1. Chapter 14: DNA

2. I) Genetic Material – What is it?
Stable molecule that is not easily damaged or altered
DNA has many hydrogen bonds that hold it together
Contains strong bonds in the “sugar-phosphate backbone”
Phosphodiester Bonds – bond between deoxyribiose and phosphate
Can be easily reproduced
Accurately copied by enzymes that “unzip” the double helix
Hi fidelity – very accurate to conserve genetic code of a species
Complex for variability
Four nitrogenous bases form 64 3-base codons
Many sequences of codons can code for different proteins

3. II) Experiments that Proved DNA is the Hereditary Material of Organisms
Frederick Griffith (1928)
Bacterial Transformation
Hereditary information from dead virulent bacteria was transferred into live non- virulent bacteria
Live non-virulent bacteria became virulent
Genetic Material was resistant to heat treatment – was not protein based because proteins denature in high temperatures
Avery-McCarty-MacLeod (1944)
Used heat to kill the virulent Streptococcus pneumonia bacteria and extracted RNA, DNA, carbohydrates, lipids and proteins
Each molecule was added to a culture of live non-virulent bacteria to determine which was responsible for changing them into virulent bacteria.
DNA was the only molecule that turned the non-virulent cells into virulent cells, which they concluded was the genetic material within cells.

5. Francis Crick and James Watson (1953)
Hershey and Chase (1952)
Determined the genetic material was the molecule DNA
Traced the movement of DNA from viruses into bacterial cells
Proved DNA was the molecule being transferred NOT protein
Rosalind Franklin (1952)
Studied DNA using X-Ray crystallography
Determined the double helix structure (two strands, NOT 3)
Determined the structure of the sugar phosphate backbone
Could not interpret the base pairing
Erwin Chargaff (1952)
Determined the ratio of DNA bases to be equal
A = T C = G
Ratios are also species specific
Francis Crick and James Watson (1953)
Determined the base pairing of DNA
Used Franklin’s data to help determine the overall structure
Proposed how DNA could replicate by “unzipping”
Could not have done their work without Franklin’s results

6. Hershey and Chase Experiment

7. Rosalind Franklin’s X-Ray Diffraction

8. Chargaff’s Rule
Humans: 60% A-T 40% C-G Wheat: 55% A-T 45% C-G

9. James Watson and Friends

10. Watson and Bolen

11. Messelson and Stahl (1958) Determined how DNA replicates
Modeled semiconservative replication
The old or template strand is copied and becomes part of the new DNA molecule

12. III) DNA Structure
DNA, and in some cases RNA, is the primary source of heritable information.
1. Double Helix
Two alpha helices of deoxyribonucleic acid
Contains repeating subunits called nucleotides
Phosphate, sugar, nitrogenous base
2. Bonding
Hydrogen bonds BETWEEN the nitrogenous bases
Many weak bonds results in collectively strong bonding
Phosphodiester Bonds
Strong bonds in sugar-phosphate backbone
3. Complementary (opposite) Base-Pairing
Adenine and Thymine pair
Cytosine and Guanine pair
Result of specific hydrogen bonding between bases
Purines: Adenine and Guanine
Pyrimidines: Cytosine, Uracil, Thymine (PYRamid stones were CUT)
One side of the double helix complements the other side

15. 4. Antiparallel Helices
Each side of the DNA molecule is oriented in the opposite directions
Permits base pairing
Important in understating direction of replication and location of enzymes and other proteins
Based upon the numbering of
the carbons in the deoxyribose
molecule

16. 5. Semiconservative Replication
Each DNA molecule is copied from the original strand
Two copies of DNA produced in replication
Each strand contains half new and half template DNA

17. IV) DNA Replication
Genetic information is transmitted from one generation to the next through DNA or RNA
Non-eukaryotic organisms have circular chromosomes
One replication origin
Eukaryotic organisms have multiple linear chromosomes
Multiple replication origins
Exceptions to this rule:
Plasmids - small extra-chromosomal, double-stranded circular DNA molecules
Prokaryotes, viruses and eukaryotes can contain plasmids

18. Eukaryotic Chromosome Structure

19. New DNA molecules are synthesized from a template or original DNA strand
Topoisomerase – relaxes the supercoiling of DNA
Gyrase – relieves strain on the helix as it is uncoiled
DNA Helicase – breaks hydrogen bonds between nitrogenous bases
DNA Primase – forms a primer of RNA in the 3’5’
Starting point for DNA polymerase to attach and begin copying
DNA Polymerase – synthesizes new DNA from template
“Reads” and moves along the DNA template in the 3’  5’ direction
Adds nucleotides to the 3’ ends of the DNA template
Exonucleases – remove incorrect DNA bases
DNA polymerase I can move backwards one base to remove errors
Ligase – links Okazaki fragments on the lagging strand
Lagging strand – new DNA produced in short segments
Leading strand – new DNA produced in one continuous strand

20. Bi-Directional Replication in DNA 1 Bi-Directional Replication in DNA 2 Replication 3 Replication 4

21. IV) Special Cases of DNA Replication
Retroviruses
Genetic information in retroviruses is a special case and has an alternate flow of information: from RNA  DNA
Reverse transcriptase - enzyme that copies the viral RNA genome into DNA.
This DNA integrates into the host genome
Viral genes become transcribed and translated for the assembly of new viral progeny.
Examples of retroviruses: HIV,