lecture 3-1

• Deoxyribonucleic acid is genetic material that encodes all the traits that make up a species and is inherited from one generation to the next.
• DNA contains a deoxyribose, nitrogen base, and a phosphate group. One unit that has all 3 parts is a nucleotide.
• Adenine and guanine are purines while cytosine and thymine are pyrmidines.
• Fill in the rest

  A) Adenine

  B) Thymine

  C) Guanine

  D) Cytosine

  
• Watson and Crick discovered DNA replication
• DNA replication is a semiconservative process, meaning that each new DNA molecule contains one new strand and one old strand from the parent molecule.
• The steps of DNA replication are

  1. Unwinding of the strands (helicase)
  2. Separation of the strands (single-stranded binding proteins)
  3. Straightening of the strands (topoisomerase)
  4. Addition of primers (primase)
  5. Addition of new nucleotides from 5' to 3' (DNA polymerase III)
  6. Replacement of RNA primers (DNA polymerase I)
  7. ligation of Okazaki fragments if it's a lagging strand (ligase)
• Label the replisome

  A) helicase

  B) polymerase

  C) primase

  D) SSB

  E) RNA Primer

  
• What can be found in the replisome?

  DNA polymerase, helicase, primase, SSB proteins, and RNA primers
• Where does DNA replication start?

  Origin of replication.
• Label this replication bubble

  A) origin of replication

  B) primer

  C) lagging

  D) lagging

  E) leading

  F) leading

  
• Why are RNA primers necessary to initiate DNA replication?

  Because DNA cannot be synthesized de novo.
• Okazaki fragments are found on the lagging strand and are joined together by ligase
• Helicase: Unwinds the DNA molecule
• Topoisomerase: Relieves strain in the DNA molecule
• Primase: Adds a primer to give a 3’ end
• DNA polymerase III: Adds nucleotides to both strands
• DNA polymerase I: Converts primers to DNA on both strands
• Ligase: Joins up all Okazaki fragments
• The end replication problem is caused by the inability of DNA polymerase I to replace the very last primer site on the lagging strand, since there is no 3' site for the enzyme to attach to. This leads to the DNA molecule shortening every cycle of replication and can result in cell death.
• A telomere is initially added first as an RNA strand by telomerase, then changed to DNA and it extends each end of the DNA molecule. It is a region of non-coding DNA.
• Highest amount of the telomerase enzyme are found in gametes and in newborn babies. They are also longer in cancer cells and in people who exercise daily.
• Mis-match repair is the process of repairing DNA whose base pairings are incorrect. The incorrect DNA is cut out by a nuclease enzyme, filled in with the correct nucleotides by DNA polymerase, and is ligated by DNA ligase.
• DNA can be damaged by UV light, X-rays, cigarette smoke, and mutagenic agents. This damage can lead to cancer.