1. THE HISTORY OF DNA FRIEDRICH MIESCHER (1869)
Discovered a nonprotein substance in the nuclei of pus cells
Named the substance “nuclein”

2. Joachim Hammerling (1930’s)
Experiments with the green algae Acetabularia showed that the regeneration of appendages required the nucleus which was located in the foot
Suggested that genetic information is stored in the nucleus

3. Chemical analysis showed that:
A = T and G = C
A + G = T + C
Complementary base-pairing
Erwin Chargaff (1949)

4. Alfred Hershey and Martha Chase (1952)

5. Their experiments showed that DNA tagged with radioactive phosphorus (32P) was found inside infected bacterial cells and directed the synthesis of new viral DNA and new viral protein coats
Protein coats tagged with radioactive sulfur (35S) did not enter bacterial cells
Suggested that DNA is the hereditary material

6. Rosalind Franklin (1953)
X-ray diffraction showed that DNA was in the shape of a double helix

7. Watson and Crick (1953)

8. Watson and Crick deduced the model of DNA that persists today:
Double helix, clockwise (right-handed helix)
1 complete turn every 10 nucleotides (3.4 nm full helical twist)
Sugar-phosophate backbone
Complementary base-pairing between nucleotides – hydrogen bonding
Constant diameter of 2nm
Antiparallel strands

9. DNA STRUCTURE

10. The Chemical Composition of DNA
Composed of nucleotides held together by phosphodiester bonds
Each nucleotide consists of a deoxyribose sugar, a phosphate group and a nitrogenous base

11. Deoxyribose sugar

12. 4 Nitrogenous Bases Pyrimidines (single rings) Thymine Cytosine
Purines (double rings)
Adenine
Guanine

13. Sugar-Phosphate backbone
Phosphodiester bonds hold the sugar-phosophate backbone together
Each DNA strand has a 5’ end (attached to a phosphate group) and a 3’ end (attached to a hydroxyl group)

14. Hydrogen bonding occurs between complementary base pairs.

15. DNA Molecule DNA is a double helix
The two strands run “antiparallel” to one another
Hydrogen bonds hold the complementary bases together

16. Writing DNA sequences:
Every DNA molecule has “directionality” and bases sequences are written as follows:
e.g.) 5’ – ATGCCGTTA – 3’
3’ - TACGGCAAT – 5”
(Usually, only the 5’ to 3’ strand is written since the complementary strand can be deduced.)

17. What attributes of DNA’s structure enable it to be replicated?
Complementary base-pairing
Hydrogen bonds between base pairs
Double stranded, therefore, each strand can serve as template for the replication of the complementary strand

18. Gene Organization and Chromosome Structure

19. Define These Terms Gene Chromosome Histone Chromatin
Metaphase chromosome
Chromatid
Centromere

20. Gene – a sequence of nucleotides that codes for a protein
Chromosome – one continuous double-stranded DNA molecule
Histone – a positively charged protein that binds to negatively charged DNA
Chromatin – complex of DNA and histones located in the nucleus of eukaryotic cells
Metaphase chromosome – a duplicated chromosome
Chromatid – one half of a duplicated chromosome
Centromere – a constricted region that holds two replicated chromosomes together