| MadSci Network: Biochemistry |
Hi Catrina! Great question!
ATP formation in mammalian mitrochondria takes place by a complicated electron transport pathway. The structure of the mitochondia is largely defined by an outer and inner membrane. The inner mitochondria membrane is where you find all of these components of the electron transport pathway.
Electrons generated by the dehyrogenation of NADH or succinate are transferred from one complex to another until they reach complex IV, also known as cytochrome oxidase. (The high energy NADH comes from the TCA cycle and glycolysis, which in other words means from the processed food that we eat.) Here, the electrons are used to reduce oxygen into to water. ATP is produced as a result of the passage of electrons through complexes I, III, and IV.
ATP production in plants is quite different. Plant have chloroplasts, which you can think of as being like mitochondria in mammals. These chloroplasts use chlorophyll to catalyse photosynthesis, which ultimately does the following two reactions:
The high energy NADPH gets used in other metabolic pathways. The oxygen gets released, to possibly be breathed in my mammals for their own ATP formation. Finally, the extra protons build up in chloroplast organs called thykaloids and make a proton gradient. An ATP synthase, which operates without any light, then couples the flow of protons to ATP synthesis.
When I say coupled, I mean that the enzyme somehow makes it so that for every three protons which flow out of the thykaloid, one molecule of ATP gets made.
By the way, this is a great example of the inherant energy available in a concentration gradient, which can be converted in chemical energy used in life.
You can read more about both of these processes in just about any college Biochemistry textbook. I hope that answers your question!
-Daniel Peisach
Biochemistry graduate student, Brandeis University
Try the links in the MadSci Library for more information on Biochemistry.