{"id":149,"date":"2017-02-04T22:31:11","date_gmt":"2017-02-05T05:31:11","guid":{"rendered":"https:\/\/blogs.ubc.ca\/mrpletsch\/?p=149"},"modified":"2019-09-03T10:54:17","modified_gmt":"2019-09-03T17:54:17","slug":"2-7-dna-replication-transcription-translation","status":"publish","type":"post","link":"https:\/\/blogs.ubc.ca\/mrpletsch\/2017\/02\/04\/2-7-dna-replication-transcription-translation\/","title":{"rendered":"2.7 DNA Replication, Transcription, Translation"},"content":{"rendered":"

Essential Idea:<\/strong> Genetic information in DNA can be accurately copied and can be translated to make the proteins needed by the cell.<\/p>\n

DNA structure and replication crash course<\/a><\/p>\n\n

Transcription and Translation crash course<\/a><\/p>\n

Protein Synthesis slides (Bio 115)<\/a><\/p>\n\n

DNA Replication – Basics
\n<\/strong><\/h3>\n

2.7.U1 -The replication of DNA is semi-conservative and depends on complementary base pairing.<\/strong><\/p>\n

\"\"
Figure 1: DNA complementary base pairing<\/figcaption><\/figure>\n

Two DNA strands are held together by hydrogen bonding between complementary base pairs.<\/u><\/p>\n

    \n
  • Adenine is always matched with Thymine with two hydrogen bonds<\/li>\n
  • Guanine is always matched with Cytosine with three hydrogen bond<\/li>\n
  • This is due to the molecular structure of the base pairs.<\/li>\n
  • Base paring ensures two identical DNA strands are formed after replication is complete<\/li>\n
  • The parental strand acts as a template and therefore each replicated strand is identical and each daughter cell has the same DNA.<\/li>\n<\/ul>\n
    \"\"
    Figure 2: DNA replication outline<\/figcaption><\/figure>\n

    Due to this, DNA replication is semi-conservative<\/strong> \u2013 or each new DNA strand has one parental strand (template) and one newly synthesized strand.<\/strong><\/p>\n

    \"\"
    Figure 3: Semi-conservative DNA replication<\/figcaption><\/figure>\n

    How do we know DNA replication is semi-conservative?<\/b><\/p>\n

      \n
    • Originally, there were three proposed methods:<\/u><\/li>\n
    • 1) Conservative<\/b> \u2013 parental strand rejoins after replication<\/li>\n
    • 2) Dispersive<\/b> \u2013 parental DNA double helix is broken into segments that act as templates<\/li>\n
    • 3) Semi<\/b>-conservative <\/b>– two parental DNA strands separate and each of those strands then serves as a template for the synthesis of a new DNA strand.<\/li>\n<\/ul>\n
      \"\"
      Figure 5: The three proposed methods of DNA replication<\/figcaption><\/figure>\n

      In 1957, Meselson and Stahl conducted an experiment providing evidence for semi-conservative replication.<\/strong><\/p>\n

      2.7.A2 – Analysis of Meselson and Stahl\u2019s results to obtain support for the theory of semi-conservative replication of DNA.<\/strong><\/p>\n

      Meselson and Stahl experiment:<\/h5>\n
      \n
      “They began by growing E. coli in medium, or nutrient broth, containing a “heavy” isotope of nitrogen, 15N<\/span><\/span>. (An isotope<\/strong> is just a version of an element that differs from other versions by the number of neutrons in its nucleus.) When grown on medium containing heavy 15N<\/span><\/span>, the bacteria took up the nitrogen and used it to synthesize new biological molecules, including DNA.<\/em><\/div>\n<\/div>\n
      \n
      After many generations growing in the 15N<\/span><\/span> medium, the nitrogenous bases of the bacteria’s DNA were all labeled with heavy 15N<\/span><\/span>. Then, the bacteria were switched to medium containing a “light” 14N<\/span><\/span> isotope and allowed to grow for several generations. DNA made after the switch would have to be made up of 14N<\/span><\/span>, as this would have been the only nitrogen available for DNA synthesis.<\/em><\/div>\n<\/div>\n
      \n
      Meselson and Stahl knew how often E. coli cells divided, so they were able to collect small samples in each generation and extract and purify the DNA. They then measured the density of the DNA (and, indirectly, its 15N <\/span><\/span>and 14N<\/span><\/span> content) using density gradient centrifugation<\/strong>.<\/em><\/div>\n<\/div>\n
      \n
      This method separates molecules such as DNA into bands by spinning them at high speeds in the presence of another molecule, such as cesium chloride, that forms a density gradient from the top to the bottom of the spinning tube. Density gradient centrifugation allows very small differences\u2014like those between 15N<\/span><\/span> and 14N<\/span><\/span>, N-labeled DNA\u2014to be detected.”<\/em><\/div>\n
      <\/div>\n
      <\/div>\n
      Quoted from https:\/\/www.khanacademy.org\/science\/biology\/dna-as-the-genetic-material\/dna-replication\/a\/mode-of-dna-replication-meselson-stahl-experiment<\/em><\/div>\n
      <\/div>\n<\/div>\n
      <\/div>\n
      So,<\/div>\n
      \n
        \n
      • DNA is semi-conservative in terms of replication.<\/li>\n
      • Using the parental DNA strand as a template, two identical strands of DNA are produced.<\/li>\n
      • But, in order for base pairing to occur, we need to unzip to DNA.<\/li>\n<\/ul>\n

         <\/p>\n<\/div>\n