DNA - The Star of the Show
Lesson 1 of 6
Objective: SWBAT apply their understanding of DNA's structure and function to construct an explanation of how the DNA sequences determine the type of protein that is create.
Hook - DNA Brain Dump
Students will take the opportunity to record everything they know about DNA through an activity called a Brain Dump. There is no pressure for assessment for this activity and no specific guidelines except that students need to write for at least one minute straight! Students are encouraged to incorporate all details that are associated with DNA - structure, function, genetics, previous life science courses, ect.
After two minutes, students will turn to their partner and share their three most interesting facts from their paper. Students are encouraged to record their partner's ideas to their Brain Dump list if they hear new or interesting information.
Student volunteers will be asked to share their best, most interesting fact with the class.
Brain Dumping is a strategy that encourages students to activate prior knowledge of the topic in an effort to build confidence and interest for the students either as an introduction or a closing activity for the lesson.
DNA Brain Dump - Student Work Samples - The work samples demonstrate a large range of student knowledge and understanding of the structure and function of DNA. Some students appear to have read the textbook last night, while others are still trying to catch up and learn the content.
Students will watch this one-minute video as a quick review to make sure all students have the basics of DNA structure:
Students will record the DNA Introduction Lecture Notes to solidify their understanding of how scientists analyzed laboratory data to create an accurate model of DNA's structure. The Lecture Notes go into detail regarding the structure of DNA using base pairing and hydrogen bonds.
3 Investigations That Led To Our Understanding Of DNA
- Griffith's Experiment: How do certain types of bacteria cause pneumonia?
- Significant Outcome: Genetic information could be transformed from one bacterium to another. (transformation)
- Avery's Experiment: Which molecule in the heat killed bacteria was needed for transformation?
- Significant Outcome: The nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next.
- Hershey –Chase Experiment: Which part of the virus enters the infected bacteria cell?
- Significant Outcome: The genetic information in the bacteriophage is DNA (not protein)
Conclusions About DNA From Lab Data:
The DNA molecule is a double helix. Think of it as a ladder that has been twisted into a spiral. The outside of the ladder is made up of alternating sugar and phosphate groups. The sugar is called deoxyribose. The rungs of the ladder are made up of nitrogen-containing bases. There are four different nitrogen-containing bases in DNA:adenine (A), guanine (G), cytosine (C), and thymine (T). These four bases are of two types: purines and pyrimidines. Purines are large double-ring structures. Adenine and guanine are purines. Pyrimidines are smaller single-ring structures. Cytosine and thymine are pyrimidines. Inside the DNA ladder, two bases pair up to make a "rung." One base sticks out from each sugar-phosphate chain toward the inside of the ladder. It forms a pair with a base sticking out from the opposite sugar-phosphate chain. Only three rings can fit between the two sugar-phosphate chains, so a pyrimidine (one ring) and a purine (two rings) form a pair. Because of the chemical structures of the bases, adenine always pairs with thymine, and cytosine always pairs with guanine.
DNA and Proteins
DNA is called the blueprint of life. It got this name because it contains the instructions for making every protein in your body. Why are proteins important? Because they are what you muscles and tissues are made of; they synthesize the pigments that color your skin, hair, and eyes; they digest your food; they make (and sometimes are) the hormones that regulate your growth; they defend you from infection. In short, proteins determine your body's form and carry out its functions. DNA determines what all of these proteins will be.
Teacher Preparation: Copy the Constructing a Paper Helix Handout
- With what base does adenine (A) pair?
- With what base does guanine (G) pair?
- What is the smallest unit of DNA called?
- What is the shape of the DNA molecule?
- Which bases are purines?
- Which bases are pyrimidines?
- Why must a purine pair with a pyrimidine?
- What is the name of the sugar in the DNA backbone?
- Suppose you know that the sequence of bases on one DNA strand is AGCTCAG. What is the sequence of bases on the opposite strand?
- Assume that a 100-base pair DNA double helix contains 45 cytosines. How many adenines are there?
DNA Review Questions - Student Work Samples - Most students seem to have a strong understanding of the structure of DNA, but still need to practice the function of DNA as it relates to the structure of proteins that it creates.
Close - DNA's Next Role
The class will review student responses to the DNA Modeling activity in a whole group discussion. Students will then turn to their partners and discuss if there the sequencing of base-pairs is important to the function of the cell/organism. Students will have 2-3 minutes to reference their lecture notes, textbooks, and each other's creative thinking.
Students will respond to the following prompt as a 1-2 paragraph homework assignment:
"How does the structure of the DNA model that the class assembled during today's lesson determine the structure of the proteins that will be created?
Students are encouraged to look up the concepts of transcription and translation in their textbook for inspiration. They are also reminded to use the introductory paragraph of today's activity: DNA is called the blueprint of life. It got this name because it contains the instructions for making every protein in your body. Why are proteins important? Because they are what you muscles and tissues are made of; they synthesize the pigments that color your skin, hair, and eyes; they digest your food; they make (and sometimes are) the hormones that regulate your growth; they defend you from infection. In short, proteins determine your body's form and carry out its functions. DNA determines what all of these proteins will be.