1. Experiments in the 1940s-1950s identified DNA as the genetic material that carries hereditary information and is passed from parents to offspring. 2. The structure of DNA was discovered in 1953 - it exists as a double helix with a backbone made of alternating sugar and phosphate groups joined by nucleotides that pair up following Chargaff's rules. 3. DNA replication was discovered in the late 1950s - it occurs in a semi-conservative manner as the double helix unwinds and each strand acts as a template to produce two identical copies of DNA.

1. DNA and The Central Dogma

2. Discovery - Experiments
Frederick Griffith – Transformation Happens Through
Chemicals
Injected Mice With Strains of Pneumonia…
Live R Cells: lived
Live S Cells: died
Pasteurized S Cells: lived
Live R with dead S cells: died
Conclusion: Dead S cells can give genetic material to live R
cells, making them harmful
Avery, MacLeod, McCarty – DNA is Transforming Factor
- used isolated DNA & RNA, narrowed down chemicals in
bacteria
- discovered that DNA caused transformation
- however, people thought transformation applied only to
bacteria

3. Hershey & Chase– Confirmation that DNA is Transforming
Factor
- used radioactive sulfur (proteins) and phosphorus (DNA) to
track which caused transformation with viruses
- in result found only the radioactive phosphorus in the
bacteria (protein capsid didn’t enter the cell)
- confirmed DNA is the transforming factor
Franklin, Wilkins, Waston, & Crick – Structure of DNA as
Double Helix
- Rosalind Franklin used X-ray crystallography to photograph
DNA
- Wilkins, Watson, & Crick created a model
- double helix with a sugar-phosphate backbone
bonded together covalently
- nucleotide bases follow Chargaff’s Rules
- alternates between purines (A,G) and pyrimidines
(C,T,U)

4. Meselson & Stahl – Semiconservative Replication Model
-Three different models were proposed to explain the process
of DNA replication. The Conservative and Dispersive models
were incorrect.
- According to the semiconservative model, the original DNA
strand used in replication remains intact while the new strand
is completely new.

5. Viruses
- Consists of a capsid, plasma envelope, RNA, and
nucleic acids
- Can either be a DNA virus or an RNA virus
- Bacteriophages: viruses that infect bacteria
Lytic Cycle
- Phage replication cycle that culminates in the death of the
host cells
- Similar to a factory where the virus uses the materials of
the cell to multiply then burst from the cell (lysis)
- Example: Influenza
Lysogenic Cycle
- DNA becomes part of the cell and remains dormant until
triggered wherein it proceeds the same as the lytic cycle
- Each time the host cell reproduces, the genetic material of
the virus reproduces with it.
- Example: The herpes simplex virus

6. DNA Replication
- Involves the separation of a DNA molecule into two
strands that are template strands to assemble a new
complementary strand
- results in two identical double stranded molecules of DNA
in a semi-conservative model with one new strand and one old
strand
- Origin of Replication
- replication bubble
- Topoisomerase
- Replication Fork
- Helicase
- single stranded binding proteins
- Primase
- DNA Polymerase
- leading complementary strand
- lagging complementary strand
- Okazaki fragments
- DNA Ligase
Click here for a complete explanation of DNA replication:
https://www.youtube.com/watch?v=8kK2zwjRV0M

7. Central Dogma
DNA  RNA 
Polypeptides/Proteins  Traits
- Protein synthesis
- Transcription DNA  RNA
- Translation RNA 
Polypeptides/Proteins
- Expression Proteins  traits

8. Transcription
- Transcription Factors
- RNA Polymerase
- Promoter/TATA box
- Transcription initiation complex
- 5’3 direction
- Transcription unit
- Uracil in RNA
- Polyadenylation sequence (AAUAAA)/ Terminator
- 5’ cap/poly A tail
- RNA processing/RNA splicing
- Spliceosomes
- Introns/exons
- snRNP’s (small nuclear ribosomal nuclear proteins)

9. Translation
Start
- Triplets/Triplet code
- Codons
- Reading frame
- 5’3 direction
- tRNA (aminoacyl tRNA synthetases)
- Anticodons
- Wobble
- Initiator tRNA/Start codon
- Small and large ribosomal subunits
- Translation initiation complex
- E, P, A site
Process
- Elongation/Elongation factors
- rRNA
- Peptide Bonds
- Translocation
Termination
- Stop codon
- Release factor
- Polyribosomes
Ect.
- Primary, secondary, tertiary, quarternary structures
Click here for a full explanation of transcription and translation:
https://www.youtube.com/watch?v=itsb2SqR-R0

10. Mutations
- Point mutations
- Silent mutation: A mutation, usually a
substitution, in which the mutated codon (or
codons) still code for the same amino acid,
which causes no change in the finished protein
- Missense mutation: A mutation in which a
single base is changed, and changes one
amino acid into another
- Nonsense mutations: A mutation in which a
single base is changed, changing a codon to a
stop codon
- Frameshift mutations: An alteration of the
number of bases. These are the most drastic
because they change he entire structure of the
protein, rather than just one amino acid.
- Deletion/Addition

11. Operons
- means “operate”
- found mostly in prokaryotes
- P.R.O.G. (Promoter Repressor Operator
Gene)
- Lac Operons (inducible)
- TRP operons (repressible)
Click here for an in-depth explanation of
operons:
https://www.youtube.com/watch?v=10YWgqmA
EsQ

12. Prions
- Not cells or viruses
- Misfolded versions of a protein
- Normally found in the brain
- Infectious
- Cause of several brain diseases: scrapie (sheep), mad
cow disease (cattle), Creutzfeldt-Jakob disease
(humans)

13. Transposons
- “jumping genes”
- Discovered by Barbara McClintock, who was
studying the genetics of corn in the 40’s and 50’s
- Jump in a “cut and paste” fashion from one part
of the genome to another
- Two classes of jumping genes: insertion
sequences and complex trasposons