Chapter 19, Problem 1TYK

What is chromatin?

a. the histone-containing protein core of the nucleosome

b. the 30-nm fiber

c. the complex of DNA and proteins found in the nucleus

d. the histone and non-histone proteins in eukaryotic nuclei

Summary Introduction

Introduction:

Chromatin is mostly found in the cells, comprising of the DNA (deoxyribonucleic acid), RNA (ribonucleic acid), and protein. There are three levels of chromatin organization, namely, euchromatin, heterochromatin, and high-level DNA packaging of the fiber into the metaphase chromosome.

Answer to Problem 1TYK

Correct answer:

The DNA and histone together form chromatin. The packaging of the double helical structure of DNA is done by the histones.

Explanation of Solution

Explanation/Justification for the correct answer:

Option (c) is given as the assemblage of proteins and DNA in the nucleus is called chromatin. A gene expresses itself in a number of stages in a cell. These stages are transcription and translation. Prior to transcription, the DNA remains bound with proteins in the nucleus and is called as chromatin. Hence, Option (c) is correct.

Explanation for incorrect answers:

Option (a) is given as the histone that contains the protein core of the nucleosome. The nucleosome is a part of DNA with its proteins, which consists of a small segment of DNA held together by histone proteins. This is a part of chromatin and its repeated units give rise to complete chromatin. So, it is an incorrect option.

Option (b) is given as the 30-nm fiber. The H1 histones interact with one another and with the histone proteins in the adjacent nucleosome providing them a regular position. This structure is called as 30-nm (nanometer) fiber. So, it is an incorrect option.

Option (d) is given as the histone and non-histone proteins present in the nuclei of the eukaryotic cells. The proteins that bind DNA in the nucleus in eukaryotic cells are called histones. They are a part of chromatin. The proteins other than the histone proteins in the chromatin like DNA polymerase, scaffold proteins, polycomb proteins, and heterochromatin protein 1 are called as non-histone proteins. So, it is an incorrect option.

Hence, options (a), (b), and (d) are incorrect.

Conclusion

The main function of the chromatin is to effectively package the DNA into a small area in order to fit the DNA into the nucleus of the cell. It also protects the structure and sequence of the DNA.