ch369_ch 15-nitrogen

ch369_ch 15-nitrogen - Nitrogen metabolism(Chapter 15 in...

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Unformatted text preview: Nitrogen metabolism (Chapter 15 in text) Roots & root nodules. Many of the molecules in living things are rich in nitrogen. For example, nucleic acids contain bases A, C, G, T, U. Proteins contain amino acids. Living things clearly require lots of nitrogen. Interestingly, we are surrounded by nitrogen (air is about 78% N 2 ). But biologically useful nitrogen is relatively scarce. The problem with air is that N 2 is not very chemically reactive. It is possible for organisms to be starved for nitrogen while being surrounded by N 2 in the air! A problem is: How to get biologically useful nitrogen from the N 2 in air ? Why is N 2 in the air so useless? The N-N triple bond is difFcult to break, so N 2 is chemically inert. Biologically more useful nitrogen includes ammonia (NH 3 ), amino acids, nucleotides, nitrates (NO 3- ), nitrites (NO 2- ). The N 2 + 3 H 2 ==> 2 NH 3 reaction is thermodynamically favorable, but has high activation energy. Ammonia can be obtained from N 2 by the “Haber process”, which is industrially important. N 2 + 3 H 2 ==> 2 NH 3 In industry, this reaction is carried out at high temperature and pressure. Cells can NOT make NH 3 this way. Cells need is a catalyst to lower the activation energy and get the reaction going at a reasonable rate! The ultimate source of nearly all biological nitrogen is the air. We (humans) must get nitrogen in our diet, mostly by eating proteins. Some bacteria and archaea have an enzyme catalyst for converting N 2 in air to biologically useful nitrogen. This process is called “ nitrogen Fxation ”. N 2 in air ==============> biologically more useful nitrogen Biologically more useful nitrogen = more reactive nitrogen. Ammonia NH 4 + Nitrate NO 3- Nitrite NO 2- Who can fx nitrogen From air? Not us! Some bacteria can fx nitrogen From air (such as those that colonize root nodules in plants) & some archaea can fx nitrogen From air. Bacteria that can fx nitrogen are called “ diazotrophs ”. Plants can’t fx nitrogen (but many plants have symbiotic relationships with diazotrophs). Some animals also have symbiotic relationships with diazotrophs (termites, For example, this helps them exist on a low-nitrogen diet). How do diazotrophs fx nitrogen ? They have an enzyme called “ nitrogenase ” and a protein that can Function as a strong reducing agent (“Ferridoxin”)....
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This note was uploaded on 08/26/2010 for the course CH 369 taught by Professor Kbrowning during the Spring '07 term at University of Texas.

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ch369_ch 15-nitrogen - Nitrogen metabolism(Chapter 15 in...

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