A pre-assessment will be given to the students before the unit is delivered. The teacher will set the stage with a series of questions for students to think about: What is it that tells our cells to produce saliva? What directs a tiny embryo to develop into a baby? What tells skin cells to grow after cutting your hand? The teacher will present a series of historical experiments and the resulting data. Students will be asked to think critically and use the data to make inferences as to what the hereditary material is and its structure. The teacher will represent DNA replication and protein synthesis using a constructed model. In groups, students will analyze original and mutated DNA segments to discover the importance and effects of mutations on protein synthesis. As a class, the causes and effects of genetic disorders will be discussed. Students will also extract DNA from an onion, cut it with restriction enzymes, and analyze it using gel electrophoresis. They will also use their understanding of restriction enzymes and gel electrophoresis to analyze real world problems, such as paternity and crime scene investigations.
Knowledge: Big Ideas
Past experiments and observations have led to the development of many modern scientific theories and a large scientific knowledge base. Previous work done by Griffith, Avery, Hershey, Chase, Chargaff, Franklin, Watson, and Crick has contributed to the understanding of the hereditary material, DNA.
DNA allows heritable traits to be passed from parent to offspring in sexual or asexual reproduction. The parent DNA must first be replicated to create an identical copy of itself, which can then be passed on to an offspring. DNA, being made of two complementary strands, uses each strand to serve as a template for a new complementary strand. Thus, every time DNA replicates, each product contains one old strand of DNA and one new strand of DNA.
DNA resides in the nucleus of every cell and is the hereditary material that dictates all cellular activity. In order to fit inside of the nucleus, the DNA is highly compressed. It contains the instructions for assembling proteins. Many proteins are enzymes, which catalyze and regulate chemical reactions within organisms. A gene contains DNA that controls a particular trait, such as blood type or eye color. Therefore, the DNA of a particular gene codes for a specific protein that performs a certain function.
DNA undergoes a series of steps in order to be coded into a specific protein. This is known as the central dogma, which says that DNA codes for the production of mRNA, which is processed before leaving the nucleus to be translated into a specific protein by a ribosome. Any alteration in the DNA sequence may lead to an alteration in the amino acid sequence and possibly change the protein that is produced. Since different proteins perform different functions, the trait expressed by an individual will be different.
Knowledge: Experiences, Patterns, and Explanations
Observations or experiences (examples, phenomena, data)
1. Describe how genetic material is passed from parent to young during sexual and asexual reproduction.
Specific Topic Objectives
1. Explain how DNA replicates.
Telling the story
2. Explain how specific proteins are constructed from DNA.
3. Explain how a mutation in a nucleotide sequence may show up as a change in the trait of an individual (U, III. 3. H. 3: Explain how new traits may be established in individuals/populations through changes in genetic material (DNA)).
4. Describe the historical discoveries and experimental data about DNA that led to the discoveries of its role and structure (R, II.1. H. 7: Describe the historical, political, and social factors affecting developments in science).