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DNA-Replication-LAB

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					                                                   DNA REPLICATION LAB

Name: ___________________________                                          Period: ________                 Date: ________


                                                   DNA REPLICATION LAB
Background:
          DNA is composed of a twisted double helix, or ladder, with the sides composed of alternating 5-carbon sugars and phosphate
units. The rungs or steps to the ladder are the four nitrogen bases - adenine (A), thymine (T), guanine (G), and cytosine (C).
          A nucleotide is a three part unit composed of sugar, phosphate, and one nitrogen base. Nucleotides linked together make the two
sides of the DNA double helix.
          DNA replication is a process that occurs in the nucleus of all cells just before cell division. In order for replication to occur, with
the aid of an enzyme (DNAase) DNA must first untwist, unzip, and expose its nitrogen bases. Unbound nucleotides found floating in the
nucleus find the correct base on the exposed DNA molecule and join with it with the help of an enzyme (DNA polymerase). Once the
base pairing is complete, the 2 new DNA molecules then twist back into a spiral. Remember the base pairing rule of A-T and C-G. This
process forms two identical strands of DNA - one for each new cell.

Purpose:
         To construct a DNA molecule and show the steps of DNA replication.

Procedure:
         1. Using the pieces supplied, make a DNA molecule with at least 6-8 rungs. Page 144 of your text will help you with the
configuration of each of the molecules involved. Your bases do not need to be the same as those in the book, but you must follow the
base pairing rule. Have your teacher check your DNA molecule and then answer questions #1-11.
         2. Unzip the DNA molecule between the bases. Using the extra, loose molecules of the nucleotides, match them to the proper
exposed bases on the original DNA strands. If you do this correctly, the result should be two identical DNA strands. Have your teacher
check the strands and then answer questions #12-18.

Observations:
     1.    What are the three components of a nucleotide?


         2.       The nitrogen base adenine (A) bonds with base?


         3. The nitrogen base cytosine (C) bonds with which base?


         4. If the order of the nucleotides in your model had the base sequence of A-C-C-G-T-A-T-C-G,
                 what would be the sequence on the opposite side of the DNA molecule?



         5. Why could the sequence in (#4) be the only correct sequence?



         6. What terms are used to describe the shape of the DNA molecule?




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                                            DNA REPLICATION LAB

       7. How many sides are found on your DNA molecule?


       8. Which molecule on the sides of your DNA model is attached to the nitrogen bases?



       9. With all of the pieces of DNA on your table top, which cell organelle could your table represent?



       10. How many DNA molecules result from the steps of replication you worked out on the table top?


       11. What is a synonym for "replication"?


       12. Reviewing the steps you went through during replication, which bond do you think is stronger among
       the different units of a DNA nucleotide: the bond between the two nitrogen bases or the bond between the
       sugars and phosphates? Why?




       13. What substance did your hand represent when you unzipped the two halves of the DNA molecule?



       14. When does replication occur in our bodies?



Use your notes, the information in this lab, and the diagram on page 145 of your textbook to draw the main steps
of DNA replication in the spaces below. Be sure to label your molecules.


 Step 1 - DNA enzymes cause the molecule to untwist and unzip thus exposing the nitrogen bases.




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                                             DNA REPLICATION LAB

Step 2 - Nucleotides, floating freely in the nucleus, bond (with the help of enzymes) to the exposed bases




Step 3 - Once bonding is complete the two strands (with the help of enzymes) retwist .




      15. Why is replication important to our bodies?




      16. Observe the end product of replication on your lab table; are the two copies of DNA different or
             identical?




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                                      DNA REPLICATION LAB

WORD RELATIONSHIPS: Circle the one word that does not belong and in the space provided explain why it
does not belong with the other words.

      18. deoxyribose,    double helix,        DNA,                ribosome

      19. Why?


      20. thymine,        hydrogen bonds,      guanine,            adenine

      21. Why?


      22. cytosine,       5-carbon sugar,      nitrogen bases,      phosphates

      23. Why?


      24. Watson,         Franklin,            Nobel prize,         Crick

      25. Why?




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