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Structure and Duplication of DNA

  • Memorize the names of the six components of a DNA Molecule
  • Learn the relationships between the nitrogen bases in a DNA Molecule.
  • Learn the arrangement of sugar and phosphate units in a DNA Molecule
  • Observe that the arrangement of bases along a DNA molecule is the genetic code
  • Observe how one strand of DNA becomes two strands. (DNA Replication)
  • Be able to assemble a molecule of DNA using a model
  • Be able to show DNA replication using a model.
  • Be able to explain the “zipper theory” of the DNA molecule.
  • Be able to identify the following parts of a DNA molecule:
the nitrogen bases of adenine, cytosine, guanine, and thymine; Sugar units, and phosphate units.
  • Visualize that DNA is made up of nucleotides which are units consisting of a phosphate, a sugar, and a base.

Procedure: Print the three pages of DNA model pieces.

DNA Structure:
First, cut out the page labeled Model 12_1 . Assemble these model DNA pieces so they look like the sides of a ladder. While you are cutting, note and memorize the labels associated with the various paper DNA pieces. The phosphates pieces will go between the sugar pieces to made up the “side chains” of the DNA molecule. Next, cut out the page labeled Model 12_2. Use these base pieces to assemble the steps or rungs of the ladder. The shapes of the model pieces will guide their assembly. Learn which base pairs work together to make the rungs of the ladder.

Concept Check:
How many different pairs of nitrogen bases make up the “rungs” of the DNA “ladder”?
What bases make up the possible nitrogen base pairs?
Do the nitrogen base pairs bond with the sugar or phosphate units that form the sides of the DNA molecule?
How many different ways can the base pairs be placed in the six available positions of this model?
The order of base pairs in the DNA molecules is the genetic code. A gene is a section DNA that codes for a protein. The human genome is estimated to be about 3 billion base pairs long and to contain 20,000 to 25,000 distinct genes.

Procedure Continued:

DNA Replication
Cut out the items (three piece units each) on the page labeled 12_3. These three piece units are called nucleotides. Nucleotides are the structural units of DNA. Nucleotides are free floating in the cells and provide building blocks as the DNA makes an exact copy of itself.
(Nucleotide - )
Watch the animation to seen how two copies of DNA are produced from the original.
First, assemble a single strand of DNA using the sugars, phosphate, and base pieces that you cut out of the pages labeled Model 12-1 and 12-2.
Second, add the nucleotide pieces cut out of the page labeled model 12-3 to the above strand of DNA.
Move the parts of your assembled DNA model, and your nucleotides through the positions seen in the animation of DNA replication. From this experience, determine the sequence of events that occur as a molecule of DNA replicates.

DNA Replication Animation

2nd Animation Using Photos

Alternative Animation:

Concept Check:
What is the role of the nucleotide units as the DNA molecule separates?
What is a nucleotide unit made of?
How many different nucleotides are there in DNA?
What differentiates on DNA nucleotide from another?
What process was modeled when you changed you original DNA molecule into two DNA molecules?
How do the two DNA molecules that you produced using this process compare?
What structural characteristics of the DNA molecule would seem to minimize errors produced by damage?
Using one word, can you describe the way in which the DNA molecule separates as it is replicating?
Remember that the process of replication precedes mitosis and meiosis.

Extra Credit: Make your own animation of this process and provide an explanation.