Question

Which of the following are functions of ribosomes?
(i) It helps in the manufacture of protein molecules.
(ii) It helps in manufacture of enzymes.
(iii) It helps in the manufacture of hormones.
(iv) It helps in the manufacture of starch molecules.

A. (i) and (ii)
B. (ii) and (iii)
C. (iii) and (iv)
D. (i) and (iv)

Answer 1

Ribosomes were first isolated by a biologist, Albert Claude. He called the ribosomes ‘microsomal particles’. It was George Palade who gave the name ribosomes. No membrane surrounds the ribosomes and it is found in both prokaryotic and eukaryotic cells. They are found in the cytoplasm of the cell or bound to the membrane of the endoplasmic reticulum. They are also found in some cell organelle such as mitochondria and plastids.

Complete answer:
-Ribosomes are composed of rRNA and proteins. Prokaryotes have $70$s ribosomes while eukaryotes have $80$s ribosomes. The rate at which the ribosome sediments are denoted by the symbol ‘s’, this is called the sedimentation coefficient.
-Ribosomes have two subunits, a large subunit and a small subunit. In the case of membrane-bound ER ribosomes, the larger subunit is the one bound to the ER membrane. A protein called ribophorin helps with the attachment of the larger subunit to the ER membrane. The smaller subunit remains free and it binds to the larger subunit only during protein synthesis.
-Ribosomes synthesize proteins. The ribosomal subunits bind together and latch on to the mRNA. The smaller subunit has the mRNA binding site. The larger subunit has three sites where specific proteins perform their assigned work. At these sites, the codons on the mRNA are read. Each codon represents a specific amino acid. A chain of amino acids is formed as the mRNA gets translated. Amino acids make up protein.
-Enzymes are proteins; therefore, ribosomes do make enzymes.
-Hormones are molecules secreted by glands (endocrine glands). They influence or regulate the functioning of other organs or tissues in the body. They can be proteins, amino acids, or even steroids. -Since hormones also include steroids, options (B) and (C) are incorrect.
-Starch is a carbohydrate stored by plants. Hence, options (C) and (D) are also incorrect.

Hence, the correct answer is option (A).

Note: Ribosomal subunits need to assemble or bind together to begin protein synthesis. This assembly requires the presence of magnesium ions. The concentration of magnesium ion should be $0.001$M. If the concentration of the ion is less than that the ribosomal subunits dissociate. If the concentration of magnesium ions is more than $0.001$M dimers of the ribosomes are formed.