Chapter 12, Problem 2A

Summary Introduction

To determine:

To replace the underlined word in a sentence to make it correct.

Introduction:

DNA stands for Deoxyribonucleic Acid. It is an organic compound and it has a unique molecular structure. It is found in all prokaryotic cells and eukaryotic cells.DNA is a long polymer of nucleic acids and these nucleic acids are made by the arrangement of nitrogenous bases, sugar molecules and the phosphate groups that are linked by different bonds in a series of sequences.

Answer to Problem 2A

The word which can be filled to replace double helix is nucleosome. So the correct sentence is “A nucleosome consists of DNA wrapped around histone protein”.

Explanation of Solution

DNA as an acidic substance present in nucleus was first identified by theFriedrich Miescher in 1869 during his research on white blood cells.He named DNA as “Nuclein”.

The packaging of DNA in eukaryotes is complex. In eukaryotes, there is a set of basic positively charged proteins called histones. These histones are rich in basic amino acids arginine and lysines. Histones are organized to form a unit of eight molecules called histone octamer. The negatively charged DNA is coiled around the positively charged histone octamer to form a structure called nucleosome. A typical nucleosome contains 200 base pairs of DNA helix.