Student Exploration: Building DNA
Vocabulary: double helix, DNA, enzyme, 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.
- Look at the DNA molecule shown at right. What does it look like?
This shape is called a double helix.
- 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.)
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.
- What are the two DNA components shown in the Gizmo?
- 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).
Build a DNA molecule
Get the Gizmo ready:
· If necessary, click Reset to start the building process.
Question: What is the structure of DNA?
- 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 side of the DNA molecule and the right-hand side.
- Take a picture: Click the camera () to take a snapshot of your DNA molecule. Right-click the image and select Copy Image. Paste the image into the space below, labelled “Original DNA molecule.”
Original DNA molecule.
Left side Right side
- Explain: Describe the structure of the DNA molecule you made.
- What makes up the sides of the DNA molecule? ________________
- What makes up the “rungs” of the DNA molecule? _______________
- 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 __________
Get the Gizmo ready:
· Be sure the hint reads: “The DNA molecule is complete.” If not, click Reset and build a new DNA molecule.
Question: How does DNA make a copy of itself?
- Observe: An enzyme is a protein that facilitates certain cell processes. Click Release enzyme to release DNA helicase. What does this enzyme do to the DNA molecule?
- Observe: Click Release enzyme to release DNA polymerase.
- Notice that two groups of Nucleotides appear on the right. What are the three parts of a nucleotide? __________, __________, __________
- Drag one of the nucleotides to a corresponding nitrogenous base on one of the two strands. What is the role of DNA polymerase in this process? __________________
- Build: Complete the two molecules of DNA by dragging nucleotides to their corresponding locations. When you have finished, compare the two completed daughter DNA molecules.
What do you notice about the two molecules? _____________
- Take a picture: Click the camera to take a snapshot of the DNA molecules, and paste the image below.
Daughter DNA molecules
How do these molecules compare to the original? _____________
- Think and discuss: Why is DNA replication such an important process? Read p.352-353