Question

a. What is the difference between DNA and chromatin? Name one type of molecule that distinguishes these two forms of genetic information.

b. What is a nucleosome, and what role does it play in cells?
c. Why does DNA need to be compacted inside cells?
d. Are any proteins used to keep DNA compacted other than proteins already present in chromatin?

Answer 1

a). DNA is the simplest form of genetic material consisting of nitrogenous bases (A,G,C,T), deoxyribose sugar and phosphate. On the other hand chromatin is DNA associated with proteins. These proteins are called histones and help in the packaging of DNA so that it could be accomodated inside the nucleus.

b). When the DNA is packaged around the histone proetins (H2A, H2B, H3,H4), it forms a structure called nuleosome which can be depicted by the "beads on string model" in which the beads represent the repeating nucleosome units. It forms a 30nm fibre and its main role is to help in the packaging of DNA so that it can be condensed in a small nucleus.

c). The compaction of DNA inside nucleus serves many functions such as

1).DNA is condensed within nucleus

2). DNA is also protected from demage

3). It regulates the expression of genes by modifying the structure of chromatin between heterochromatin and euchromatin.

d). Yes , various other proteins are also involved in keeping the DNA compact like non histone acidic proteins (topo 2), condensins and cohesins.