Statement I ; All proteins are poly peptides with high molecular weight

Statement II ; All poly peptides are proteins with low molecular weight

Peptide bond formation;

$-\mathrm{COOH}+{\mathrm{H}}_2\mathrm{N}-\stackrel{-{\mathrm{H}}_2\mathrm{O}}{\to }-\mathrm{CO}-\mathrm{NH}-\left(\mathrm{peptide} \mathrm{linkage}\right);$

Condensation of $\mathrm{\alpha }-$amino acids involves loss of water molecules ; 

-OH from $-\mathrm{COOH}$ and -H from $-{\mathrm{NH}}_2$ lose as water;

Number of peptide linkages= n-1 (n=number of amino acid residues)

Thus condensation of

a) two amino acids(one peptide bond) gives a dipeptide

b) three amino acids(two peptide bonds) gives a tripeptide

c) 2-10 amino acids gives oligo peptides

d) >10 amino acids gives a poly peptides

e) If the molecular weight of a poly peptide is equal to greater than 10,000u containing a minimum  of 100 amino acid residues, it is a protein;

f) Thus all proteins are poly peptides but the reverse is not always true