Question

PULS 2. Figure 3.7 shows a portion of the proposed model of a chromatin fiber. Select two different colors for the coding circles and the corresponding structures on the figure. Then, respond to the two questions that follow. O DNA helix Nucleosome Figure 3.7 1. What is the chemical composition of a nucleosome? (Be specific.) 2. What is the function of the nucleosome components named above? Il wolnoonsists of interphase and a mitotic phase

Answer 1

QUESTION I: CHEMICAL COMPOSITION OF NUCLEOSOME-

Each nucleosome is consists of two parts - DNA and histone proteins. In each nucleosome, 1.67 turns of DNA is wrapped around eight histone proteins (known as histone octamer).

And each histone octamer is consist of H2A, H2B, H4, H3 (x2) histone proteins.

Where H2A-H2B forms heterodimers and H3-H4 forms heterotetramers. The H2A-H2B dimer bonds with H3-H4 tetramers due to interaction between H2B and H4 histone proteins. Hence, forming the core of the nucleosome.

Also , two adjacent nucleosomes are joined by linker DNA.

QUESTION 2: FUNCTION OF ABOVE MENTIONED COMPONENTS-

DNA - The main role of DNA is storage of information for long term in the cells. The most important function of the DNA is amino acid sequence encoding using genetic code.

Linker DNA - linker DNA joins two adjacent nucleosomes and also in association with h1 holds the histone core together.

Histone- Histones are main proteins of chromatin. Histone also helps in gene regulation by compacting DNA and regulating chromatin.