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.DNA Replication Activity.

Part 1:

Use the nucleotide models you cut out to simulate replication. Follow the instructions below and use the picture as a guide. Learn the underlined terms in each numbered items. The numbered items actually explain the terms and what happens during replication. The lettered items are instructions for manipulating your model pieces. Manipulating the model pieces will help you visualize and understand the replication process described by the numbered items.

Part 2:

In Part 1 of this activity, you read and reread the handout describing the process of replication. You also manipulated your nucleotide models to simulate replication in an effort to gain an in depth understanding of the process. In Part 2 of this activity, you will benefit from the amount of effort you used to learn about replication.

Take your nucleotide models and run them through the process of replication. As you do this, describe each step of the process in your own words. Use the 18 underlined words in your explanation. Underline these words as you explain them for credit. Also cut out the pictures you were given and place them appropriately in your explanation. Also label the different items in the pictures. Grades will be based on effort, accuracy, and completeness.


.DNA Replication Activity.


DNA, the molecule that holds genetic information, makes an exact copy of itself whenever a cell divides. This copying process is called replication. Replication occurs during interphase of the cell cycle and two identical copies of every chromosome must be produced before mitosis, meiosis, or binary fission can take place. Replication occurs inside the nuclear membrane of a cells nucleus. In this activity, it's up to you to use the process of replication and make the copy.

Materials: Cut out paper nucleotide models.
24 nucleotide models separated into two sets. Each set must have three nucleotide models for each of the four bases. Each set must have: three nucleotide models with adenine as the base, three nucleotide models with thymine as the base, three nucleotide models with cytosine as the base, and three nucleotide models with guanine as the base.

Procedure:
1. Nucleotides are the subunit molecules that make up DNA. The sugars and phosphates on the models will make up the sides of the model DNA molecule. The bases between the sides must consist of complementary pairs. In other words, adenine is paired with thymine and cytosine is paired with guanine. This model strand of DNA will represent an original strand of DNA before replication. A. Take one set of models and arrange the nucleotides into a double nucleotide strand of DNA.

2. Replication starts at thousands of places called origins along a chromosome. The two strands that make up DNA are separated at an origin. The molecule that separates or unzips the two strands is called helicase. Helicase is an enzyme that breaks the hydrogen bonds between complementary bases. Two helicase molecules move in opposite directions at each origin. The two strands make a “Y” shaped region called a replication fork where they are separated. Separate one end of the model strand of DNA into a replication fork. B. Make the fork by sliding first nucleotides apart about 4.5 inches and slide the second nucleotides apart about half as much.

3. As the replication fork, made by the helicase enzyme, moves down the strand of DNA, the bases on its nucleotides are exposed. Free nucleotides in the cell's nucleus are paired in a complementary manner to these exposed bases. Molecule called DNA polymerase moves down each original side strand of DNA connecting these bases into a new side-strand of DNA. DNA polymerase is an enzyme that helps form the covalent bonds between the sugars and phosphates of adjacent nucleotides on the new growing side-strand of DNA.
C. Look for the side of the fork that has a phosphate molecule at the end. Place a nucleotide with a complementary base next to the nucleotide you just found.

4. The original DNA side-strand to which you just added a nucleotide is called the leading strand. A new DNA side-strand starts with the nucleotide you just placed. This new DNA strand “grows” one nucleotide at a time following the helicase and opening replication fork. DNA polymerase also follows the helicase bonding the sugars and phosphates of each nucleotide on the growing strand. Because the growth of the leading stand follows the opening replication fork, it is added as one continuous piece. D. Open the replication fork on your model pieces one more nucleotide. Add a nucleotide with a complementary base. Repeat this two more times.

5. The original DNA side-strand to which there are no nucleotides added is called the lagging strand. DNA polymerase can only move down DNA in one direction, so nucleotides on the lagging strand are added opposite to the direction of nucleotides being added to the leading strand. In other words, nucleotides are added to the lagging strand in the direction away from the replication fork and movement of the helicase enzyme. Because DNA polymerase can only move down the lagging strand away form the replication fork, the new growing side-strand is added in fragments/pieces. E. Add complementary nucleotides to the bases exposed on the lagging strand starting at the replication fork and moving away from it.

6. At this point, both new side-strands of DNA are growing on the leading and lagging strands of the original double strand of DNA. When finished, the leading and lagging strands will be two identical, separate, double strands of DNA. Each of these double strands will have one new and one old strand of DNA. Because of this replication is called semi-conservative. F. Open the replication fork the rest of the way one base at a time. Place complementary nucleotides on the exposed bases of the leading strand as you open the fork. G. Place a complementary nucleotide on the exposed base of the lagging strand farthest away from the bases already already on the lagging strand. Starting next to this nucleotide, add complementary nucleotides to the lagging strand until it is complete. A DNA polymerase will move down the lagging strand bonding the sugars and phosphates of nucleotides being added. DNA polymerase can't bond the fragments of the new strand that has been added to the lagging strand. Another enzyme called DNA ligase connects the new pieces that will make up the new strand that complements the lagging strand. Replication is now complete resulting in two identical double strands of DNA.

Visual Guide:

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Nucleotide Paper Models: Two sets are needed to do replication.

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