BIOC2600 1.7

• Amino acid metabolism I: Biosynthesis Dr Masayo Kotaka School of Biomedical Sciences [e-mail] LKS Faculty of Medicine
• Learning Objectives After today’s lesson, you should be able to: Describe how ammonium ions are assimilated into amino acids.
• Categorise different amino acids by their carbohydrate origins.
• Nitrogen Cycle and Nitrogen fixation Atmospheric N2 needs to be converted into ammonia (NH3) before it can be used by biological systems in a process called nitrogen fixation.
• Higher organisms are NOT capable of fixing nitrogen.
• Nitrogen fixation is performed by some bacteria and archea.
• In humans, the NH4+ group from glutamine is transferred to aspartate.
• The precursor of serine is 3-phosphoglycerate.
• Those obtained in human diet are primarily derived from plants.
• Amino acids are also precursors of other small molecules with important and diverse biological roles.
• Amino acids are building blocks for proteins and polypeptides.
• Glycine does not have any side chains and is synthesised from serine via losing the side chain methylene group.
• Serine acts as a precursor for glycine and cysteine.
• Pathways for synthesis of essential amino acids are more complex compared to those for nonessential amino acids.
• Cysteine is synthesised from serine and homocysteine, a non-proteinogenic amino acid.
• Glutamate is the precursor for proline and arginine.
• Essential amino acids are synthesized by plants and microorganisms.
• Aspartate and Alanine can be converted into amino acids in one step by the addition of the amino group from glutamate using amino transferases.
• These amino acids must be obtained from diet and are called essential amino acids.
• Essential and non-essential amino acids are different in that most microbes can synthesize the entire set of amino acids, humans cannot make 9 of them.
• Like synthesis of glutamine, addition of a 2nd NH4+ group would yield asparagine from aspartate.
• The remaining amino acids are called nonessential amino acids.
• Assimilation of ammonium ion into amino acids requires the entry of ammonium ion (NH4+) into amino acids.
• A second NH4+ is incorporated into glutamate to form glutamine via the reaction NH4+ + glutamate + ATP → glutamine + ADP + Pi.
• The first NH4+ is incorporated into glutamate via the reaction NH4+ + α-ketoglutarate + NADPH + H+ → glutamate + NADP+ + H2O.
• Assimilation of nitrogen requires the entry of ammonium ion (NH4+) into amino acids.
• Assimilation of nitrogen requires the entry of ammonium ion (NH4+) into amino acids via the synthesis of 2 amino acids, glutamate and glutamine.
• Symbiotic Rhizobium bacteria form root nodules in which they fix nitrogen at the roots of leguminous plants to supply both the bacteria and the plants.