Student Exploration: Building DNA (ANSWER KEY)

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 have instructions for building every living organism on Earth, from the tiniest bacterium to a massive blue whale. DNA also can 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? The shape to the right looks like a spiral staircase.
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.) I think that the DNA molecule would split down the middle and copy itself.

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.
What are the two DNA components shown in the Gizmo? 
A nucleoside has two parts: a pentagonal sugar (deoxyribose) and a (in color). When a nucleoside is joined to a phosphate, it is called a .
How many different nitrogenous bases do you see? 4
Note: The names of these nitrogenous bases are adenine (red), cytosine (yellow), guanine (blue), and thymine (green).


Activity A:

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 strand, called the , and the right-hand strand, called the .
Leading strand      Lagging strand

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 

Practice: The leading strand of a DNA molecule is shown to the right. List the complementary strand below.

Activity B:

DNA replication
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 eases 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.
  1. Notice that two groups of Nucleotides appear on the right. What are the three parts of a nucleotide? 
  2. 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? 
  3. 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?
Think and discuss: Why is DNA replication such an important process? 
Multiple Choice:
B         1. Which of the following strands match ATTCGG?
D         2. Which of the following could be a DNA nucleotide?
B         3. At the end of replication, how many DNA molecules are there?

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