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Chapter 8 Notes

Ch 8 Main
DNA Synthesis
Protein Synthesis
  1. List the events that led scientists to identify the genetic material
  2. Summarize how scientists determined the structure of DNA
  3. Describe the structure of the DNA molecule
  4. Summarize the process of DNA replication
  5. Summarize the process of gene expression
  6. Describe how RNA is made
  7. Explain why the genetic code is said to be universal
  8. Explain the relationships among codons. Anticodons and amino acids
  9. Explain why cells must regulate gene expression
  10. Summarize how a gene can be switched on and off
  11. Distingush between exons and introns
  12. Explain how transposons affect gene expression
  1. Understanding DNA

     A.  How scientists identified Genetic Material

    1. Scientists set out to determine the chemical structure of DNA by studying bacteria
    2. The bacterium is called pneumococcus
    3. One strain was virulent (disease causing) the other nonvirulent
    4. An English biologist named Fredrick griffith discovered that one form of this bacteria produced colonies of bacteria that were smooth
    5. He discovered that another type of this bacteria produced rough colonies
    6. The two bacterium were injected into different colonies of mice
    7. The mice injected with smooth strain of bacterium killed the mice, the rough did not.
    8. The smooth was virulent
    9. Griffith heat killed some of the smooth strain and mixed it with rough strain and injected this into the mice. Remember, the rough is nonvirulent and was the only living form of the bacteria in the mouse
    10. The mice with the mixed injection died
    11. He took some of the bacteria that were supposed to be nonvirulent and examined them
    12. His conclusion was that the rough nonvirulent form was changed to virulent. They took something from the heat killed bacteria
    13. The process Griffith discovered is called transformation. This occurs when bacteria take up foreign DNA
    14. In 1944 a New York Scientist named Oswald Avery looked at Griffiths study
    15. Avery wanted to discover what caused the tranformation to take place. Was the substance DNA or protein?
    16. Later Avery an enzyme that distroyed proteins to one bacterial colony, and DNA distroying enzymes in another colony.
    17. The colony that had their proteins destroyed by the enzymes still became virulent, while the DNA destroyed was nonvirulent
    18. Another experiment done in New York by two scientists named Hershey and Chase worked with Bacteriophage
    19. The bacteriophage, a virus that infect bacteria, was labled with a radiocacive marker
    20. On one kind of phage, the DNA was labled, on another the Protein coat was labled
    21. They infected the bacteria and removed the protein coat of the now empty virus, the labled and unlabled coats were still there
    22. They then looked at the bacteria that had the radioactive DNA, they produced radioactive virus
    23. This proved without a doubt that DNA was the unit of inheritance

       B.   How Scientists determined the structure of DNA

    1. Scientists up to the 1950ís knew that DNA was made up of long strands of nucleotides
    2. There are 4 nucleotides in DNA, Adenine, Guanine, Cytosine and thymine
    3. Each base is made of a sugar (deoxyribose), a phosphate group and a nitrogenous base.
    4. Each type of nucleotide is named for the base that it carries
    5. There are two larger bases, purines (Adenine and Guanine): and two smaller bases, pyrimadines (cytosine and Thymine)
    6. A technique called X-Ray Diffraction determined that DNA was in a Spiral called a double Helix
    7. In 1962, James Watson and Francis Crick built the first model of DNA and this model won them the Nobel Prize
    8. Each strand has a sugar phosphate backbone ande bases. Purines are paired with pyrimadines in a specific way. A-T, C-G

         C.  How DNA is copied

    1. Before a cell can divide, it must replicate its DNA
    2. It does this by "unzipping at one end breaking the bond between the two strands
    3. As the enzyme, DNA Polymerase, begins to copy the bases, it makes sure that all original Thymines have new Adenines added, New cytosines with old Guanines etc.
    4. Using an old strand to make a new strand is called semiconservative replication
    5. This type of replication preserves the way that the bases are constructed
    6. There is old and new strand together. A copy and an original
    7. Sometimes the wrong base is added which if not caught by DNA ligase and replaced with a correct base by DNA polymerase, a mutation may occur
    8. When all is finished, a new strand is produced from an old strand and two complete DNA molecules remain

II.  How proteins are made

       A.  The transfer of genetic information

    1. Dna is used as a blueprint to make a similar nucleic acid called RNA
    2. Rna then is used to direct the production of a protein
    3. Gene expression is the productionof proteins from the DNA
    4. Gene expression takes place in two steps, Transcription and translation
    5. Three different kinds of RNA are used to code for amino acids which accumulate to make proteins
    6. DNA cannot leave the nucleus os messengers (RNA) have to carry the code to the sites of proteins synthesis
    7. RNA is similar to DNA with three exceptions,
    1. RNA uses the sugar Ribose, instead of Deoxyribose
    2. RNA is single stranded, DNA is double stranded
    3. RNA uses the base Uracil instead of the base Thymine\

            8.  RNA occurs in three different forms

    1. Messenger RNA carries the code from the Nucleus to the Ribosome
    2. Transfer RNA carries specific amino acids to the sites of proteins synthesis
    3. Ribosomal RNA actually make up the ribosomes which ahave two parts. A larger subunit and a small subunit.

         B.  How DNA makes RNA

    1. A section of the DNA opens up when RNA polymerase binds to the promoter region
    2. The DNA begins to unwind, exposing the interior of the DNA molecule
    3. RNA polymerase moves along the DNA molecule, placing complimentary bases to the DNA in a chain
    4. The process will continues until a stiop sign called a stop codon is reached
    5. The newly transcribed RNA molecule leaves the nucleus through a nuclear pore and into the cytoplasm it goes.
    6. Once the RNA polymerase stops transcription, it releases the DNA and it winds back up

        C.  The genetic code

    1. The genetic code is read in sequence of three bases at a time called a codon
    2. The codon of the RNA molecule is the Code for the Protein
    3. Amino acids need to be chained together to make a protein
    4. The codons ultimately code for Amino acids.
    5. The transfer RNA has a match for the code on one side (anticodon) and attached to the top of the Transfer RNA is an amino acid
    6. U,C, G, and A are the bases found in mRNA
    7. There are 64 different codons that can be made from these 4 letters
    8. There are only 20 different amino acids so some tRNA will carry the same amino acids as other tRNA
    9. At the beginning of each mRNA is a codon that codes for an amino acid,
    10. As the mRNS is locked into place, The codon on the mRNA is read and the corresponding anticodon is located
    11. The anticodon is aligned with the codon at the ribosome and the RNA molecule will be advanced one spot
    12. The Next codon is read, the appropriate anitcodon is found and brought to the ribosome
    13. As the second codon and anticodon are lined up, a peptide bond forms between the first and second amino acid forming a peptide chain
    14. This goes on and on until a stop codon is found, at which point there is not amino acid for and the synthesis of a protein is terminated
    15. From the time the mRNA is locked into a ribosome, the process of transcription has taken place

III.  Regulating Gene Expression

       A.  Switching genes on and off

    1. Depending on the needs of the cell, a gene can be turned on or off as needed
    2. Those that are turned off are done so until the protein that they code for are needed
    3. Genes are turned off because a special protein called a repressor protein is attached to the front of the particular gene
    4. Another protein called an inducer protein must bind to the repressor protein to remove it from the gene
    5. At this point the DNA can be expressed (transcription and translation can then occur)

        B.   Architecture of the gene