DNA: STRUCTURE AND REPLICATION (Filmstrip)

Structure of DNA

  1. DNA stands for _____________________________________________

  2. DNA is an unusual molecule in that it:
    a) __________________________________________________________________
    b) __________________________________________________________________

  3. DNA is the primary material found in ____________________________________ (evidence suggests that a chromosome is a single coiled molecule of DNA)

  4. Humans possess (in their body/somatic cells) ______________ chromosomes. We inherit _______ chromosomes from our mother and ______ from our father.

  5. In eukaryotic cells, DNA molecules (chromosomes) are found in the ___________________.

  6. The 3-dimensional structure of DNA was discovered by ____________________ and ___________________.

  7. The shape of the DNA molecule is best described as a ____________________ ____________________ with ____________________ bonded to the ____________________.

  8. The building blocks of DNA are units called ______________________________. A nucleotide consists of 3 parts:
    a) ______________________________
    b) ______________________________
    c) ______________________________

  9. Sketch and label a nucleotide below:










  10. There are 4 kinds of nucleotides in DNA:
    a) _________________________
    b) _________________________
    c) _________________________
    d) _________________________

  11. PURINE nucleotides include ____________________ and ____________________. PYRIMIDINE nucleotides include ____________________ and ____________________.

  12. Adenine always bonds with ____________________ and cytosine always bonds with ____________________. This is called "complementary base pairing".

  13. Sketch and label an unwound DNA fragment below.









  14. Sketch the chemical structure of the phosphate group.






  15. Sketch the chemical structure of deoxyribose sugar.






  16. How many rings are present in adenine and guanine (purines)? _______
    How many rings are present in cytosine and thymine (pyrimidines)? ______

Replication of DNA (occurs during Interphase)

  1. Are the bonds between complementary bases weak or strong? _______________. What kind of chemical bond holds the strands together at the bases? ________________ bonds.

  2. DNA separates (unzips) between the ____________________ and the molecule may also unwind (ie. the _____________________ bonds are broken). The OLD strands are now separated. This step requires the enzyme ____________________.

  3. New ____________________ (which are floating around in the nucleus) are matched and bonded to complementary bases on the outer OLD strands to form inner NEW strands. This is called "complementary _____________ ___________________". This step requires the enzyme _________ ____________________ because new polymers (long strands of molecules) are being produced.

  4. Then the "backbone" (which consists of ____________________ and ____________________ molecules) is "zipped up" by the enzyme ____________________. In this step, each nucleotide in a new strand is joined to the one above and below it at the phosphates and sugars.

  5. Thus, ______ DNA molecules are produced from the original molecule. The DNA molecules make up the chromosomes which stay joined to eachother due to a ___________________________.

  6. The DNA molecules produced by DNA replication are ____________________ to each other.

  7. The replicated DNA molecules (chromosomes) are now ready to go into ______________________