1. Modeling DNA Structure
Activity 10
Modeling DNA Structure

2. Read the introduction on p.328
Look at the diagram on the introduction page.
What is the relationship between DNA…
genes…chromosomes?

3. What is the relationship between…
Get Started
What is the relationship between…
The cell
Nucleus
chromosomes
DNA
genes

4. What are the subunits of DNA? What are the parts of these subunits?
DNA Structure
What is DNA?
What are the subunits of DNA?
What are the parts of these subunits?
Why is DNA important to living things?
What is it’s shape?
Explain that DNA has the shape of a double helix, and that despite its size, it is relatively simple in structure. Do not explain or reference nucleotide pairing at this point. For more information on having this class discussion see the Teacher’s Edition for this activity.
These images are from Transparency 10.1, “DNA Structure.”

5. What is the molecular structure of DNA?
Challenge
What is the molecular structure of DNA?
Read about the discovery of the DNA structure on p. 330

6. Show students the deoxyribose sugar, the phosphate group, and the nitrogenous-base pieces from the DNA model kit. For more information see the Teacher’s Edition for this activity.

7. DNA Nucleotides
Show the class the four nucleotides and their corresponding kit pieces. Point out that each nucleotide has the same deoxyribose sugar and phosphate group, but the nitrogenous (nitrogen-containing) base attached to the sugar-phosphate backbone can vary.
These images are from Transparency 10.2, “ DNA Nucleotides.”

8. DNA Nucleotides
Depending on your instructional goals, you may wish to explain that each of the four nitrogenous bases has its own molecular structure, but all are based on cyclic molecules made of carbon and nitrogen rings.
These images are from Transparency 10.2, “ DNA Nucleotides.”

9. Hydrogen Bonds
The sides of DNA are made of alternating phosphate & sugar groups
The “rungs” of DNA are made of complementary base pairs
The bases can only bond a certain way
Look at table on p. 331 to see if you can determine the base pairing pattern
Discuss the role of hydrogen bonds in DNA. See the Teacher’s Edition for this activity for more information.
This image is from Transparency 10.1, “DNA Structure.”
The Teacher’s Edition for this activity contains more information on having a class discussion on the historical discovery of the structure of DNA, and on assisting students in drawing the correct conclusions about nucleotide pairing in DNA. Be sure students have figured out the proper rules of nucleotide pairing before continuing to the next slide.

10. Antiparallel DNA
Develop the concept of antiparallel strands of DNA. For more information see the Teacher’s Edition for this activity.
This image is from Transparency 10.3, “Antiparallel DNA.”

11. Double-helix Structure
Look at the images of DNA on p. 332 in your text
Note similarities & differences between the images
SIMILARITIES: double helix structure; S-P backbone; base pair “rungs’
DIFFERENCES: <TOP> shows base pairs in center; drawn diagrams….<BOTTOM> computer generated images…<TOP LEFT> shows Hydrogen bonds
Connect three or four of the students’ completed DNA models end-to-end. Twist this longer model to demonstrate the double-helix structure of DNA. See the Teacher’s Edition for more information about having this class discussion.

12. DNA Images
Procedure Step 11 serves as a Quick Check to assess students’ grasp of the structure of DNA and to make sure they can describe the shape and key structural components of DNA.
These images are from Transparency 10.4, “DNA Images.”

13. ANALYSIS 2
What nucleotide sequence would bond with the following strand: 5’ ATCGCC 3’?
3’ TAGCGG 5’

14. ANALYSIS 3
Arrange the following cell structures form the smallest to the largest:
Cell…DNA…Chromosomes…Gene…
Nucleus
Gene…DNA…chromosome…nucleus…cell

15. Analysis 4
The table below shows the number of base pairs in the DNA of selected organisms. From the data in the table, what can you say about the amount of DNA contained in the cells of these three organisms?
Amount of DNA in an Average Cell of Selected Organisms
Organism
Number of Base Pairs
E. Coli
4.7 million
Corn (Zea mays)
2.5 billion
Human (Homo sapiens)
3.3 billion
To provide students with a sense of the amount of DNA contained in the average human cell, explain that the model they built was eight base pairs (bp) in length. The combined length of all of the DNA in the 23 human chromosome pairs (46 chromosomes) is approximately 3 billion base pairs.

16. deoxyribonucleic acid (DNA) hydrogen bond nucleotide
Key Vocabulary
base pair
double helix
deoxyribonucleic acid (DNA)
hydrogen bond
nucleotide
sugar-phosphate backbone
See Teacher Resources III: Literacy for more information on key vocabulary and the most effective strategies to enhance student vocabulary learning.
Note that bold words are formally defined in this activity. Words in regular font are used in the activity, but not formally defined. The definition of a key vocabulary word should not be discussed as a class prior to the formal definition being introduced.