Question

Assuming atomic mass number of \(C=12\), \(N=14\), \(O=16\), \(H=1\), the molecular mass (in Daltons) of a tripeptide made up of only glycine amino acids is _ _ _. (in integer)

Hint:

For peptide formation: \[ \text{Mass of peptide} = \text{Sum of amino acid masses} - 18\times(\text{number of peptide bonds}) \] because each peptide bond formation removes one water molecule.

Answer 1

Correct Answer: 189

Step 1: Glycine formula and mass.
Glycine is $C_2H_5NO_2$. Its mass is $2(12)+5(1)+14+2(16) = 24+5+14+32 = 75$ Da.

Step 2: Add three glycines.
Three free glycines weigh $3\times 75 = 225$ Da.

Step 3: Account for peptide bonds.
Joining three amino acids forms two peptide bonds, and each bond releases one water molecule.

Step 4: Subtract the water.
Two waters weigh $2\times 18 = 36$ Da, so the tripeptide weighs $225 - 36 = 189$ Da.

Step 5: Answer.
\[ \boxed{189\ \text{Da}} \]