DNA and The Central Dogma

Discovery - ExperimentsFrederick Griffith – Transformation Happens

Through ChemicalsInjected Mice With Strains of Pneumonia…

Live R Cells: livedLive S Cells: diedPasteurized S Cells: livedLive R with dead S cells: diedConclusion: 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

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)

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.

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

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

Central DogmaDNA RNA Polypeptides/Proteins Traits- Protein synthesis

- Transcription DNA RNA- Translation RNA

Polypeptides/Proteins

- Expression Proteins traits

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)

TranslationStart- 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 siteProcess- Elongation/Elongation factors- rRNA- Peptide Bonds- TranslocationTermination- Stop codon- Release factor- PolyribosomesEct.- Primary, secondary, tertiary, quarternary structures

Click here for a full explanation of transcription and translation:https://www.youtube.com/watch?v=itsb2SqR-R0

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

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=10YWgqmAEsQ

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)

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