1. The History of DNA

4. History of DNA Discovery
In 1928, Griffith was working with smooth (S, virulent) and rough (R, non- virulent) strains of a pneumonia-causing bacterium
He performed four experiments

5. In 1944, Avery showed that the substance was DNA.

6. Hershey & Chase
Hershey and Chase confirmed that DNA is the hereditary material (not protein).

9. You are required to know this structure
Components of DNA
You are required to know this structure
DNA is composed of four kinds of nucleotides, each of which consists of:
A five carbon sugar (deoxyribose)
A phosphate group (PO4-)
One of four bases
Adenine (A)
Guanine (G)
Thymine (T)
Cytosiine ©

14. She concluded: DNA exists as a long, thin molecule of uniform diameter
The structure is highly repetitive
DNA is helical

17. Watson & Crick used numerous sources of data to build models of DNA

18. The following features were incorporated into their model
The bases were hydrogen bonded (a weak bond) together in the center of the helix
-T (a pyrimidine) had two hydrogen bonds with A (a purine)
-C (a pyrimidine) had three hydrogen bonds with G (a purine)

19. The backbone was made of chains of deoxyribose sugar covalently bonded (a strong bond) to phosphate groups.
The phosphate group is bonded to the 3’ carbon of one deoxyribose, and the 5’ carbon of another.
5’ Carbon
Covalent bond
3’ Carbon
Covalent bond

20. Each sugar of the backbone is covalently bonded to the nitrogenous base off of carbon 1

21. There are 10 base pairs per turn of the helix.

22. The two sides are anti- parallel, meaning that the sugar and phosphates are running in opposite directions.
Each side ends in a phosphate (5’end) and a sugar (3’ end)
Since the sides are anti- parallel, one side goes in the 3’ to 5’ direction, and the other goes in the 5’ to 3’ direction.

24. The base pairing is constant for all species, but the sequence of base pairs in a nucleotide strand is different from one species to the next.
These are some of the genomes that have been sequenced to date.

25. Where is DNA located? Prokaryotes (bacteria and Archaea)
Circular DNA in a region called the nucleoid
Plasmid

26. Where is DNA located? Eukaryotes Inside the nucleus Linear
Highly coiled

27. Nucleosome A section of DNA that is wrapped around a core of proteins.
DNA forms a complex with proteins called chromatin, which allows the DNA to be condensed to a smaller volume.
When the chromatin is extended & viewed under a microscope, the structure resembles beads on a string.
Each tiny beads is called a nucleosome.

28. Inside mitochondria and chloroplasts
Circular
“naked” not associated with protein