Question

The main components of the ribosome are
A. Protein and RNA
B. Sucrose
C. Starch
D. Glycogen

Answer 1

Hint: A ribosome is defined as the granular structure that was first observed under the electron microscope as dense particles by George Palade (1953). They are made up of two important macromolecules and are not surrounded by any membrane.

Complete answer:
a) Location: Ribosomes are mainly located in all kinds of cells, i.e. prokaryotic as well as eukaryotic cells. In prokaryotic cells, they are present freely in the cytoplasm, whereas in a eukaryotic cell, they are present freely in the cytoplasmic matrix and are attached to the outer surface of the rough endoplasmic reticulum and the nuclear envelope. Ribosomes are also located in the matrix of the mitochondria and the stroma of plastids in eukaryotic cells.
b) Types of the ribosomes: The eukaryotic ribosome is the 80S kind and that of the prokaryotic ribosome is 70S. Here, the sedimentation coefficient is used and is indirectly a measure of the density and size. Both 70S and 80S are made up of two subunits.
c) Chemical composition: A ribosome is composed of highly folded rRNA molecules and many attached proteins and magnesium ions. They are composed of proteins and RNA (rRNA). Usually, three to four rRNA molecules and about forty to eighty different ribosomal proteins are observed in the ribosomes.
d) Functions of ribosomes: Ribosomes play a role in providing space for the synthesis of proteins in the cell. Hence, they are termed as protein factories of the cell. Ribosome furnishes enzymes and factors required for the formation of polypeptides. It also gives sites for the attachment of tRNA and mRNA which participate in protein synthesis and help to form the site for the synthesis of the polypeptide.
Hence, the correct answer is option A.

Note: Escherichia coli cell may constitute 20,000 to 30,000 ribosomes and a eukaryotic cell may contain up to half a million ribosomes. It plays an important role in translation, i.e. the mRNA comes and binds to the smaller ribosomal subunit.