Question

Which of the following structures is called a 'little nucleus'?
(A) Nucleolus
(B) Nucleoid
(C) Ribosome
(D) Lysosome

Answer 1

The structures from the above which are called 'little nucleus' is the region found within the cell nucleus that is concerned with producing and assembling the ribosomes of the cell.This structure is absent in many types of cells like muscle fibers, red blood cells of blood , yeast, sperm cell, and also in the case of prokaryotes.

Complete solution:
The nucleolus is known as the 'little nucleus' because it is the largest structure that is present in the nucleus. The nucleolus is defined as a region that is found within the cell nucleus that is concerned with producing and assembling the cell's ribosomes. Following assembly, the ribosomes are then transported to the cell cytoplasm where they serve as the sites for protein synthesis.
Within the nucleus, there is a very specific part called the nucleolus. This doesn't contain the chromosomes. What this contains is that the machinery necessary to assemble the cell's ribosomal RNAs. Ribosomal RNAs are then transported through the nuclear pores into the cytoplasm where they become a part of the ribosome, which is the protein machinery. These ribosomal RNAs guide the messenger RNAs through the ribosomes and help within the protein translation, but they themselves are RNA's that don't become proteins. They're known as non-coding RNAs that help the messenger RNAs to undergo the protein translation process. These types of RNAs, just like the other messenger RNAs, are made within the nucleus, but ribosomal RNAs are made within the nucleolus which may be a very specific part of the nucleus.

So, the correct answer is ‘Nucleolus’.

Note:
Nucleolus was first observed by the Fontana in the skin cell of an eel. The nucleolus is absent in the muscle fibers, RBC, yeast, sperm, and also in the case of prokaryotes.It is also considered as the brain of the nucleus. It was found to cover nearly 1/4 volume of the nucleus. Primarily, it takes part within the production of subunits that unites to make ribosomes.