2-Amino adenosine, phosphorylation

The phosphorylation of adenosine to adenosine-5 -phosphate was demonstrated some time ago in crude yeast extracts. The extracts did not act on guanosine, and no yeast adenylic acid was formed. More recently it has been found that the synthesis involves transfer of phosphate from ATP to adenosine, and the term adenosine phosphoki-nasc has been applied to the enzyme. The activity occurs in yeast maceration juice and in kidney and liver extracts of the rat and rabbit. The enzyme is quite specific, for a partially purified brewers yeast preparation catalyzes the phosphorylation of only two nucleosides out of seventeen which have been tested. The two nucleosides are adenosine itself and 2,6-diaminopurine riboside (2-amino adenosine). The reactions are ... 

From this observation of the inhibition by adenosine, and other observations, Newell and Tucker suspected the existence of a common synthetic pathway for adenosine and thiamine, and proved (with the help of a collection of mutants) that the bifurcation occurred after the 5-amino- l-(P-D-ribofura-nosyl)imidazole 5 -phosphate (46) step (Scheme 23). Finally, they found that 5-amino-l-(0-D-ribofuranosyl)imidazole (47), labeled with l4C in the imidazole ring, was incorporated into pyramine without significant loss of molar radioactivity by a mutant that is able to use this nucleoside (presumably after phosphorylation).53,54... 

The interesting observation has been made that 3 -amino-3 -deoxy-adenosine as a suspension in phosphoryl chloride-triethyl phosphate at 4° is converted into the 5 -chloro-5 -deoxy derivative in 80% yield, but that predissolution of the nucleoside in triethyl phosphate, followed by treatment with phosphoryl chloride at 0°, yields the 5 -phosphate in 62% yield.382... 

The 5 -terminal residue usually is a guanine nucleotide it is phosphorylated at the 5 -OH. The terminus at the 3 end has the same sequence of three nucleotides in all tRN A s, namely, CCA. The 3 -OH of the adenosine in this grouping is the point of attachment of the tRNA to its specific amino acid ... 

These are the energy producers within the cell. They generate energy in the form of Adenosine Tri-Phosphate (ATP). Generally, the more energy a cell needs, the more mitochondria it contains. Site for Kreb s Citric Acid Cycle Electron transport system and Oxidative Phosphorylation Fatty acid oxidation Amino acid catabolism Interconversion of carbon skeletons. 

Robert Holley first determined the base sequence of a tRNA molecule in 1965, as the culmination ul 7 years of effort, Indeed, his study of yeast alanyl-tRNA provided the first complete sequence of any nucleic acid. This adapter molecule is a single chain of 76 ribonucleotides (Figure 30.2). The 5 terminus is phosphorylated (pCi), whereas the 3 terminus has a free hydroxyl group. T he amino acid-attachment site is the 3 -hydroxyl group of the adenosine residue at the 3 terminus of the molecule. The sequence 5 - IGC-3 in the middle of the molecule is the anticodon, where I is the purine base inosine. It is complementary to 5 -GCC-3, one of the codons for alanine. 

The answer is e. (Murray, pp 452—467. Sciivei pp 3—45. Sack, pp 1—40. Wilson, pp 101-120.) For transfer RNAs, the 5 end is often guanosine and is always phosphorylated, while the 3 end is CCA. Although transfer (t) RNA molecules have many features in common, the primary feature that sets them apart is their specificity for different amino acids and the corresponding specific differences of their anticodons. Each tRNA is an L-shaped single chain composed of up to 93 ribonucleotides. Each contains up to 15 methylated bases, and about half of the nucleotides are base-paired into double helices. Activated amino acids attach to the terminal 3 -hydroxyl group of the adenosine. 

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