The Arizona STEM Acceleration Project
Building DNA Model
Building DNA Model
An 8th grade STEM lesson
Manal Kareem
June 2023
Notes for teachers
List of Materials
Arizona Science Standards
8.L3U1.9 Construct an explanation of how genetic variations occur in offspring through the inheritance of traits or through mutations.
Science and Engineering Practices
● develop and use models
● plan and carry out investigations
● construct explanations and design solutions
● engage in argument from evidence
● obtain, evaluate, and communicate information
Mathematical Practices
5. Use appropriate tools strategically.
Objective(s):
Today we will learn about the nitrogenous bases. Students should become familiar with the four nitrogenous bases- Adenine (A), Thymine (T), Cytosine ©, and Guanine( G)- and understand how they pair up in DNA.
Today we will learn and comprehend base pairing rules: Students should grasp the concept of complementary base pairing, where adenine always pair with thymine and cytosine pair with guanine.
Today we will foster teamwork and collaboration by work in pairs or small group to build the DNA model fostering collaboration ,communication, and teamwork skills.
Agenda (lesson time)
Review what is DNA? ( 5 minutes)
What is the function of DNA in the cell? ( 5 minutes)
DNA structure ( 5 minutes)
Engineering DNA (25 minutes)
Share and present (10 minutes)
What is the DNA?
DNA is a long molecule that contains each person’s unique genetic code. It holds the instructions for building the proteins essential for the body’s function.
DNA instructions pass from parent to child, with roughly half of a child’s DNA originating from the father and half from the mother.
In human cells, most DNA is found in a compartment within the cell called a nucleus. It is known as nuclear DNA.
What is the function of DNA in the cell?
The key function of DNA in a cell is to store the genetic information that allows an organism to develop, function, and reproduce. The information encoded in DNA can be passed on from one generation to the next and acts as a biological instruction manual that makes each organism unique.
To follow the instructions in DNA, a cell must first copy a gene into a form of RNA called messenger RNA (mRNA). This process is known as transcription. In many cases the information contained within DNA needs to be translated into a protein in order for the instructions to be carried out, as proteins take care of most of the work in cells, performing a wide variety of critical functions.
How is DNA Structured?
DNA consists of two strand, each of the two strands is a long sequence of nucleotides. These are the individual units of DNA and they are made of:
There are four types of nitrogen-containing regions called bases, Including:
How is DNA Structured?
The order of these four bases forms the genetic code, which is the instructions for life.
The bases of the two strands of DNA are stuck together to create a ladder-like shape. Within the ladder, A sticks to T, and G sticks to C to create the “rungs.” The length of the ladder forms through the sugar and phosphate groups.
Design the DNA Model
Hands-on Activity Instructions
Step 1: Preparing the materials , cut 2 pipe cleaners into equal lengths (around 12 inches or 30 centimeters) to represent the DNA backbone ( sugar), and cut 2 straws into small pieces of 2 inches to represent the -phosphate on the backbone
Step 2: Creating the DNA backbone, take two different-colored pipe cleaners and insert the small pieces of straws into the 2 pipes cleaners. This represents the sugar-phosphate backbone of DNA.
Step 3: Adding the nitrogenous bases using the colored small pieces of pipe cleaners. Students must assign each color to represent one of the four nitrogenous bases—adenine (A), thymine (T), cytosine (C), and guanine (G). Make sure to use complementary base pairing: A pairs with T, and C pairs with G.
Hands on Activity Instruction
Step 4: Securing the model (optional) If desired, tape or glue the ends of the pipe cleaners .
Step 5: Exploring the model Once the DNA model is complete, students can examine the structure, observe the double helix shape, and explore how the nitrogenous bases pair up. They can also discuss the significance of base pairing and how it relates to DNA replication and protein synthesis
When done, students must practice the DNA replication process by unwind the DNA molecule, and each strand serve as a template for the synthesis of a new complementary strand, resulting in two identical DNA molecule. Both DNA molecules must be identical.
Assessment
Analysis & Discussion
Students will discuss the following questions in groups and then write each question with individual answers in the Lab Notebook.
1. What does DNA looks like?
2. Explain the importance of the nitrogenous bases in DNA.
3. If a scientist needs to remove (extract) DNA from the cell, what parts of the cell would be destroyed?
Differentiation
Write on the board that Adenine is most connected with Thymine and Guanine with Cytosine.
Start your own model of DNA to show to students as needed.
Students were free to pick what colors they should refer to the nitrogenous bases.
Remediation
Extension/Enrichment
Use the model to explain the process of DNA replication and transcription.
Discuss the role of DNA in heredity and how variations in DNA sequences can lead to genetic diversity.
Explore the structure and function of DNA in different organisms.