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Understand the process of amino acid breakdown and learn about the synthesis of urea. Explore the different strategies used by animals and the regulation of the urea cycle. Suitable for medical laboratory professionals and clinical biochemistry students.
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AL-Ma’moon University CollegeMedical Laberatory techniques Department Clinical biochemistry / Second stage ASS.Lec. SuadTurky Ali (Lec – 1-)
Metabolism of amino acids: • A similar process is used to break down proteins it is first hydrolyzed into it's component amino acids. Free ammonia (HK3) exiting as the ammonium (NH4+) ion in blood, is toxic to life forms. A suitable method of excreting is must therefore exist. • Different strategies have evolved is different animals, depending on the animal's needs, unicellular organisms of course, simply release the ammonia into the environment similarly, bony fish can release the ammonia into the water where is quickly diluted. • In general , mammals convert the ammonia into urea, via the urea cycle.
Amino acid catabolism: • The catabolism of amino acids usually begins with removal of the amino group. • Amino groups can then be disposed of in urea synthesis. • The carbon skeletons that are produced from the amino acids in this process are then degraded to from seven metabolic products : • Acetyl – COA • Aceto - acetyl – COA • Pyruvate. • ά – ketoglutarate. • succinyl – COA. • Fumarate. • oxaloacetate.
Depending on the animals current metabolic requirements , these molecules are used in the synthesis of : fatty acids : that can be converted to either fatty acids or ketone bodies are referred to as ketogenic. • Amino acids : which are degraded to pyruvate or a citric acid cycle intermediate referred to as glycogenic these can subsequently. • Urea synthesis : • Urea is formed from ammonia CO2, and asratate in acyclic pathway referred to as the urea cycle. • Because, the urea cycle was discovered by Hans krebsandkurthenseleit, 1932. it is often referred to as the krebs urea cycle or the krebs – henseleit cycle- urea synthesized in especially large amount when the diet is high in protein, or when there is massive breakdown of protein for example during starvation.
The urea cycle : or (ornithine cycle) • The urea cycle is a cycle of biochemical reactions occurring in many animal that produces urea }(NH2)2 co{ from ammonia. • In mammals, the urea cycle takes place primarily in the liver and to a lesser extent in the kidney organisms that cannot easily and quickly remove ammonia usually have to convert it to some other substances, like urea pr uric acid , which are much less loxic. • Insufficiency , of the urea cycle occurs in some genetic disorders (in born errors of me diabolism).
And in liver failure. The result of liver failure is accumulation of of nitrogenous waste, mainly , ammonia , which leads to hepatic encephalopathy designed to convert NH4+ to urea , cycle consist of five reactions : two mitochondrial and three catabolic. • The cycle converts two amino groups one from NH4 and one from aspartate , and a carbon a tom from HCO3- , to the relatively nontoxic excretion product urea at the cost of four "high energy" phosphate bonds (3AT & hydrolyzed to ADP and one AMP). Ornithine is the carrier of these carbon and nitrogen atoms.
The reactions of the urea cycle: • ornithine • carbamoyl phosphate. • L-citrylline • Arginisuccinate. • Fumarate • L-argnine • Urea
The net reaction for the urea cycle is : • Co2+NH4+ +Aspartate +3 ATP+2H2O Urea +Fumarate + 2ADP + 2Pi +AMP + PPi + SH+ • Or: • 2NH3 + Co2 +3ATP + H2o Urea +2ADP + JPi + AMP • The Urea cycle is carefully regulated to prevent hyperammonmia. • Hyperammonmia : is a condition in which there is an excessive concentration of NH4+ in blood.
