National Institutes of Health U.S. Department of Health and Human Services
DNA from the Beginning Study Guide
This lesson is based on an award-winning Web site - DNA from the Beginning [dnaftb.org] - an animated primer on the basics of DNA, genes and heredity. The Web site is organized around key concepts. The lesson that follows concentrates on high school level activities located under the Molecules of Genetics [dnaftb.org] section of the Web site.
The science behind each concept is explained on the site using animations, an image gallery, video interviews, problems, biographies and links. In addition to the Molecules of Genetics covered in this lesson, the Web site includes two other sections of possible interest for further study: Classical Genetics (basics) and Genetic Organization and Control (advanced level).
This study guide will be used to familiarize students with the Molecules of Genetics section of the DNA from the Beginning [www.dnaftb.org] Web site.
Middle school-High school
Two class periods
By the end of this lesson, students will be able to:
Give examples of one scientific discovery building on another.
Summarize the sequence of discoveries that led to our current understanding of DNA.
Start the lesson by giving out the list of numbered questions (#15-28) provided below. The numbering of the questions corresponds to the numbering of the corresponding concept headings presented on DNA from the Beginning [www.dnaftb.org]. The corresponding concept headings with additional information are located on the Web site under the section entitled Molecules of Genetics [www.dnaftb.org]. Students may click on the Molecules of Genetics button on the Web site home page to reach the corresponding concept headings (#15-28 are listed down the right side of the Web page) that they may click on to get the information they need to answer the questions posed in this lesson. After answering each question, students may click on the PROBLEM button located at the bottom of each concept page and use their problem-solving skills further.
Molecules of Genetics Questions
#15. DNA and proteins are key molecules of the cell nucleus.
Why did most scientists think that proteins were the most likely candidates to transfer hereditary information from one generation to another?
In the PROBLEM section: How did you calculate that in a tetranucleotide block in which the order is random and each nucleotide is used only once, there could be 24 different combinations?
#16. One gene makes one protein
What did Archibald Garrod propose as the cause for the phenotype of the disease of dark urine?
How did George Beadle and Edward Tatum prove what Garrod proposed?
What concept was developed from the work with bread mold of Beadle and Tatum?
From the PROBLEM section: How can you decide that the order of the synthesis pathway is MutC, MutA, MutE?
#17. A gene is made of DNA.
How did Oswald Avery show that the transforming principal was DNA?
Why did Avery identify a gene as the genetic molecule that transfers hereditary information and not a protein?
From the PROBLEM section: Why does adding DNA from the R strain not transform the R to S?
#18. Bacteria and viruses have DNA too.
What evidence indicated that bacteria had genes?
How did Alfred Hershey's experiments with viruses support Avery's earlier experiments with bacteria?
From the PROBLEM section: When the F factor is integrated into the bacterial chromosome, can it still act as a donor in a conjugation cross?
#19. The DNA molecule is shaped like a twisted ladder.
What type of technology helped to show that DNA was shaped like a twisted ladder?
What part of the molecule forms the rungs of the ladder?
What part of the molecule forms the sides of the ladder?
From the PROBLEM section: How can you illustrate the structure of DNA as a right-handed double helix?
#20. A half DNA ladder is a template for copying the whole.
How did the discovery of the enzyme DNA polymerase play in the understanding for the process of DNA replication?
What is the difference between the conserved strand of DNA and the complementary strand?
From the PROBLEM section: Meselson and Stahl showed that DNA replication is semi-conservative. What would the contents of tubes 1-4 look like to illustrate this finding?
#21. RNA is an intermediary between DNA and protein.
What is the "Central Dogma?"
What is the difference between transcription and translation of the DNA message?
From the PROBLEM section: How would you describe two types of genetic mutations? How do the mutations change the protein product?
#22. DNA words are three letters long.
How does a three-letter code make it possible to make 64 different combinations?
Why was it believed that it was necessary to have a three-letter code?
What is a codon?
From the PROBLEM section: Why can there be more then one possible mRNA sequence for a peptide sequence?
#23. A gene is a discrete sequence of DNA nucleotides.
How would you define a gene?
What is DNA sequencing?
From the PROBLEM section: How do you read an autoradiogram of a gene sequencing gel?
#24. The RNA message is sometimes edited.
What happens to mRNA when there is no binding region of DNA to match?
What is the difference between an intron and exon?
From the PROBLEM section: What causes a doublet to form in a gel sequence?
From the PROBLEM section: How can you detect the exon regions on an electron micrograph of a DNA/RNA hybrid?
#25. Some viruses store genetic information in RNA.
How does a retrovirus carry out the process of infection?
What type of enzyme is necessary for reverse transcription to take place?
From the PROBLEM section: How can a viral vector be a useful tool in research?
#26. RNA was the first genetic molecule.
Why does RNA play so many roles in the flow of genetic information?
Why bother storing genetic information in DNA, if RNA alone could do the job?
From the PROBLEM section: How was it proved that base pairing was important for a self-splicing reaction in RNA?
#27. Mutations are changes in genetic information.
What types of DNA mutations can occur?
What are the possible results of DNA mutations?
From the PROBLEM section: Why is the number of mutations proportional to the length of time that two groups have been separated?
#28. Some types of mutations are automatically repaired.
What might be the central role of DNA repair enzymes?
What are the positive results of DNA mutations?
From the PROBLEM section: Why do you think UV light inhibits DNA replication?
Review the homework assignments by discussing the answers to the questions. You can have the students discuss the problem-solving activities and how they were able to work through them. Group discussion of the meta-cognition may help students think through other problems in a similar manner.
To extend this lesson, click on the BIO button and LINKS button located at the bottom of the Molecules of Genetics [www.dnaftb.org] under the answers to the specific questions (#15-28).