Question

Choose the correct statement
A. All proteins are formed from 20 amino acids
B. Both ends of a protein are similar
C. All proteins are soluble
D. Proteins are formed by glycosidic bonds

Answer 1

Hint: DNA (or RNA) carries all genetic information. It is expressed in the form of proteins which are made up of a number of different types of amino acids. The sequence and combination of amino acids are determined by the information present in the mRNA.

Complete answer:
- All the proteins in a cell are made up of the same 20 amino acids by using different combinations and sequences. All of these 20 amino acids have the carboxyl, amino, and the R group attached to the same carbon. All of them are α amino acids.
- Amino acids bind to each other with the help of the amino and the carboxylic group. Therefore, the two ends of a protein cannot be similar. One end of the polypeptide chain is referred to as the N-terminal and has the amino group. The other end of the polypeptide in a protein has the carboxyl group and is thus referred to as the C-terminal.
- Proteins are composed of 20 different amino acids which are hydrophobic and hydrophilic in nature according to the R group present in it. Thus, the overall hydrophobicity and hydrophilicity of the protein depend on the amount and arrangement of hydrophobic and hydrophilic amino acids. This decides the solubility of the protein. Therefore, it cannot be said that all proteins are soluble.
- Proteins are bound to each other by a bond formed by the amino and the carboxyl group, often referred to as the peptide bond. Proteins do not have glycosidic bonds.
- Therefore, the correct answer is (A) All proteins are formed from 20 amino acids

Note: The amino acids are coded by the mRNA that contains a variety of codons made by the combination of just four nitrogenous bases, namely Adenine, Guanine, Cytosine, and Thymine (or Uracil). These four bases can form 64 different codons coding for these 20 amino acids.