Question

True or false?

True False  Phenylalanine's side chain is more polar than tryptophan's or tyrosine's side chains.
True False  Almost all peptide bonds in proteins are in the trans configuration.
True False  In folded globular proteins, the side chains of hydrophobic amino acids are mostly buried in the interior of the protein.
True False  The peptides I-A-G-Y-L-S and S-L-Y-G-A-I are different molecules with different properties.
True False  Poly lysine will tend to form an alpha helix in solution at pH 6.8.
True False  Amyloidoses such as Huntington's, Alzheimer's, and Parkinson's diseases are caused by conversion of normally folded protein monomers to fibrillar aggregates of beta-sheet structures.

Answer 1

1). Phenylalanine's side chain is more polar than tryptophan's or tyrosine's side chains.

Ans: FALSE

As shown in the above diagram presence of ‘NH’ in tryptophan and ‘OH’ in tyrosine makes these two more polar than phenylalanine.

2). Almost all peptide bonds in proteins are in the trans configuration.

Ans: TRUE

The peptide bond in protein has some double bond character due to resonance. In this rigid peptide bond situation only the trans configuration leads to minimal steric hindrance and more stability.

3). In folded globular proteins, the side chains of hydrophobic amino acids are mostly buried in the interior of the protein.

Ans: TRUE

Globular proteins are mostly water soluble.

In its folded structure, hydrophobic(apolar) amino acids are buried in the interior whereas hydrophilic (polar) amino acids are projected outwards, allowing dipole-dipole interactions with the solvent(water), which explains its solubility.

4).The peptides I-A-G-Y-L-S and S-L-Y-G-A-I are different molecules with different properties.

Ans: TRUE

Though amino acids are same, the way they are arranged (sequence) is different making them different molecules with different properties. The case is just like structural isomers where the composition will be same but the structure and properties are different

5).Poly lysine will tend to form an alpha helix in solution at pH 6.8.

Ans: FALSE

Poly(L-lysine) exists in a random-coil formation at a low pH, alpha-helix at a pH above 10.6, and transforms into beta-sheet when the alpha-helix polylysine is heated.

6). Amyloidoses such as Huntington's, Alzheimer's, and Parkinson's diseases are caused by conversion of normally folded protein monomers to fibrillar aggregates of beta-sheet structures.

Ans: TRUE