DNA - The Molecule of Life

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Objective

SWBAT to describe structure and function of DNA.

Big Idea

Students learn the structure and function of DNA.

Engage

10 minutes

To engage and assess student prior knowledge I conduct a formative assessment probe.  This probe gives me baseline data which I can use to modify my lessons objectives.

The formative assessment probe is as follows:

Four friends were talking about human DNA, genes, and chromosomes.  They each had different ideas about where these structures were found.  This is what they said.

Nancy:"I think DNA is found on genes."

Breanna:"I think chromosomes are found on genes."

Mario:"I think genes are found on DNA."

Garrett:"I think chromosomes are found on DNA."

Whom do you agree with the most?  ____________ Explain why you agree.

Teacher Note:  The best answer is Mario's "I think genes are found on DNA."  Genes are the basic structural and functional unit of heredity.  They are found on chromosomes, which are made up of DNA.  A gene is a segment of DNA that has a specific location on a chromosome.  Humans have 23 pairs of chromosomes

After the probe, I show students the following video titled DNA:  The book of you, a TED-Ed resource. This video introduces students to DNA -- specifically its function.

As students watch video, they answer the following questions:

1.  Hanson says, " There are more cells in the human body than there are:

a.  Stars in the Milky Way

b.  Apartments in Manhattan

c.  Golf ball in the PGA tour

d.  Fish in the sea

 

2.  The entire genome (or, "the book of you") is contained inside the _______ of the cell.

a. Mitochondria

b. Cell Wall

c. Nucleus

d. Lysosomes

 

3.  Explain in your own words how some cells know "how" to be muscle and some know "how" to be bone.

 

4.  Though all humans start off the same way, give a brief explanation about what make us all so different.

 

5.  How many chromosomes does the human genome contain?

a. 14

b. 23

c. 46

d. 96

 

6.  It's estimated that all the chromosomes together house about 20,000 individual instructions called...

a. genes

b. base pairs

c. chromatophores

d. lipids

Explore

30 minutes

In this section of lesson students build an edible model of DNA while learning basic DNA structure and the rules of base pairing. (Courtesy of learn.genetics.utah.edu) (SP2 - Developing and Using Models/MS-LS1-3-Develop and use a model to describe why structural changes to genes (mutations) located on chromosomes may affect proteins and may result in harmful, beneficial, or neutral effects to the structure and function of the organism/CCC - Structure and Function -Complex and microscopic structures and systems can be visualized, modeled, and used to describe how their function depends on the shapes, composition, and relationships among its parts, therefore complex natural structures/systems can be analyzed to determine how they function.)

This activity is derived from Learn Genetics, University of Utah Medical Center resources.

Prior Knowledge Needed:

DNA contains heritable instructions for building and maintaining an organism.

Key Concepts:

DNA structure, double helix, base pairing

Materials:

• DNA Edible Model (Student Handout)
• Licorice sticks (e.g., Twizzlers)– 2/student or group
• Colored marshmallows– 9 green, 9 pink, 9 yellow, and 9 orange/student or group
• Toothpicks– 12/student or group • Paperclips– 5/student or group • Masking tape– 1/several groups 

Learning Objectives:

• Students will be able to describe the structure of the DNA molecule.
• Students will be able to explain the rules of base pairing.
• Students will understand that information is stored within the DNA molecule inthe form of a sequence of chemical bases, each referred to by the first letter of its name (A, T, C and G). 


Teacher Note:  I have included DNA Edible Model (Teacher Handout) which contains further directions and possible extensions for model.

Explain

10 minutes
In this section of lesson students visit cK-12 to read DNA, the Genetic Material.  This reading reviews the following topics:
  • DNA structure
  • Chromosomes
  • Genetic Code
  • Base Pairing
Students answer the following questions as the complete reading:
  1. Describe the structure of DNA.
  2. What does a nucleotide consist of?
  3. What are the base-pairing rules?
  4. If one DNA strand reads CCGTAATGCAT, what will be the sequence of the complimentary strand?

After reading I show students the following video titled The Twisting Tale of DNA, a TED-Ed resource.  The video discusses and answers the following prompt:

What do a man, a mushroom, and an elephant have in common? A very long and simple double helix molecule makes us more similar and much more different than any other living thing. But, how does a simple molecule determine the form and function of so many different living things? 

As students watch video they answer the following questions:

 

1.  Every cell of every living thing on earth contains all the information it needs to create and duplicate and make variations of:

a.  itself

b. any other kind of cell

c.  red blood cells

d.  proteins

 

2.  DNA is made of chains of four smaller molecules called:

a.  nucleotides

b.  mitochondrial bases

c.  life blocks

d.  DNAbiers

 

3.  The four differing nucleotide parts, called bases, are made of a few:

a.  Carbon and oxygen atoms

b.  hydrogen atoms

c.  Nitrogen and phosphorus atoms

d.  All of the above

 

4.  You can think of DNA as a great library of information that exists to do one thing only.  What is that thing?

a.  Build other double helix models of information

b.  Tell the brain how to construct the body

c.  Store data about what worked and what didn't 

d.  Direct the building of different protein molecules

Elaborate

5 minutes

In this section students elaborate on what they have learned in previous lesson activities by visiting Molecules of Inheritance courtesy of Learn.Genetics.

In this site student are able to learn more in depth about the topics below.

WHAT IS DNA?

Get to know DNA, the molecule that holds the universal code of life.

BUILD A DNA MOLECULE

Find out how the DNA code letters A, C, G, and T make a DNA molecule by building one yourself.

WHAT IS A GENE?

Take a look at genes, the instructions for building a body.

THINGS YOU MAY NOT KNOW ABOUT DNA

Put an end to these common misconceptions about DNA and Heredity

Directions:

Students complete this activity as a jigsaw activity.  Since my students work in collaborative groups of four, I assign each person one of the above topics. Each student is required to take notes on their topic and report to their group at the end of class.  Students use Jigsaw Graphic Organizer to complete activity.  Students use graphic organizer to take write down important ideas and to write a concise summary of topic.  In addition graphic organizer allows students to take notes on other students topics.

Evaluate

5 minutes

In this section of lesson students complete an Exit Slip.

The exit slip assesses students understanding of DNA structure, base pairing rules, and the relationship between DNA's structure and ability to be the building block of life.

Students are able to use their notes to complete exit slip, specifically students should use their model they crated to answer the questions specifically regarding DNA structure.  In terms of how DNA allows it be the secret code of life this question is to assess students entry level of understanding how its predictable structure allows it to be replicated.  This will be studied further when students learn about transcription and translation.