1. The Structure of DNA

3. What is DNA?
It is a nucleic acid that contains deoxyribose sugar and holds an organisms genetic information
DNA achieves its control by producing proteins called enzymes

4. Structure of DNA
In the 1950’s, Rosalind Franklin used a technique called X-ray diffraction to get information about the structure of DNA
The x-ray pattern revealed the X-shaped pattern and gave clues that the DNA strands are twisted
The twisted shape is known as a helix
James Watson and Francis Crick used Franklin’s x-ray to develop a model of the DNA structure

5. Description of the DNA molecule
DNA is a polymer of repeating subunits called nucleotides arranged in a double helix
Nucleotides have three basic parts:
5 carbon sugar called deoxyribose
Phosphate group
Nitrogenous base
The deoxyribose sugar and phosphate groups form the backbone of a DNA chain in an alternating pattern
The nitrogenous bases are attached to the deoxyribose sugar which stick out sideways from the chain

6. Description of the DNA molecule
Four nitrogenous bases in DNA
Adenine
Guanine
Cytosine
Thymine
Adenine bonds to Thymine by forming hydrogen bonds
Cytosine pairs with Guanine in the same way
Purines (double rings)
Pyrimidines (single ring)

7. Solving the Structure of DNA
When trying to understand the structure of DNA, one scientist Erwin Chargaff discovered that the percentages of adenine (A) and thymine (T) were almost equal and that the same was true of guanine (G) and cytosine (C)
The observation that A = T and G = C became known as Chargaff’s rule

8. Chromosomes
and
DNA

9. Where is DNA found? In prokaryotic cells In the cytoplasm of the cell
In eukaryotic cells
In the cytoplasm of the cell
It is also referred to as the chromosome
one
In the nucleus
In the chromosomes
more than one

10. Chromosome Structure What is a chromosome?
What does it look like?
A threadlike structure within the nucleus containing genetic information
DNA and proteins (histones) tightly coiled into beadlike structures called nucleosomes that loop around

11. Chromosome structure