Question

A sulphur-containing amino acid is
A. Serine
B. Asparagines
C. Methionine
D. Proline

Answer 1

Hint: Amino acids are the building blocks of the proteins. There are 20 amino acids that are normal components of cell proteins. They are specified in the genetic code. An amino acid not specified by the genetic code called a rare amino acid.

Complete answer: Amino acids are composed of carbon, hydrogen, oxygen and nitrogen. Some amino acids have sulphur in their structure as well. For example, methionine and cysteine. Methionine is a unique amino acid. It can produce other sulfur-containing molecules in the body. It is also involved in starting protein production in body cells. It can also be converted into S-adenosyl methionine which plays an important role in post-transcriptional modification of DNA. Thus, amino acids differ from carbohydrates and fats in having nitrogen and sometimes sulphur. Amino acids are of three types based on their structure:
1. Sulphur containing amino acids: e.g. Cysteine, methionine.
2. Alcoholic amino acids: These amino acids have alcoholic or hydroxyl groups, e.g. serine, threonine.
3. Heterocyclic amino acids: These amino acids have nitrogen in the ring structure. Eg. Histidine, proline.
So, the correct answer is option C.

Additional information:Functions of amino acids:
a. Formation of proteins: the principal function of amino acids is to form proteins by polymerization involving peptide linkages.
b. Formation of glucose: many amino acids change into glucose by losing amino groups (gluconeogenesis).
c. Formation of amines: amino acids also form amines by losing the carboxyl group.
d. Nitrogen storage: the derivatives of the amino acids called amides serve as storage of nitrogen.
e. Biosynthetic pathways: the amino acids ornithine and citrulline play a role in the urea cycle in the liver cells.

Note: Serine and asparagine are non-polar amino acids i.e. they are soluble in water. Proline is polar uncharged amino acids. Amino acids are colourless, crystalline, solid compounds. They are generally soluble in water but insoluble in organic solvents. They are amphoteric, having both basic and acidic properties.