Question

Which of the following correctly describes chromatin?
(A) the complex of DNA and protein from which chromosomes are composed
(B) the total genetic content of a cell
(C) the proteins that give structural support
(D) unpacked DNA

Answer 1

Hint Human DNA is 2.2 metres long, so it has to be compactly packed so as to fit in the nucleus. Chromatin is made up of DNA and histone proteins, these later condense more during cell division and form chromosomes. Chromatin has beads on a string-like appearance where the string is represented by DNA strands and beads are represented by histone proteins.
Step by step solution
DNA present in our nucleus does not lie freely or as free linear strands, it is highly coiled and condensed and wrapped around nuclear proteins so that it can fit inside the nucleus.
Chromatin exists in two forms that are heterochromatin and euchromatin.
Heterochromatin is tightly bound or highly packed chromatin, it is densely stained and also is transcriptionally less active or inactive.
Euchromatin is loosely packed chromatin, it is lightly stained and is transcriptionally active as well.
Chromatin is packed in such a way in the diploid cells that it can be divided into 46 chromosomes. When DNA starts condensation, initially it binds with histone proteins (basic proteins as DNA is acidic in nature) the first structure formed when DNA combines with histones and forms a long chain is known as chromatin, it appears as beads on a string, on further condensation it forms nucleosome and then solenoid and then finally chromosomes.
The total content of DNA in a haploid cell is known as the genome.
Chromatin makes it possible for a lot of processes to occur which include DNA replication, transcription, DNA repair, genetic recombination, and cell division.
so, option (A) is correct
Note: All the structures that are nucleosome, solenoid and chromosomes are all made up of DNA and histones or we can also say that all are made by condensation of chromatin at various levels or various degrees.