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: Write the molecular formula of glycine.
Glycine is the simplest amino acid and its molecular formula is
\[ C_2H_5NO_2 \]

Step 2: Calculate the molecular mass of one glycine molecule.
Using the given atomic masses:
\[ C=12,\quad H=1,\quad N=14,\quad O=16 \] Mass of glycine:
\[ =2(12)+5(1)+1(14)+2(16) \] \[ =24+5+14+32 \] \[ =75 \] Thus, molecular mass of glycine is
\[ 75\ \text{Da} \]

Step 3: Find the mass of three glycine molecules.
A tripeptide contains three glycine units.
\[ 3\times 75=225 \] So, total mass before peptide bond formation is
\[ 225\ \text{Da} \]

Step 4: Understand peptide bond formation.
When amino acids join to form peptide bonds, one water molecule
\[ (H_2O) \] is removed for each peptide bond formed.

Step 5: Determine number of peptide bonds.
A tripeptide formed from three amino acids contains
\[ 2 \] peptide bonds.
Hence, two water molecules are lost.

Step 6: Calculate mass loss due to water removal.
Mass of one water molecule:
\[ H_2O=2(1)+16=18 \] Mass of two water molecules:
\[ 2\times18=36 \]
Now subtract from total mass:
\[ 225-36=189 \]

Step 7: Final conclusion.
Therefore, the molecular mass of the tripeptide is
\[ \boxed{189} \]