Teacher

The national standards that will be addressed in this lesson include the understanding of the structure and function of DNA, the amino acids involved in DNA formation, and how the chemical and structural properties of DNA explain how the genetic information is coded. This lesson will also address science as inquiry standard by as they combine previous knowledge with the current exploration to use scientific reasoning and critical thinking to develop their understanding of science.

The DESE frameworks that will be addressed in this lesson are those that describe that DNA contains the hereditary information (the information that makes each of us unique) and ultimately encodes for the information for all cell function.

This lesson will introduce DNA, genes, chromosomes, the chemicals that make up DNA, etc. After the basic information, students will do an experiment comparing exploration activity one of strawberry DNA extraction with Exploration Activity Two (application) DNA extraction from cheek cells. Knowing that DNA can be separated will give them a base of understanding for future lessons in biology, evolution, biotechnology, and health technology, and Forensic Science.

While working in groups, the students will conclude the exploration by completing the following assignment:

Match the procedure with what it is doing to help isolate the DNA from the other materials in the cell:

______Dissolve cell membranes ______Dissolve cell membranes B. Filter your strawberry extract through cheesecloth

______Precipitate the DNA ______Precipitate the DNA C. Mix in a detergent solution

______Separate organelles, broken cell D. Layer cold ethanol over filtered extract

Applying your previous knowledge regarding cells, DNA is soluble in water, but not in ethanol. What does this fact have to do with our method of extraction? Explain what happened when the ethanol came in contact with the strawberry extract.

Through the use of Tour of the Basics website, the students will draw together the basic introduction to DNA. They will take notes covering: DNA, Chromosomes, genes, amino acids, and the role proteins play. Teacher will introduce the website: Tour of the Basics. We will go through this website as a class and the students will takes notes on the following topics as we proceed.

What is DNA? Deoxyribonucleic acid – nucleic acid that stores and transmits genetic information from one generation of an organism to the next by coding for the production of a cell’s proteins. (The instructions that provide all of the information necessary for a living organism to grow and live, these instructions tell the cell what role it will play in your body)

What are genes? instruction manuals for our bodies. They are the directions, the “blueprint”, for building all the proteins that make our bodies function. Each gene in the DNA encodes information about how to make an individual protein.

Students will apply newly acquired knowledge regarding DNA while analyzing their own check cells.

Students collect cheek cells by rinsing their mouths with a saline solution. The saline solution keeps the cells from lysing, or splitting open, too soon. The cheek cells are separated from the mouthwash by centrifugation. (spinning them in a centrifuge). The cells are heavier than the saline solution so they sink to the bottom and form a clump or pellet . The cell pellet remains stuck to the bottom of the tube and the saline solution can be poured off. Lysis buffer is added to the cell pellet in order to split the cells open (the DNA must be released from inside the nucleus). Lysis buffer contains soap (to break apart the fatty membranes), salts and ions (to increase the osmotic pressure outside the cell and help break apart the membranes) and buffers (to maintain the pH of the solution). The cells are incubated in a hot water bath in order to denature the cytoplasmic enzymes which break apart DNA. Students add a concentrated salt solution which changes the polarity of the solution; DNA dissolves in ionic solutions while fats, carbohydrates and many proteins will not. Centrifugation separates the DNA from the "junk" (proteins, carbohydrates and fats). The DNA is precipitated from the ionic solution by the addition of cold ethanol.

Students will answer questions included with the lab procedure as well as to compare and contrast the two lab activities used in this first lesson.

Questions	Strawberry	Cheek Cells
What are the cell characteristics?
What lyses the cell and nucleus?
What protects the DNA?
What precipitates the DNA?
Amount of DNA
Description of DNA
Changes in protocol

For students to get an understanding of the history of this scientific concept, they will review the timeline from pre-1920’s found at www.dnai.org and focus on the following scientists:

Gregor Mendel (1822-1884), Father of Genetics - Gregor Mendel, through his work on pea plants, discovered the fundamental laws of inheritance. He deduced that genes come in pairs and are inherited as distinct units, one from each parent. Mendel tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits. He recognized the mathematical patterns of inheritance from one generation to the next. Mendel's Laws of Heredity are usually stated as:

1) The Law of Segregation: a gene pair defines each inherited trait. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair. Offspring therefore inherit one genetic allele from each parent when sex cells unite in fertilization.

2) The Law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another.

3) The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant.

The genetic experiments Mendel did with pea plants took him eight years (1856-1863) and he published his results in 1865. During this time, Mendel grew over 10,000 pea plants, keeping track of progeny number and type. Mendel's work and his Laws of Inheritance were not appreciated in his time. It wasn't until 1900, after the rediscovery of his Laws, that his experimental results were understood.

Friedrich Miescher (1844-1895) - isolated the first crude preparation of DNA, he just didn’t know it. He named it nuclein.

Carl Erich Correns (1864-1933) - Correns (with credit to de Vries) restated Mendel's results, giving us Mendel's law of segregation and Mendel's law of independent assortment.

Hugo de Vries (1848-1935) - He completed most of his hybridization experiments without knowing about Mendel's work. Based on his own results, de Vries drew the same conclusions as Mendel.

Erich von Tschermak-Seysenegg (1871-1962) - Tschermak, like de Vries and Correns, independently derived "Mendelian" laws of inheritance from his plant experiments. Tschermak was a plant breeder, and his hybridization experiments were done with the idea of improving crops using the laws of heredity. He did most of the work himself, and produced high-yielding food crops such as wheat, barley, and oats.

Thomas Hunt Morgan (1866-1945) - established the chromosomal theory of inheritance. Morgan and his students did ground-breaking genetic research using Drosophila melanogaster, fruit flies. Though initially against the idea that the behavior of chromosomes can explain inheritance, Morgan became the leading supporter of the idea. Morgan and his students (Alfred Sturtevant, Calvin Bridges, Hermann Muller and others), developed the ideas, and provided the proof for the chromosomal theory of heredity, genetic linkage, chromosomal crossing over and non-disjunction.