BBMB 405 1st Edition Lecture 19 Outline of Last Lecture XVI. Chapter 24: The biosynthesis of Amino AcidsD. Amino acids are precursors of many biomoleculesXVII. Chapter 25: Nucleotide BiosynthesisA. Nucleotides can be synthesized by de novo or salvage pathwaysB. The pyrimidine ring is assembled de novo or recovered by salvage pathwaysOutline of Current Lecture XVII. Chapter 25: Nucleotide BiosynthesisB. The pyrimidine ring is assembled de novo or recovered by salvage pathwaysC. Purine bases can be synthesized de novo or recycled by salvage pathwaysD. Deoxyribonucleotides are synthesized by reduction of ribonucleotides through a radical mechanismE. Key steps in nucleotide biosynthesis are regulated by feedback inhibitionF. Disruption in nucleotide metabolism can cause pathological conditionsCurrent LectureXVII. Chapter 25: Nucleotide BiosynthesisB. The pyrimidine ring is assembled de novo or recovered by salvage pathways1. Orotate acquires a ribose ring from PRPP to form a pyrimidine nucleotide and is converted into uridylate (memorize reactions in this section)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.a.b. Orotic aciduria in humans: caused by defiecency of UMPS (orotate + PRPP  OMP + PPi, treated with dietary CMP and UMP, can lead to mental and physical retardation and anemia (can’t make pyrimidine nucleotides)c. 2. Nucleotide moni-, di- and triphosphates are interconvertiblea. UMP + ATP <-> UDP + ADPb. XDP + YTP <-> XTP + YDP3. CTP is formed by amination of UTPa. UMP  UDP  UTP  CTPb. Conversion of UMP to UDP and UDP to UTP requires ATPc. Conversion of UTP to CTP requires glutNH2 and ATP4. Salvage pathways recycle pyrimidine basesC. Purine bases can be synthesized de novo or recycled by salvage pathways (stated in class:do not repeat/memorize whole pathway)Know where each atom came from1. The purine ring system is assembled on ribose phosphatea.b. Rate limiting stepc. Note: glu is source of nitrogend. Controlled through mercaptopurine in cancer treatment: molecule is converted toa nucleotide that is an active inhibitor of DNA synthesis; excreted as thiocerate; allopurinol stops xanthine oxidase which converts mercaptopurine to thiocerate2. The purine ring is assembled by successive steps of activation by phosphorylation followed by displacement: make IMP requires 4 high energy phosphates so it is more efficient to use salvage, don’t memorize pathway3. AMP and GMP are formed from IMPa.b. Know pathway4. Enzymes of purine synthesis pathway associated with one another in vivoD. Deoxyribonucleotides are synthesized by reduction of ribonucleotides through a radical mechanism1. Mechanism: a tyrosyl radical is critical to action of ribonucleotide reductasea.b. NADPH is the source of electronsc. Control production of deoxyribose: hydroxyurea stops ribonucleotide reductase, considered toxic but essential for human health2. Stable radicals other than tyrosl radical are employed by other ribonucleotide reductases3. Thymidylate is formed by methylation of deoxyuridylatedUMP synthesis: UMP + ATP  ADP + UDP + NADPH  NADP+ + dUDP + ADP  dUMP + ATP4. Dihydrofolate reductase catalyzes regeneration of tetrahydrofolate, a one-carbon carriera.b. Tetrahydrofolate is regenerated with NADPHc. Extremely important for DNA synthesis5. Several valuable anticancer drugsa.b. Fluorouracil: consume to treat cancer, not actual inhibitor but converted to active form Fluorodeoxyuridylate which inhibits thymyldilate (suicide inhibitor)c. Fluorouracil is absorbed more efficiently by cancer cells than non cancer cellsd. FU + PRPP via salvage  fUMP + ATP  ADP + fUDP + NAPDH  NADP+ + fdUDP + ADP  ATP + fdUMP (inhibitor of thymidylate synthetase)   fdUTPe. Fluorodeoxyuridylate is suicide inhibitor: binds to enzyme and destroys so cell hasto make new – slow down or stop replicationf. Aminopterin or methotrexate inhibit dihydrofolate conversion to tetrahydrofolateg. Trimethoprim: used in urinary tract infection to slow down production of DNA in bacteria, used at lower but effective doses and has minimal effects on animal cellsE. Key steps in nucleotide biosynthesis are regulated by feedback inhibition (don’t memorize, but know general concept)1. Pyrimidine biosynthesis is regulated by asparatate transcarbamoylase2. The synthesis of purine nucleotides is controlled by feedback inhibition at several sites: AMP/GMP inhibit own synthesis, control cell division through energy supply (feedback inhibition)3. The synthesis of deoxyribonucleotides is controlled by regulation of ribonucleotide reductaseF. Disruption in nucleotide metabolism can cause pathological conditions1. The loss of adenosine deaminase activity results in severe combined immunodeficiencya.b. SCID: deciency of adenosine deaminase in T cells, inhibitor of ribonucleotide reductase – slow DNA synthesis; low [T cell] results in poor immune system response results in reoccurring infections result in early death/bubble boy disease, gene therapy may be cure2. Gout is induced by high serum levels of urate: Handout 2/273. Lesch-Nyhan syndrome is dramatic consequence of mutations in salvage pathway enzyme: decrease in salvage pathway activity, symptom is self mutilation, increase [urate] and incidence of kidney stones, xanthine oxidase (XO)4. Folic acid deficiency promotes birth defects such as spina