BBCCT-113
Metabolism of Amino Acids and Nucleotides (Theory)
About the course
Proteins in the body are constantly synthesized and degraded, partially draining and refilling the cellular amino acid pools. The metabolism of amino acids involve a wide range of synthetic and degradative reactions by which amino acids are gathered and broken down to recover metabolic energy. Since amino acids contain element nitrogen, their chemical transformation is unique as it is different from metabolism of carbohydrates and lipids. There is a dynamic pool of amino acids in the blood. Most of them are incorporated in proteins. Non-essential amino acids are synthesized in the body while essential amino acids are required in the diet. Tissues have continuous access to individual amino acids for the synthesis of proteins and essential amino acid derivatives, such as neurotransmitters. The amino acid pool also provides the liver with substrates for gluconeogenesis and ketogenesis. The free amino acid pool is derived from dietary amino acids and the proteolysis of body proteins.
The liver is the major site of amino acid metabolism in the body and the major site of urea synthesis. The liver is also the major site of amino acid degradation, and partially oxidizes most amino acids, converting the carbon skeleton to glucose, ketone bodies, or C02. In liver, the urea cycle converts ammonia and the amino groups from amino acids to urea (see “Nitrogen > Urea Cycle” in the top menu), which is non-toxic, water- soluble, and easily excreted in the urine.
All nitrogen-containing compounds of the body are synthesized from amino acids - cellular proteins, hormones (e.g., thyroxine, epinephrine, insulin), neurotransmitters, creatine phosphate, heme in hemoglobin and cytochromes, melanin, purine and pyrimidine bases.
Nucleic acid metabolism is the process by which nucleic acids (DNA and RNA) are synthesized and degraded. Nearly all the cells can synthesize nucleotides de novo and from degradation products of nucleic acids. Nucleotides are also components of some of the central cofactors of metabolism.
Expected Learning Outcomes
After studying this course, you should be able to:
explain the importance of amino acid and nucleotide metabolism;
describe the synthesis of non-essential amino acids and their catabolism;
enlist de novo and salvage biosynthetic pathways of purine and pyrimidine nucleotides ; and
describe regulation and degradation of purine and pyrimidine nucleotides.
Self Learning Material
Block-1.pdfIn the first block, (Block 1) an overview of amino acid metabolism is given in Unit-1. The fate of amino acids derived from proteins is given in the next unit (Unit 2). Sections on catabolism of amino acids as well as their classification based on the fate of carbon skeleton are discussed in Unit-3. Defects in amino acid metabolism will help the learner to understand the inborn errors of metabolism. These disorders are described in last unit of the first block i.e Unit-4.
Block-2.pdfThe second block, (Block 2) gives an overview of amino acid biosynthesis, precursor function of amino acids and porphyrin metabolism. Unit-5 deals specifically with the biosynthesis of non-essential amino acids as well as their regulation. The role of biologically active amino acids derivatives such as hormones and neurotransmitters are outlined in Unit-6. A schematic description of heme biosynthesis is given in Unit-7.
Block-3.pdfThe third block addresses biosynthesis of purine and pyrimidine nucleotides. Step wise description of key steps involved in the de novo synthesis of purine and pyrimidne nucleotides both by de novo and salvage pathways is given in Unit-8 and Unit-9 respectively. Learners can also understand regulation of nucleotide biosynthesis explained elaborately in these units. Unit-10 underlies importance of nucleotide containing coenzymes.
Block-4.pdfBlock-4 of the course highlights the degradation of purine and pyrimidine nucleotides along with disorders of nucleotide metabolism. Because nucleic acids are ubiquitous in cellular material, significant amounts are ingested in the diet. Nucleic acids are degraded in the digestive tract to nucleotides by various nucleases and phosphodiesterases (Unit-11). A diverse group of disorders of nucleotide metabolism are discussed in Unit-12. Learners can understand integration of amino acid metabolism in Unit-13 in which organ specific metabolic profile is covered subsequently.