8. The Autotrophic Way of Life Flashcards
Describe autotrophs.
An organism that uses in organic carbon, usually carbon dioxide, as a carbon source.
What are the pathways autotrophic bacteria used to perform assimilative carbon dioxide reduction?
The Calvin cycle, reverse TCA cycle, hydroxypropionate pathway, acetyl CoA pathway.
What are the two main autotrophs?
Lithotrophs and phototrophs. Lithotrophs use inorganic chemicals for energy source and electron source. Phototrophs use light as energy and inorganic chemical as electron source.
Describe the modes of catabolism of lithotrophs.
All ATP is made by oxidative phosphorylation. They exhibit only one form of catabolism which is respiration. Unlike the respiration of organic molecules by most heterotrophs, the respiration of inorganic chemicals does not involve NAD as an electron carrier. The same chemical that serves as an energy source for ATP synthesis also serves as the electron source for reducing NADP+ to NADPH. This reduction requires energy supplied by the transport are protons along the membrane.
Describe the diversity of lithotrophic catabolism.
For the most part, all of them use the same energy sources and TEAs by the same basic mechanisms. Two exceptions are the lithotrophic methanogens and anammox bacteria.
Describe lithotrophic methanogens.
Some obligately anaerobic archaea have evolved to oxidize hydrogen gas using carbon dioxide producing methane as a waste product. These organisms also use hydrogen gas as an electron source to reduce NADP+.
Describe anammox bacteria.
While most ammonium oxidizers use oxygen as a TEA, these bacteria react ammonium with nitrite, performing an aerobic ammonia oxidation. They posses an anammoxosome, the site of anammox (ammonia oxidation). In the lumen, ammonium and nitrite are enzymatically reacted to yield hydrazine using electrons from an electron transport chain in the membrane. Hydrazine then donate electrons to the same chain, yielding nitrogen gas.
Describe chlorophyll-based phototrophic catabolism for ATP synthesis.
It has not been described in archaea. Like oxidative phosphorylation, the mechanism of photophosphorylation involves an ETC. however, photophosphorylation does not involve the use of electron donors in the scepters. The electron donors and the acceptors are called photosystems. Energy provided in the form of light drives electrons from a reduced photosystem to an oxidized photosystem.
Compare cyclic versus non-cyclic photophosphorylation.
In noncyclic photophosphorylation, different photosystem types serve electron donor and acceptor roles. Electrons travel by a non-cyclic route from one type photo system to another type of photo system. In cyclic photophosphorylation. The same type of photo system serves as both a electron donor and acceptor.
Describe NADPH synthesis for chlorophyll-based phototrophic catabolism.
There are two types of phototrophy: oxygenic in and anoxygenic. If they use water as an electron source and produce oxygen as a waste product, it is oxygenic. Green sulphur bacteria make NADPH using electrons from photosystem one. Electrons are replenished through the role of the electron source. Purple bacteria and FAPs produce NADPH using electrons from photosystem two. Additional energy is channelled into the reaction by the transport of protons from the periplasm to the cytoplasm.
Describe the noncyclic phosphorylation and synthesis of NADPH in cyanobacteria.
Noncyclic photophosphorylation and synthesis of NADPH are connected. Noncyclic photophosphorylation depends on photosystem one existing in an oxidized state so it can accept electrons from reduced two. Water donates electrons to photosystem two to replenish it with electrons. Water becomes oxidized to oxygen.
Describe the carbon used in anabolism for autotrophs.
Phototrophs are photosynthetic. Light reactions refer to catabolism and dark reactions referred to anabolism. The dark reactions use the ATP and NADPH from the light reactions to synthesize organic molecules from carbon dioxide and water. With the troops are chemosynthetic. They rely on chemical nutrients to synthesize the ATP and NADPH required to reduce carbon.
What are mixotrophs?
Autotrophs capable of growing using light or an inorganic energy source and TE a combination to produce energy and organic molecules as carbon and electron sources.
Define PS 2 based photophosphorylation.
Aerobic, anoxygenic purple phototrophic bacteria make ATP by PS 2 based cyclic photophosphorylation.
Define Proteorhodopsin-based photophosphorylation.
Some prokaryotes have a mechanism for harvesting light energy that does not involve chlorophyll. This mechanism involves the membrane proteins called bacteriohodopsin in archaea and proteorhopsin in bacteria. Retinal gives these proteins the ability to use light energy to transport protons across the membrane.
