Question

Which is not the true statement?
A. $ \alpha - $ carbon of cc- amino acid asymmetric.
B. All proteins are found in $ L - $ form.
C. Human body can synthesize all proteins they need.
D. At $ pH = 7 $ both amino and carboxyl groups exist in ionised form.

Answer 1

Hint: Amino Acids are chemical molecules that combine to produce proteins and are hence known as the building blocks of proteins. Basic amino groups ( $ - N{H_2} $ ) and carboxyl groups are found in amino acids ( $ - COOH $ ). Proteins are made up of amino acid components.

Complete answer:
Amino acids are chemical molecules possessing amine ( $ - N{H_2} $ ) and carboxyl ( $ - COOH $ ) functional groups, as well as a side chain ( $ R - $ group) that is unique to each amino acid. cc-amino acid's $ \alpha - $ carbon is asymmetric. Hence, option A. is correct.
Proteins exist in both $ D $ and $ L - $ form. Hence, option B. is an incorrect statement.
The human body produces all of its own proteins. The digestive system breaks down the proteins you eat into individual amino acids, which then enter the bloodstream through the small intestine. They are then delivered into cells via the bloodstream, where they are reassembled into new proteins using ribosomes. Because proteins are specialised molecules that must be produced in a specific manner in order to accomplish their function, this is required. Hence, option C. is correct
Both amino and carboxyl groups are ionised at $ pH = 7 $ , resulting in the Zwitterion. Hence, option D. is correct.
Hence, option B. All proteins are found in $ L - $ form is not a true statement.

Note:
Almost all naturally occurring proteins, including milk protein, have all of their amino acids in the $ L $ confirmation. The $ D - $ form of amino acids is only seen in a few isolated occurrences, most notably in short peptide chains found in bacterial cell walls and in several peptide antibiotics.