting the transport system, the electrons are absorbed into Photosystem I, which tolerates less energy than Photosystem II due to differing photosynthetic pigments. Some electrons have already evacuated Photosystem I, due to light energy absorbed. These electrons, along with a hydrogen ion from teh chemiosmosis of the transport system, will form NADPH from NADP (nicotinamide adenine dinucleotide phosphate, a transferring coenzyme of electrons). The electrons from the transport system, arriving from Photosystem II replace those lost to NADPH formation. The synthesis of ATP and and NADPH is know as photophosphorylation. Cycling Photophosphorylation occurs when some electrons are not handed over to NADP, instead these select electrons return to the transport system to form more ATP, justified by higher cell function energy need. Exact ecological circumstances initiating cylcing photphosphorylation are as yet unknown (probably the best theory is when CO2 must be highly budgeted).

The products of photophosphorylation, NADPH and ATP, are necessary to reduce carbon dioxide (CO2), which takes place in the stroma, where energy bonds carbon with hydrogen (and takes up electrons) using several enzymes, thus the end product formed is carbohydrate, CH20. The necessary reactants to reduce CO2 (energy and hydrogen) are supplied by NADPH and ATP. CO2 is taken up by a sugar, RuBP (ribulose biphosphate). This transforms RuBP from a 5-carbon molecule to a 6-carbon molecule, which instantaneously divides into twin molecules of PGA (phosphoglycerate). Using all of the produced NADPH and some of the ATP, PGA is reduced to PGAL (phosphoglyceraldehyde). PGAL is used for two specific functions. First, it, and remaining ATP are utilized within the organelle to reform RuBP, and second, the rest is stacked up in net gain. However, a specific ratio of use to net gain is not known, and probably varies. Each two PGAL from the net gain combine to form that magic little thing we call glucose! (well, more correctly glucose-phosphate). Now here is where Jerel's favorite term, "metabolic pathways" comes in. Photosynthetic organisms have the capability to convert glucose phophate by metabolic pathways (via enzymes) to every type of organic molecule they could ever want! Pretty slick, huh?

[MontanaRocknReefer]

Chris I thank you for our chat yesterday in the Chat Room about lighting and believe I have a better understanding of what the reef requires as far as artificial lighting in a reef aquarium and what natural sunlight is all about in trying to obtain as close to nature what a wild reef and sunlight need in relationship to one another. Thanks again. Johnny

[Drew]

Wow Chris, very impressive! Maybe you should give this to Brooke. It would make for a great article when the new pages get up. I am thoroughly impressed!

Drew

[Doug1]

tagged for archives, as always thanks
to quote jimmy Cliff ....................

[galleon]

Drew, lol, I wouldn't be surprised if I blurt out photosynthesis related things like "ribulose biphosphate" in my sleep... It's that well committed to memory. lol.

[Grimmy]

Whoa, this brings back memories of taking all of this in since I am a Bio Sci major. I can see electrons being transfered to a higher excited energy level as a wavelength of light hits the P780 photosynthetic molecule... gee its good to know I can get something out of my major and the 4 years weren't a complete waste..hehe

[galleon]

(nudges Grimmy with elbow and whispers) "don't you mean P680?" Photosystem II antennae is P680 (680 nm for chlorophyll a ), Photosystem I antennae is P700 (700 nm for cholorophyll a). (BTW, for everyone, those are just maximum wavelengths the antennae pigments can absorb, the "P" stands for pigment)

[Drew]

jeez Grimmy (any relation to Frank Grimes?), mixing up P780 photosynthetic molecule with P680 photosynthetic molecule. I mean, how much more simple does it need to be!?!?!?!?

[galleon]

ha ha ha



ROTFL
Chris

[Spanky]

Photosynthetic organisms have the capability to convert glucose phophate by metabolic bathways (via enzymes) to every type of organic molecule they could ever want!

BINGO

WOOGA WOOGA


Carbon is carbon, that's been the point all along.

Chris, thank you for writing this, and thank you for waking me up and making me read it.

Also, thanks in advance for not letting me use it as a weapon.

[galleon]

Also, thanks in advance for not letting me use it as a weapon.

...and what makes you think I'm gonna stop you? ...as long as you dish out the royalties, that is...
ROTFL.
Chris

[Grimmy]

Sorry i couldn't remember, but I could have swore that there were also other different types of chlorophyll a, b, c that did absorb a variety of wavelengths so organisms didn't have to heavily rely of that certain wavelength. There are other minor wavelengths that are captured, but yet I believe I stand corrected on the two Photosystems.

Gee....I guess I should dig out and consult all my notes that I have from my plant physio course before I add any additional comments to this post. Otherwise I might get flamed!

[Martyn]

Thanks for the info a tad tricky for me too take it all in but some diagram's would be great.
Can it be explained with diagrams for idiots like me or is that impossable.

Martyn

[sculpin]

If you really want an interesting read, try looking at the same pathways at the atomic level. Photosynthetic reaction centers aren't particles. They're huge and devilishly complex.

[galleon]

They're huge and devilishly complex.

(shudders) yep...I hear you. "Mommy; I'm a photosynthetic reaction center in this year's school halloween play. Here are the pieces to my custume. *whomp* I need it by...tomorrow." I just wrote up a very rough "sketch" of what happens in photosynthesis though, hence the intro, lol.

Martyn, if you can get your hands on any college level biology text, especially a newer one, they usually have very nice and spelled out diagrams of structure and process.
Chris