1. DNA Structure & Function

2. What is DNA?
DNA: Deoxyribonucleic Acid carries genetic information (genetic code) and controls cellular functions
All living things have DNA that only differs in the sequence of nucleotides.

3. DNA - In eukaryotes, DNA is located in the nucleus.
- In prokaryotes, the DNA is a loop, which is not contained in a nucleus but found in an area called the nucleoid region

4. History of DNA

5. Discovery of DNA
In 1928 Fredrick Griffith did experiments trying to find a vaccine for pneumonia; he discovered that when harmless bacteria and a virulent (disease-causing) bacteria were mixed together, some of the harmless bacteria became virulent.
He called this process transformation

6. History of DNA
Transformation: the ability of one organism to be permanently changed by another through the exchange of DNA

7. Discovery of DNA In 1944 Oswald Avery repeated
Griffith’s experiments but he used enzymes enzymes to remove proteins, lipids,
RNA & DNA separately.
- Transformation occurred each time except when DNA was removed, so DNA must be the transformation factor.
DNA is the genetic material that stores and transfers genetic information from one generation of an organism to another

8. Discovery of DNA
During the 1950’s, most scientists still thought that proteins carried genes.
In 1952, Alfred Hershey and Martha Chase did a series of experiments with bacteriophages & discovered that DNA is the source of genetic information that proved Avery’s transformation principle.

9. History of DNA
Bacteriophage: viruses that attack bacteria, composed of DNA or RNA core and a protein coat
Hershey and Chase confirmed that DNA was the genetic molecule of inheritance in organisms and not proteins

10. History of DNA
When Hersey & Chase used radio active markers to mark the protein coats of the bacteriophages, the infected bacteria didn’t become radio active.
Repeated with radioactive markers on the DNA of bacteriophages, the infected bacteria became radioactive.

11. Discovery of DNA
In 1952, Rosalind Franklin developed special X-ray diffraction experiments to study the structure of the DNA molecule
These X-ray patterns showed an X-pattern with 2 strands of DNA twisted around each other. DNA resembled the coils of a spring.

12. Discovery of DNA
In 1953, James Watson and Francis Crick described the shape and structure of DNA (with the help of previous X-ray experiments from Franklin)
Through the construction of a model, they proposed the structure of DNA that is known as double helix.

13. History of DNA

15. Nitrogen Bases
[A] & [G] – belong to a group of compounds called purines (double ring of carbon)
* [T] & [C] – belong to a group of compounds called pyrimidines (single ring of carbon)

16. Watson & Crick discovered that it was a double helix shape, with a sugar phosphate backbone, connected in the middle with nitrogen bases.
T binds with A, & G binds with C: base paring

17. Structure of DNA The monomer of DNA is a nucleotide
A nucleotide consists of 3 main parts:
1. Phosphate group
2. 5 carbon sugar (deoxyribose)
3. Nitrogen base
- Adenine [A]
- Guanine [G]
- Thymine [T]
- Cytosine [C]

18. Structure of DNA
Phosphate and sugar make up the backbone or sides of the DNA molecule
Nitrogen bases pair up to form the center
These base pairs are held together by weak hydrogen bonds

19. Discovery of DNA
- Erwin Chargaff experimented with DNA and observed that in each organism the amount of the 4 nitrogen bases was equal. Although, the amount of DNA was different between different types of organisms
His experiments resulted in the base pairing rule :
[A] = [T] and [G] = [C]

20. Antiparallel (see how one side is upside down)
Phosphate-sugar backbone linked with covalent bonds
Nitrogen bases linked with hydrogen bonds

21. DNA
DNA can hold a great deal of information because it is a very long molecule.
Living things are different because the sequence (order) of the nucleotides is limitless.
The more similar the sequence, the more closely related the organisms.

22. Chromosomes & Replication

23. DNA Length
Very long
E. coli: over 4.6 million nucleotides, but must fit in a cell 1/1000 in length
Eukaryotes: varies by species, but can be 1000 times longer than prokaryotes
Humans over 1 m of DNA in each cell

24. Chromosome Structure
Prokaryotes: DNA is folded into a single loop chromosome
Eukaryotes: DNA is folded around proteins (histones) and coiled to form multiple chromosomes
Humans have 46 chromosomes in each cell

25. Replication
Every cell must contain an identical copy of DNA so it must be replicated before new cells form.
Prokaryotes: starts at 1 “point of origin” and continues around the loop chromosome
Eukaryotes: hundreds of points of origin

26. DNA Replication DNA needs to replicate itself, which means it
needs to make an
exact copy of itself
to pass along to the
daughter cell during cell division
1 DNA molecule > 2 identical DNA molecules
Occurs in the nucleus prior to cell division (in the cytoplasm of a prokaryote)

27. Replication Separate the DNA Stands
The enzyme helicase breaks the hydrogen bonds to open the DNA strand like a zipper

28. DNA Replication
The split where it unzips is called the replication fork

29. DNA Replication Replication happens in the 5’----> 3’ direction
It is semiconservative, meaning that every double-stranded molecule of DNA has one strand that is “old” and one strand that is “new”
Replication can occur at hundreds of different replication forks all at the same time on the same molecule

30. DNA Replication
2. Another enzyme called DNA polymerase pairs “free” complimentary nucleotides found in the nucleus to each side of the original unzipped strand.
New hydrogen bonds form between the nitrogen bases.

31. Replication Nucleotides are added
When the enzyme called DNA polymerase adds nucleotides, it uses the original DNA strand as a template.
DNA polymerase can only add in the 5’ to 3’ direction
Leading strand: (5’ to 3’) continuously adds nucleotides
Lagging strand: (3’ to 5’) creates small sections called Okazaki Fragments as the DNA opens
Enzyme DNA ligase joins Okazaki fragments together

32. DNA Replication
This process takes time as the lagging strand has to wait for the DNA to unzip and then fill in backwards a little section at a time making it “grow” in the wrong direction (away from the replication fork).
The Okasaki fragments are joined into a single strand by an enzyme called DNA ligase
Ultimately, the overall direction of “growth” is toward the replication fork but it must be done in small segments that require the lagging strand to fill in away from the fork

33. DNA Replication
3. This continues until the entire strand has been copied. The results are two identical strands of DNA.

34. Overall Direction of DNA Replication is Towards the Replication Fork
One strand, called the leading strand, grows in the 5’ to 3’ direction towards the replication fork

35. DNA Replication
Other strand called the lagging strand, is created next to the 3’--->5’ strand
this lagging strand must add nucleotides in short 5’ --->3’ away from the replicating fork in segments called Okazaki fragments

36. DNA Replication

37. DNA Replication

39. Replication fork opens in both directions 

41. Gene Regulation
Not all genes are used in every cell. Genes can be turned off (silenced)
In prokaryotic cells groups of genes that are turned on/off together are called operons

42. Gene Regulation Eukaryotic Cells
Genes can be turned on by enhancer and promoter sequences
Genes can be turned off by repressor proteins
Cell Differentiation: cells in multicellular organisms have to change in order to do different jobs. All cells have all of the exact DNA, but only parts of the DNA are expressed.

43. DNA Replication http://www.youtube.com/watch?v=hfZ8o9D1tus