1. Chapter 12
DNA

2. Ch DNA
DNA Model
Rosalind Franklin was able to produce a picture of DNA using a procedure called
X-ray crystallography

3. Ch. 16 - DNA DNA Model (cont.)
From this image, James Watson and Francis Crick were able to generate a model of DNA
In their model:
1) DNA was a helix
2) DNA was made of two strands that went in opposite directions
3) the two strands were held together by chemical bonding between nitrogenous bases
The later determined that adenine (A) always bound to thymine (T) and cytosine (C) always bound to guanine (G)

4. DNA and Chromosomes Eukaryotic Chromosome Structure Chromosome
Nucleosome
DNA double helix
Coils
Supercoils
Eukaryotic chromosomes contain DNA wrapped around proteins called histones. The strands of nucleosomes are tightly coiled and supercoiled to form chromosomes.
Histones

5. DNA Located on chromosomes in the nucleus.
Chromosomes have DNA and protein tightly packed together called
chromatin.
Chromatin consists of DNA tightly coiled around proteins called histones.
DNA and histones together form nucleosomes.

6. Ch. 16 - DNA DNA holds the genetic material of living organisms
Sugar–phosphate
backbone
Nitrogenous
bases
DNA holds the genetic material of living organisms
DNA is a polymer made of several nucleotides
Each nucleotide consists of
1) Sugar
2) Phosphate group
3) Nitrogenous base
Thymine (T)
Adenine (A)
Cytosine (C)
DNA nucleotide
Guanine (G)

7. DNA
4 types of
bases
Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)

8. 5 end
Hydrogen bond
3 end
1 nm
3.4 nm
3 end
0.34 nm
5 end
Key features of DNA structure
Partial chemical structure
Space-filling model

9. Ch. 16 - DNA DNA Replication
Watson and Crick suggested that the double helix structure of DNA provides a copying mechanism for DNA
They suggested that since each strand of the helix is complementary, they could be used as a template for new DNA
Therefore, when new DNA is made, each new strand of DNA consists of ½ “old” DNA and ½ “new” DNA