Nucleotides are building blocks of nucleic acids. Each nucleotide is a composite molecule formed by

Thirty percent of the bases in a sample of $DNA$ extracted from eukaryotic cells is adenine. What percentage of cytosine is present in this $DNA$ ?

If the distance between two consecutive base pairs is $0.34\, nm$ and the total number of base pairs of a $DNA$ double helix in a typical mammalian cell is $6.6 \times 10^{9}$ $bp,$ then the length of the $DNA$ is approximately 

Read the following statements and choose the set of correct statements:

$(a)$ Euchromatin is loosely packed chromatin

$(b)$ Heterochromatin is transcriptionally active

$(c)$ Histone octomer is wrapped by negatively charged DNA in nucleosome

$(d)$ Histones are rich in lysine and arginine

$(e)$ A typical nucleosome contains $400\,bp$ of DNA helix

Choose the correct answer from the options given below:

Distinguish between heterochromatin and euchromatin. Which of the two is transcription-ally active ?

Give the historical background of $DNA.$