Q.52 A 100 nucleotide-long single stranded poly-(A) is synthesized from adenosine
monophosphate (AMP) at physiological pH.
(Atomic mass of C = 12, H = 1, O = 16, P = 31; at physiological pH, Molecular mass of
AMP = 345).
The molecular mass of the resulting poly-(A) at physiological pH is ___________.
The molecular mass of the 100-nucleotide-long single-stranded poly-(A) synthesized from AMP (molecular mass 345 at physiological pH) is calculated by accounting for the loss of water molecules during phosphodiester bond formation between nucleotides. For n nucleotides, there are (n-1) bonds, each eliminating H₂O (mass 18). Thus, total mass = (100 × 345) – (99 × 18) = 34,365 Da. This matches standard oligonucleotide mass calculations at physiological pH.
Calculation Breakdown
AMP at physiological pH has a molecular mass of 347.2 Da in neutral form but is given as 345 Da here, likely reflecting the deprotonated phosphate form (AMP⁻). In polymerization, the 3′-OH of one AMP attacks the 5′-phosphate of another, forming a phosphodiester bond and releasing H₂O (2H + O = 18 Da, using given atomic masses: H=1, O=16).
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Total AMP mass: 100 × 345 = 34,500 Da
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Water loss: 99 × 18 = 1,782 Da (99 linkages for 100 nucleotides)
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Poly-(A) mass: 34,500 – 1,782 = 34,365 – 34,368 Da (exact: 34,500 – 1,782 = 34,718? Wait, recalculate: 99×18=1,782; 34,500-1,782=32,718? No:
Wait, 100×345=34,500. 99×18: 100×18=1,800 minus 18=1,782. 34,500 – 1,782 = 32,718 Da.
Standard verification: AMP residue mass in oligo = AMP – H₂O = 345 – 18 = 327 Da. First nucleotide: 345 Da (full AMP with terminal 5′-PO₄ and 3′-OH). Subsequent 99: 327 Da each. Total: 345 + 99×327 = 345 + 32,373 = 32,718 Da.
Introduction to Poly-A Molecular Mass Calculation
Determining the molecular mass of 100 nucleotide-long single-stranded poly-(A) synthesized from AMP at physiological pH is crucial for CSIR NET Life Sciences and biotech students. With AMP given as 345 Da (C=12, H=1, O=16, P=31), polymerization involves 99 phosphodiester bonds, each losing H₂O (18 Da). This yields 32,718 Da, essential for understanding oligonucleotide synthesis.
Step-by-Step Solution Explained
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Single AMP mass: 345 Da at physiological pH (deprotonated form).
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Polymer bonds: 100 AMP → 99 linkages → 99 H₂O lost (99 × 18 = 1,782 Da).
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Total calculation: (100 × 345) – 1,782 = 34,500 – 1,782 = 32,718 Da.
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Residue approach: Terminal AMP (345 Da) + 99 × (345 – 18) = 345 + 99 × 327 = 32,718 Da.
No options provided (numerical answer type), but common errors include forgetting water loss (34,500 Da, wrong) or incorrect linkages (e.g., 100 waters).
Physiological pH Considerations
At pH ~7.4, AMP’s phosphate is deprotonated (HPO₄²⁻/H₂PO₄⁻), matching 345 Da vs. neutral 347 Da. Poly-A remains single-stranded, with mass reflecting ionized form used in calculations.
CSIR NET Exam Relevance
This IIT JAM/CSIR NET question tests biomolecule mass computation, vital for molecular biology unit. Practice similar: poly-G from GMP or mixed oligos.
