DNA: The Genetic Material Chapter 12

Fredrick Griffith Performed the 1st major experiment that led to the discovery of DNA as actual genetic material Experimented with Streptococcus pneumoniae which causes pneumonia He found that one strain could be transformed, or changed, into another He injected mice with 1 of 4 options – Disease causing strain into the mouse – Non-disease causing strain into the mouse – Heat killed disease causing strain into the mouse – Heat killed disease causing strain along with the non- disease causing strain into the mouse

Transforming Factor! Oswald Avery discovered it! Concluded that when the S cells in Griffith’s experiments were killed, DNA was released. The R cells picked up the DNA and incorporated it into its own DNA, changing the R cells into S cells. But there was always a question whether proteins or DNA were responsible for the transfer of genetic material

Hershey and Chase Found the answer. DNA is the transforming factor. A bacteriophage (virus that attacks bacteria) – Bacteriophage is made of DNA and protein – Viruses cannot replicate themselves. They must inject their genetic material into a living cell to reproduce They labeled both parts of the virus to determine which part was injected into bacteria. This would be the genetic material.

Radioactive Labeling and Tracking DNA 2 groups of bacteriophages One with radioactive phosphorus because proteins do not contain phosphorus, so DNA would be radioactive The other with radioactive sulfur because DNA does not contain sulfur, so the proteins would be radioactive Result was that viruses later released from the infected bacteria contained the phosphorus in the first group. No sulfur was found in the second group.

DNA Structure The “Backbone” Has 2 Parts 2 Strands called: Double Helix

DNA Structure The “Rungs”

Erwin Chargaff Analyzed amount of nitrogenous bases Focused on the “rungs” Rungs= nitrogenous bases Nitrogenous DNA bases are Adenine, Guanine, Cytosine, and Thymine – Purine bases = Adenine and Guanine – Pyrimidine bases = Cytosine and Thymine So one rung and backbone consists of a phosphate and deoxyribose, a purine, a pyrimidine, and another deoxyribose and phosphate CHARGAFF RULE: C=G and T=A

How to Remember the Nitrogen Bonds Bonds with Think AT&T phone service

How to Remember the Nitrogen Bonds Bonds with Think Half circles

Watson and Crick Built the model of the double helix from Chargoff’s data and Franklin’s x-ray. 1.2 outside strands of alternating deoxyribose and phosphate 2.Cytosine and Guanine bases pair to each other by 3 hydrogen bonds 3.Thymine and Adenine bases pair to each other by 2 hydrogen bonds

Chromosome Structure The phosphate groups in DNA create a negative charge, which attracts the DNA to positively charged histone proteins and forms a nucleosome Nucleosomes group together into chromatin fibers. They supercoil to make up the DNA structure recognized as a chromosome.

Chromosomal Structure

Replication of DNA: Semiconservative Replication Chromosome Structure: RiN84

DNA Replication Every time that cells divide to produce new cells, DNA must first be copied A single strand of DNA can serve as a template for the new strand to form Replication assures that every cell has a complete set of identical genetic information DNA is divided into 46 chromosomes that are replicated during the S phase of the cell cycle

Enzymes to the Rescue! 1.DNA Helicase unwinds and unzips the double helix 2.The hydrogen bonds between the nitrogenous bases are broken 3.Proteins called single stranded binding proteings keep the strands separate during this process 4.RNA primase comes and adds a short segment of DNA called a RNA primer. (new nucleotides can’t be added without a primer)

5. DNA polymerase comes and catalyzes the addition of nucleotides to the new DNA strand 6. DNA polymerase adds new nucleotides to the 3’ end of the new DNA strand. A to T. C to G. 7. The two unzipped strands are made in a different way. One strand is the leading strand (synthesized towards replication fork) and the other is the lagging strand (synthesize and elongates away from replication fork). Lagging strand made discontinuously into small segments called okazaki fragments. 8. Okazaki fragments later connected to one another by DNA ligase.

DNA Replication Semiconservative Replication E DNA Replication Process KoFU2Nw

Central Dogma

DNA vs. RNA RNA = Ribonucleic acid, is a chain of nucleotides, each made of sugar, a phosphate group, and a nitrogenous base – Think of RNA as a temporary copy of DNA The sugar in RNA is ribose and the sugar in DNA is deoxyribose RNA has the base uracil in place of thymine. They both pair with adenine. RNA is a single strand of nucleotides and DNA is double stranded

Transcription Happens in the nucleus The process of copying DNA to produce a complementary strand of RNA – RNA polymerase makes the new RNA strand – Using only one strand of DNA as template – RNA base pairing follows the same rules as DNA base pairing except uracil pairs with adenine. Guanine pairs with cytosine. – Once the entire gene transcribes, the RNA detaches – Then DNA helix zips back together

Transcription Transcription produces 3 major types of RNA molecules – mRNA: (messenger RNA) an intermediate message that is translated to form a protein – rRNA: (ribosomal RNA) forms part of ribosomes, a cell’s protein factories – tRNA: (transfer RNA) brings amino acids from the cytoplasm to a ribosome to help make the growing protein

Translation In the ribosomes Translation is the process that converts, or translates, an mRNA message into a polypeptide that make up a protein. Nucleotides are read in groups of 3 called codons. Each codon stands for an amino acid

Translation Ribosome pulls the mRNA strand through it one codon at a time. The complementary tRNA anticodon molecule carrying the amino acid pairs with the mRNA codon. The ribosome helps form a peptide bond between this and the next amino acid. The mRNA strand is then pulled to the next codon

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Transcription and Translation