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  • Topic: DNA, DNA replication, RNA
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  • Published : January 1, 2013
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Name: ______________________________________Date: ________________________

Student Exploration: Building DNA

Vocabulary: double helix, DNA, enzyme, lagging strand, leading strand, mutation, nitrogenous base, nucleoside, nucleotide, replication

Prior Knowledge Questions (Do these BEFORE using the Gizmo.) DNA is an incredible molecule that forms the basis of life on Earth. DNA molecules contain instructions for building every living organism on Earth, from the tiniest bacterium to a massive blue whale. DNA also has the ability to replicate, or make copies of itself. This allows living things to grow and reproduce.

1. Look at the DNA molecule shown at right. What does it look like?


This shape is called a double helix.

2. Based on this picture, how do you think a DNA molecule makes a copy of itself? (Hint: Look at the bottom two “rungs” of the ladder.)



Gizmo Warm-up
The Building DNA Gizmo™ allows you to construct a DNA molecule and go through the process of DNA replication. Examine the components that make up a DNA molecule.

1. What are the two DNA components shown in the Gizmo?


2. A nucleoside has two parts: a pentagonal sugar (deoxyribose) and a nitrogenous base (in color). When a nucleoside is joined to a phosphate, it is called a nucleotide.

How many different nitrogenous bases do you see? ________________________________

Note: The names of these nitrogenous bases are adenine (red), cytosine (yellow), guanine (blue), and thymine (green).

|Activity A: |Get the Gizmo ready: |[pic] | | |If necessary, click Reset to start the building process. | | |Build a DNA molecule | | |

Question: What is the structure of DNA?
2. Build: Follow the steps given in the Gizmo to construct a molecule of DNA. (Note: For simplicity, this DNA molecule is shown in two dimensions, without the twist.)

Stop when the hint reads: “The DNA molecule is complete.” In the spaces at right, list the sequence of nitrogenous bases on the left-hand strand, called the leading strand, and the right-hand strand, called the lagging strand.

3. Take a picture: Click the camera ([pic]) at upper right to take a snapshot of your DNA molecule. Open a blank word-processing document, and select paste. Label this image “Original DNA molecule.”

Leading strandLagging strand









4. Explain: Describe the structure of the DNA molecule you made.

A. What makes up the sides of the DNA molecule? ____________________________

B. What makes up the “rungs” of the DNA molecule? ___________________________

5. Fill in: Write the name of the nitrogenous base that joins to each of the bases below:

Adenine (A) joins to _______________Thymine (T) joins to _______________

Cytosine (C) joins to _______________Guanine (G) joins to _______________

6. Practice: The leading strand of a DNA molecule is shown. Draw a complementary lagging strand on the right side of this molecule.

7. Challenge: This DNA strand consists of eight pairs of nitrogenous bases. How many different sequences of eight bases can you make? Explain how you...
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