Exam 3 Bio 200 Notes

Last update by mayur on 03/28/2014
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Explain why researchers originally thought protein was the genetic material

. It boils down to variety: it was known that proteins were made from 20 different amino acids, while DNA is made of only four different bases. It kinda makes sense, then, that proteins could code for MUCH greater variety in their amino acid sequence than DNA could in its nucleotide sequence.

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  • tsrewop
    Frederick Griffith experiments
    transforming principle...mice injected with dead S and live R bacteria died...so something had to transform from the s bacteria
  • tsrewop
    Hershey and chase experiments
    virus phages and bacteria...concluding dna moved into bacteria...not protein
  • tsrewop
    avery, mccarthy, macleod experiments
    Oswald Avery was in the Rockefeller institute, and there he re-performed Griffith's experiments. He took out things like DNA, protein, and RNA from the heat-killed harmful bacteria and injected each into the living harmless bacteria until he found which one caused the harmless to transform into harmful. He found that DNA caused it, so DNA transfers such genetic information. 
  • tsrewop
    Explain how Watson and Crick deduced the structure of DNA and describe the evidence
    they used. Explain the significance of the research of Rosalind Franklin.
    Watson and Crick built a 3D model of DNA.

    Franklin used X-rays and found a sort of double helix pattern in DNA.
  • tsrewop
    Chargaff experiments
     Chargaff... He experimented with molecular diversity of DNA and the multitude of combinations of the nucleotides; A, T, C and G. This diversity and the diversity among living things supported DNA as the genetic material
  • tsrewop
    Describe the structure of DNA. Explain the base-pairing rule and describe its significance.
    Deoxy-ribonucleic Acid, DNA as we know it to be, has a double helical structure and is made up of small molecules called nucleotides. 

    (DNA can in other words be referred to as a nucleotide polymer.)Each nucleotide comprises a 5-carbon sugar, a nitrogenous base and a phosphate group.

    These are joined together to form a ''twisted-ladder''. One complete turn of the twisted ladder (i.e the double helical structure), which could be likened to the pitch of a screw, has an approx. length of 3.4nm and a 2nm width.
    This is achieved chiefly by the complementarily of the base pairing that occurs with the bases in DNA.
    (Remember, Guanine always bonds to Cytosine with 3 hydrogen bonds and Adenine to Thymine with two hydrogen bonds!). 
    In RNA however, the base thymine is replaced with Uracil. 
    This means that the base that is complementary to Adenine on a DNA strand would be Uracil on the RNA strand. 
    The main significance of base pairing is to enable the maintenance of the gene pool within a species. 
    You will greatly appreciate that the DNA sequence that codes for a certain protein must be constant so as to make sure that it codes for that same protein when it is translated. 
  • tsrewop
    Describe the semiconservative model of replication and the significance of the experiments
    of Matthew Meselson and Franklin Stahl.
    The Meselson-Stahl experiment by Matthew Meselson and Franklin Stahl showed that DNA replication was semiconservative.

    Semiconservative replication means that the DNA double helix strand, on replication, produces two double-stranded DNA helices. Each one has an original DNA helix strand and one new synthenized DNA helix strand.

    The Meselson-Stahl Experiment
    To begin with, to be able to tell the old and new DNA apart, Meselson and Stahl grew several generations of Echerichia coli bacteria in two different mediums, one in the "heavy" nitrogen isotope 15N and the other in the "light" nitrogen isotope 14N. So, it turned out, that one bacterial culture contained the heavy form of nitrogen and the other contained the light form of nitrogen.

    Then, taking samples of each and extracting DNA into solution, the scientists mixed the two DNA solutions together and added the mix to a CsCl (cesium chloride) solution of the same density. This mix was then processed at high speed in an ultracentrifuge. The result was a mixture separated by density—the "heavy" mix was denser than the "light" mix and so the "heavy" mix sank to the bottom and the "light" mix moved up. Thus it was possible to tell the two apart.

    Next, the scientists grew several generations of E.coli in 'heavy' nitrogen medium, and extracted a DNA sample from these bacterial cells. They called this sample "generation zero" and prepared it for centrifugation. The result showed that the DNA in generation zero had a heavier density, that is was in the "heavy" form.

    The scientists then transferred the E.coli bacterial cells to the "light" nitrogen medium and allowed it to grow in that. They took samples from this every 20 minutes and processed these samples too in an ultracentrifuge.

    The first result, after one generation, showed that the DNA had an intermediate density rather than heavy or light. This ruled out conservative replication, as, in that case, the result wouldn't have shown intermediate density, but rather equal amounts of heavy and light DNA. On the other hand, intermediate density would be possible with both semiconservative and dispersive replication.

    The second result, after two generations, showed that one part of the DNA had intermediate density and the other part had light density. This ruled out dispersive replication as in that case the DNA distribution would have been same between the strands and the resulting density would have been lower than the intermediate one.

    The third result, after several more generations, showed that now a larger portion of the DNA had light density, synthenized from the first and second generations, and a smaller portion of DNA had intermediate density, sythesized from the heavy and light DNA. This proved the semiconservative hypothesis and was a major step in developmental biology research

  • tsrewop
    Describe the process of DNA replication, including the role of the origins of replication and
    replication forks.
    The replication fork is a structure that forms within the nucleus during DNA replication. It is created by helicases, which break the hydrogen bonds holding the two DNA strands together. The resulting structure has two branching "prongs", each one made up of a single strand of DNA. These two strands serve as the template for the leading and lagging strands which will be created as DNA polymerase matches complementary nucleotides to the templates; The templates may be properly referred to as the leading strand template and the lagging strand template.r a cell to divide, it must first replicate its DNA.This process is initiated at particular points within the DNA, known as "origins" which are targeted by proteins that separate the two strands and initiate DNA synthesis...Origins contain DNA sequences recognized by replication initiator proteins. These initiator proteins recruit other proteins to separate the two strands and initiate replication forks.

    DNA synthesis begins at specific locations in the genome, called "origins", where the two strands of DNA are separated. 

    RNA primers attach to single stranded DNA and DNA polymerase extends from the primers to form new strands of DNA, adding nucleotides matched to the template strand. 

    The unwinding of DNA and synthesis of new strands forms a replication fork. 

    In addition to DNA polymerase, a number of enzymes are associated with the fork and assist in the initiation and continuation of DNA synthesis. 

    DNA polymerase adds nucleotides to the 3' end of a strand of DNA. 

    If a mismatch is accidentally incorporated, the polymerase is inhibited from further extension. Proofreading removes the mismatched nucleotide and extension continues.

    DNA polymerases are a family of enzymes critical for all forms of DNA replication. A DNA polymerase synthesizes a new strand of DNA by extending the 3' end of an existing nucleotide chain, adding new nucleotides matched to the template strand one at a time. 

    Some DNA polymerases may also have some proofreading ability, removing nucleotides from the end of a strand in order to remove any mismatched bases. 

    DNA polymerases are generally extremely accurate, making less than one error for every million nucleotides added.

  • tsrewop
    Explain the role of DNA polymerases in replication.

    Catalyzes the transcription of DNA

    DNA polymerases exist as dimers associated with the other necessary proteins at the replication fork and this representation is identified as the replisome. The template for the lagging strand is temporarily looped through the replisome such that the DNA polymerases are moving along both strands in the 3'---->5' direction simultaneously for short distances, up to the distance of an Okazaki fragment.

    As the replication forks progresses along the template strands, the newly synthesized daughter strands and parental template strands reform a DNA double helix. Hence it is explicit that that only a small stretch of the template duplex is single-stranded at any given time.

    The progression of the replication fork requires that the DNA ahead of the fork be continuously unwound. Since the eukaryotic chromosomal DNA is attached to a protein scaffold the progressive movement of the replication fork thus intruding severe torsional stress into the duplex ahead of the fork.

  • tsrewop
    Explain what energy source drives the polymerization of DNA.
    splitting pyrophosphate from the incoming nucleotide and the eventual splitting of pyrophosphate to 2 phosphate molecules by water
  • tsrewop
    Distinguish between the leading strand and the lagging strand.
    The Leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction. Also the Leading strand is synthesized continously, whereas the lagging strand is synthesized in short fragments that are ultimately stitched together(-okazaki fragments)
Exam 3 Bio 200 Notes
Exam 3 Bio 200 Notes
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Genetics is what chapters this exam basically covers--These flashcards are for personal use only and a compilation of information from my own personal knowledge, the web, and my textbook. I am only using these for studying. They will be taken off at the e
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