Question

A ribosome is composed of:
(a) Single unit
(b) Two subunit
(c) Three subunit
(d) Four subunit

Answer 1

Hint: Ribosomes are cell organelles present in the cytoplasm. They are composed of rRNA and proteins and are membraneless. They comprise multiple subunits which come together to form a single ribosome.

Complete answer:
The ribosomes are composed of two subunits. One ribosomal subunit is large and has a dome-like shape, while the other ribosomal subunit is smaller in size and occurs above the larger subunit and forms a cap- like structure.
The two ribosomal subunits remain united with each other due to the specific concentration of magnesium ion. When the concentration of magnesium ions reduces below a critical level both ribosomal subunits get separated.
Ribosomes are of two types, the 70S and 80S, where S represents the coefficient which indirectly measures the density and size of ribosomes.
- Functions:
Ribosomes are sites of protein synthesis. The free ribosomes synthesize non- secretory proteins, while ER bound ribosomes synthesize secretary proteins. Free ribosomes synthesize structural and enzymatic proteins for use inside the cell. The attached ribosomes synthesize proteins for transport. Thus, these organelles are also known as protein factories. Newly synthesized proteins are processed with the help of chaperon proteins.
Additional Information:
- 70S ribosomes are made up of ribonucleoproteins in the ratio of 60:40 (RNA: Protein)
- 70S ribosomes consist of 30S smaller subunit and 50S larger subunit
- 80S ribosomes are made up of ribonucleoproteins in the ratio of 40:60 (RNA: Protein) .
- 80S ribosomes consist of 40S smaller subunits and 50S larger subunits.

So, the answer is, “Two subunits.”

Note: The ribosomes of prokaryotes are the 70S and that of eukaryotes is 80S. In mitochondria chloroplasts, ribosomes are the 70S. The reason behind this is that they are believed to have originated from prokaryotes that were engulfed by certain eukaryotes and then developed a symbiotic relationship.