BIOLCHEM 415 1st Edition Lecture 26 Outline of Last Lecture I. Phospholipids, sphingolipids, and cholesterol are the three major classes of lipidsII. Cholesterol synthesis occurs mostly in the liverIII. HMG-CoA is highly regulatedOutline of Current Lecture IV. Amino acid degradation occurs when there are excess amino acids in the bodyV. The Urea Cycle is needed to convert toxic ammonium to a nontoxic ureaCurrent LectureAmino Acids- biosynthetic reactions- proteins/nitrogenous compounds- degradation- can’t be stored in the body- occurs in liver and muscle (energy)- 2 step process- remove amino group and recycle carbon skeletonNitrogen removal- α-amino group ammonium ions- through intermediate glutamate- aminotransferase = transaminase catalyze the reaction- amino acid + α-ketoacid α-ketoacid + second amino acid (glutamate)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- remaining α-ketoacids usually can enter other cycles- ex: oxaloacetate, pyruvate- funnels all α-amino groups into 1 intermediate (glutamate)Liberate ammonia from glutamate- oxidative amination- glutamate dehydrogenase- mitochondrial enzyme- good because the toxic ammonia is sequestered in one place (mitochondria)Serine and Threonine- direct deamination- catalyzed by dehydratases- serine aminoacrylate pyruvate- threonine α-ketobutyrate + NH4+- both have hydroxyl groups at β-carbon- what allows direct deaminationAmmonia toxicity- NH4+ urea and excreted - ureotelic = excess ammonia converted to urea and excreted- ammoniotelic = release nitrogen as NH4+ into their environment- uricotelic = nitrogen secreted as purine uric acidUrea Cycle- in humans it occurs in the liver- transport nitrogen to liver- alanine (muscle) or glutamine- Glucose-alanine cycle- muscle uses branched chain amino acids for degradation (Leu, Ile, Val)- glucose pyruvate alanine- NH4+ from branched amino acids alanine- alanine to blood stream to liver- alanine degraded normally and NH4+ enters the urea cycle- glutamine transport- first biochemical cycle described1 – synthesis of carbamoyl phosphate2 – carbamoyl phosphate enters cycle in reaction with ornithine- anhydride bond- produces citrulline- exits mitochondria into cytosol - both citrulline and ornithine are amino acids - they are not used for protein synthesis3 – aspartate contributes another amino group- produces argininosuccinate - occurs in cytoplasm4 – form arginine and fumarate- fumarate is the carbon skeleton of aspartate5 – urea- arginine ornithine + urea- this cycle produces enough arginine in adults but not in children- arginine is an essential amino acid for childrenUrea Cycle linked to TCA cycle- aspartate needed for the urea cycle- can be generated from fumarate by TCA cycle reactionsUrea cycle defects- argininosuccinase deficiency - can’t produce arginine and fumerate- treatment = adding arginine to the diet- argininosuccinate can be excretd from the bodyCarbon skeletons- metabolic intermediates (10-15% of metabolic energy)- 7 carbon skeleton intermediates- acetyl CoA, fatty acids, pyruvate, four TCA components- ketogenic (form fat not glucose) or gluconeogenic (used in net synthesis of glucose)- 14 gluconeogenic, 4 both, 2 ketogenic- pyruvate (ala, ser, cys, thr)(sort of Trp)- propional CoA (Met, Val, Ile)Degradation of aromatic amino acids- monooxygenases and dioxygenases- tryptophan- uses both mono and diPhenylketonuria- phenylalanine hydroxylase deficiency- impaired brain development and intellectual
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