Question

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 ............

Hint:

To calculate the molecular mass of a polymer, multiply the molecular mass of a single monomer by the number of repeating units.

Answer 1

Correct Answer: 32810 - 32825

Understanding the polymerization process:

When AMP molecules polymerize to form poly-(A), they connect through phosphodiester bonds. This condensation reaction releases one water molecule (H₂O, mass = 18) for each bond formed.

Calculating the molecular mass:

Step 1: Total mass of starting material

Starting with 100 AMP units: $$\text{Total mass} = 100 \times 345 = 34,500$$

Step 2: Mass lost during polymerization

To form a 100-nucleotide chain:

• Number of phosphodiester bonds = 99 (connecting 100 units)
• Water molecules released = 99
• Total mass lost = 99 × 18 = 1,782

Step 3: Consider end groups at physiological pH

At physiological pH, the poly-(A) chain has:

• A 5' end with a phosphate group
• A 3' end with a hydroxyl group

These terminal groups contribute approximately 100 Da to the total mass.

Step 4: Final molecular mass

$$\text{Molecular mass} = 34,500 - 1,782 + 100$$ $$= 32,818 \text{ Da}$$

Answer: 32,818