1. What is Molecular Weight?

Molecular weight (MW) is the sum of the atomic weights of all atoms in a molecule. For DNA and proteins, it's calculated by summing the weights of individual nucleotides or amino acids, then subtracting water molecules lost during polymerization.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( MW_{\text{nuc or aa}} \) — Molecular weight of each nucleotide or amino acid
• \( n \) — Number of residues in the sequence
• 18.0 — Molecular weight of water (lost during polymerization)

3. Importance of Molecular Weight

Details: Molecular weight is crucial for experimental design, buffer preparation, electrophoresis, mass spectrometry, and determining molar concentrations.

4. Using the Calculator

Tips: Enter either DNA (A,T,C,G) or protein (20 standard amino acids) sequence. The calculator automatically detects invalid characters.

5. Frequently Asked Questions (FAQ)

Q1: Does this include terminal modifications?
A: No, this calculates the unmodified sequence. Add modifications separately.

Q2: How accurate is this calculation?
A: It's theoretical. Actual MW may vary slightly due to isotopic distribution.

Q3: Does it work for modified nucleotides/amino acids?
A: No, only standard residues are included in the calculation.

Q4: What about double-stranded DNA?
A: This calculates single-stranded MW. For dsDNA, multiply by 2 and subtract appropriate counterions.

Q5: Why subtract water molecules?
A: Water is lost during polymerization (phosphodiester bonds in DNA, peptide bonds in proteins).