D N A
DNA is located in the cell's nucleus a. The structure of
DNA is essential to its function and replication b.
Location of the DNA in a cell
2. Electron micrograph of a
nucleus showing the chromatin
that contains the DNA. In a
non-dividing cell, the DNA is
unwound in the chromatin, like
a long ribbon.
about 10,000x CSM
Light micrograph of a
non-dividing cell (outlined)
showing the nucleus
DNA double helix
3. Light micrograph of a
dividing cell (outlined)
showing the condensed
4. When a cell divides,
the DNA gets wound
around histone proteins
into nucleosomes, which
get tightly packaged into
DNA is the cell’s genetic material. It contains all the information
necessary to make another cell or organism.
In a non-dividing cell, it is found in the nucleus as chromatin.
In a dividing cell, the nucleus disappears and the chromatin
condenses into chromosomes.
Nucleic Acids Carry Genetic Instructions
Nucleic acids (noo-KLE-ic) were first discovered in the
nuclei of cells (Figure 2.14a). They are huge organic
molecules that contain carbon, hydrogen, oxygen, nitro-
gen, and phosphorus. A nucleic acid molecule is composed
of repeating building blocks called nucleotides (Figure
2.14b). Each nucleotide consists of three parts:
40 CHAPTER 2