The cell membranes are mainly composed of

Which one of the following is an essential amino acid?

Assertion : At isoelectric point,the amino acid does not migrate under the influence of an electric field.
Reason : At isoelectric point,amino acid exists as a zwitterion.

Amino acids can be classified as $\alpha$,$\beta$,$\gamma$,$\delta$ and so on,depending upon the relative positions of the amino group with respect to the carboxyl group. Which type of amino acids form polypeptide chains in proteins?

Which statement correctly completes the statement?
Except for glycine,which is achiral,all the amino acids present in proteins ......

Which of the following is a condensation polymer?