DNA Molecular Genetics

DNA’s Discovery was a Collaborative Work 1. Frederick Griffith's Experiment - the discovery of transformation Using two varieties of streptococcus, he originally searched for a vaccine. One variety of bacteria had a capsule (like a cell wall) the other did not have a capsule. 1. Injection with live encapsulated bacteria -- mice contracted pneumonia and died 2. Injection with live naked(no capsule) bacteria -- mice lived, immune system destroyed the bacteria 3. Injection with heat killed encapsulated bacteria -- mice remained healthy 4. Injection with dead encapsulated bacteria and live naked bacteria -- mice contracted pneumonia and died *note that neither of this forms caused disease before, but when placed together something occurred to make the living naked bacteria virulent. Conclusions: Living bacteria acquired genetic information from dead bacteria - particularly the instructions for making capsules, thus transforming the naked bacteria into encapsulated bacteria. The Transforming agent was discovered to be DNA. DNA was isolated and added to live naked bacteria, and they were transformed into the encapsulated kind.

The Hershey-Chase Experiment - Bacteriophage 1. Hershey and Chase forced one population of phages to synthesize DNA using radioactive phosphorous. 2. The radioactive phosphorous "labeled" the DNA. 3. They forced another group of phages to synthesize protein using radioactive sulfur. 4. The radioactive sulfur "labeled" the protein. 5. Bacteria infected by phages containing radioactive protein did not show any radioactivity. DNA contains phosphorous but not sulfur. Proteins contain sulfur but not phosphorous 6. Bacteria infected by phages containing radioactive DNA became radioactive. 7. This showed that it was the DNA, not the protein that was the molecule of heredity

Base-Pairing Rules Chargaff analyzed the amounts of the four nucleotides found in DNA (Adenine, Thymine, Guanine, Cytosine) and noticed a pattern. 1.  The amount of  A, T, G, C varies from species to species 2.  In each species, the amount of A = T, and the amount of G = C  ----   Base Pair Rule Bases come in two types: pyrimidines (cytosine and thymine) and purines (guanine and adenine)

X-Ray Diffraction Studies Rosalind Franklin and Wilkins spent time taking X- ray diffraction pictures of the DNA molecule in an attempt to determine the shape of the DNA molecule.

Watson & Crick Watson and Crick  are credited with finally piecing together all the information previously gathered on the molecule of DNA. They established the structure as a double helix - like a ladder that is twisted. The two sides of the ladder are held together by hydrogen bonds.   

Summary of Research Griffith and Transformation- Something transformed the bacteria into deadly bacteria. Hershey and Chase- DNA is the molecule of heredity Chargaff- A goes with T and C goes with G Franklin- It’s a double helix Watson & Crick- Put all the information together.

The Structure of DNA DNA = Deoxyribonucleic Acid Phosphate Sugar = Deoxyribose Nitrogenous Bases Hydrogen Bonds 1 Nucleotide = 1 phosphate + 1 sugar + 1 nitrogenous base

Nitrogenous Bases A = Adenine bonds to T. Needs 2 Hydrogen Bonds. G = Guanine bonds to C. Needs 3 Hydrogen Bonds. T = Thymine Bonds to A. Needs 2 Hydrogen Bonds. C = Cytosine Bonds to G. Needs 3 Hydrogen Bonds. Purines = Larger Molecules A & G Pyrimidines = Smaller Molecules C & T Need to be a certain size to fit perfectly between the two vertical backbones 1 purine + 1 pyrimidine = perfect size

DNA Replication: - Whenever a cell divides it makes another copy of itself so one copy can go to each daughter cell = IT REPLICATES Occurs in S phase of interphase DNA separates (unzips) into 2 strands - Each strand has certain bases that determine what will be on the new strand. - The 2 original strands are Complementary - The strand is unzipped by a molecule called a helicase

2) When the DNA is split into a 2 prong replication fork the molecule DNA Polymerase builds the new complementary strand using the old strand as a template. (what is a template?)

DNA Polymerase also proofreads the strand to prevent errors - Each new double helix is made up of 1 old half and 1 new half = DNA Replication is Semiconservative - That means it is “half-way” conserved.

Ribonucleic Acid (RNA) Used in the production of proteins Different from DNA A) The sugar is Ribose instead of Deoxyribose B) Uracil is used instead of Thymine. - Uracil bonds to Adenine with 2 hydrogen bonds. A = U - There is no thymine in any of the types of RNA.

Transcription A lot like Replication, only instead of making more DNA you make mRNA m = Messenger. Messenger RNA is a copy of the instructions needed to make a protein. Proteins are made by the ribosomes in the cytoplasm of the cell mRNA acts as a messenger that takes the instructions on how to build a protein from the DNA in the nucleus to the ribosomes in the cytoplasm.

Transcription A helicase unzips the DNA RNA Polymerase needs to find a start codon (3 bases in a row). This is how it knows where to start copying = TAC - The promoter sequence

Transcription RNA Polymerase will keep copying until it gets to a stop codon or termination sequence. ATT, ATC, ACT. - Transcription starts with one double-strand of DNA and results in one single-stranded mRNA molecule.

Translation The information from the DNA is translated into a protein Occurs in the ribosomes in the cytoplasm Ribosomes are made of pieces of rRNA or = ribosomal RNA 1) Protein translation Begins when the mRNA brings a promoter sequence to the ribosome = AUG

Translation The ribosome moves down to the next three letter codon on the mRNA and attaches the correct tRNA anticodon. tRNA = Transfer RNA

Codon Charts: The tRNA brings a single Amino Acid to add to the growing chain.

Translation This process will continue until the ribosome encounters one of the stop sequences: - UUA, UAG, UGA - The protein is now complete

Follow the Storyline of the Three Types of RNA mRNA rRNA tRNA http://www.youtube.com/watch?v=NJxobgkPEAo http://www.youtube.com/watch?v=yJdAxuIA6QM&fe ature=related