DNA Structure B1YvM
DNA Structure & ReplicationHow is the genetic information stored and copied?Why?DNA is the molecule of heredity. It contains the genetic blueprint for life. For organisms to grow andrepair damaged cells, each cell must be capable of accurately copying itself. So how does the structure ofDNA allow it to copy itself so accurately that cells can then replicate during cell division?Model 1: The Structure of DNALadder model of DNAHelix model of DNAAdenineThymineGuanineCytosine1. What are the 3 parts of a nucleotide?2. What kind of sugar is found in a nucleotide?3. Which nucleotide component contains nitrogen? HSPI – The POGIL Project Limited Use by Permission Only – Not for DistributionDNA Structure B1YvM1
4. How many different nitrogen bases are there? Name them.5. Circle a single nucleotide on each side of the ladder model of DNA.6. In the ladder model of DNA, how are the nucleotides arranged?7. Which components of the nucleotides pair together to form the “rungs” of the ladder?8. On the ladder model of DNA label each of the bases with the letter A, T, C or G.9. Which components of the nucleotides form the sides (backbone) of the ladder?10. When one nucleotide contains adenine, to what type of base will the adenine attach on theopposite nucleotide strand?11. How many hydrogen bonds (lines) connect these two bases?12. When one nucleotide contains cytosine, to what type of base will the cytosine attach on theopposite nucleotide strand?13. How many hydrogen bonds connect these two bases?14. Using complete sentences, with your group write a rule for how the bases are arranged in theladder model of DNA.Read This!Erwin Chargaff investigated the ratio of nucleotide bases found in the DNA from avariety of organisms. From his research, as well as research by Rosalind Franklinand Maurice Wilkins, Watson and Crick developed the base-pair rule during their HSPI – The POGIL Project Limited Use by Permission Only – Not for Distributionrace to discover the structure of DNADNA Structure B1YvM2
15. The ladder model of DNA is a simplified representation of the actual structure and shape of aDNA molecule. According to the final diagram in Model 1, what is the actual shape of the DNAmolecule?16. The DNA molecule is usually referred to as a double helix. Explain why.Model 2: DNA Replication17. What molecule is attached to the left-hand portion of the DNA molecule?18. What type of biological molecule is this?19. Looking at the diagram, what do you think is the function of this molecule?20. What will need to be broken in order to separate the strands of DNA? HSPI – The POGIL Project Limited Use by Permission Only – Not for DistributionDNA Structure B1YvM3
21. What rule is used to join the free nucleotides to the exposed bases of the DNA?22. This type of replication is called semi-conservative replication. Considering the meaning of thesewords (semi – half; conserve – to keep), explain why DNA replication is called semi conservative.23. DNA molecules can be tens of thousands of base pairs in length. Mistakes in DNA replicationlead to mutations, which may or may not be harmful to an organism. How does semi-conservativereplication help prevent mutations during DNA replication?24. The proportions of the bases are consistent within a species; however they do vary betweenspecies. Using the base pair rules complete the following table to show the percentage of each typeof base in the five different 1282731Percentage of each type of baseGuanineCytosine192221Thymine2919 HSPI – The POGIL Project Limited Use by Permission Only – Not for DistributionDNA Structure B1YvM4
Extension QuestionsModel 3 - The Meselson & Stahl Experiment25. In the Meselson & Stahl experiment, how is the DNA in the first test tube described?26. What is the atomic mass of the N in this DNA?27. During the first replication, what is the atomic mass of the N in the bases that are added?28. How is the DNA in the second test tube (after replication) described? Discuss with your groupwhat this term means and why it is used to describe the DNA.29. The lines in the test tubes represent the DNA after it has been centrifuged (spun at high speeds toseparate molecules by weight). What is different about the position of the DNA band in the firsttest tube compared to the band in the second test tube? HSPI – The POGIL Project Limited Use by Permission Only – Not for DistributionDNA Structure B1YvM5
30. In the third test tube the DNA has been allowed to replicate again, using 14N free nucleotides.Using all the diagrams in the model, explain why there are now two bands showing in the thirdtest tube and explain why they are positioned the way they are.31. With your group draw what you would expect to see if the DNA in the third test tube were toreplicate again, using 14N free nucleotides. Draw the DNA bands in the test tube as well as theDNA molecules. Use solid lines to represent the 15N DNA and dashed lines to represent the 14NDNA. HSPI – The POGIL Project Limited Use by Permission Only – Not for DistributionDNA Structure B1YvM6
Teacher’s Guide & Answer KeyLearning Objectives:After completing the activity the students should be able to:1. Draw a simple representation of a nucleotide and name each of the three components.2. Apply the base pair rule to show how the two strands of a DNA molecule are joined and how aDNA model replicates.3. [With the Extension Questions] Explain how the Meselson and Stahl experiment supports thesemi-conservative model of DNA replication.Prerequisites:Students should have a basic knowledge of atomic mass, bonding, and biological molecules, including thefact that most enzymes end in –ase.Assessment Questions:1. In a DNA molecule, a sugar, phosphate and nitrogenous base are collectively referred to as:a. DNAb. RNAc. Nucleotided. Codon2. Explain what is meant by semi-conservative replication and why it helps ensure faithful replicationof the DNA molecule.It is called semi-conservative replication because half of the original molecule is kept and theother half is synthesized from free nucleotides. Because new nucleotides are brought inaccording to the base pair rule, it lessens the likelihood that the wrong nucleotide sequenceis created during replication.3. Use the base-pair rule to show the corresponding nucleotide sequence that would create a DNAmolecule:A T T C G C T T A A G G C C G TT A A G C G A A T T C C G G C ATeacher Tips:Question 6 can be used to introduce the concept of antiparallel strands where appropriate. Additionalenzymes involved in replication such as RNA primase and DNA polymerase are not shown, in order tokeep the model simplified. These can be introduced later of through animations such ashttp://www.johnkyrk.com/DNAreplication.html HSPI – The POGIL Project Limited Use by Permission Only – Not for DistributionDNA Structure B1YvM7
Target Responses:1. What are the 3 parts of a nucleotide? Deoxyribose sugar; phosphate; N-containing base2. What kind of sugar is found in a nucleotide? deoxyribose3. Which nucleotide component contains nitrogen? Base4. How many different nitrogen bases are there? Name them. FOUR (adenine, thymine, cytosine& guanine)5. Circle a single nucleotide on each side of the ladder model of DNA. Two complete nucleotidesshould be circled (each containing the base, and sugar and phosphate groups)6. In the ladder model of DNA, how are the nucleotides arranged? In two [anti-parallel] strands.7. Which components of the nucleotides pair together to form the “rungs” of the ladder?Nitrogenous bases8. On the ladder model of DNA label each of the bases with the letter A, T, C or G. All basesshould be labeled appropriately.9. Which components of the nucleotides form the sides (backbone) of the ladder? Sugars &phosphates10. When one nucleotide contains adenine, to what type of base will the adenine attach on theopposite nucleotide strand? Thymine11. How many hydrogen bonds (lines) connect these two bases? 212. When one nucleotide contains cytosine, to what type of base will the cytosine attach on theopposite nucleotide strand? Guanine13. How many hydrogen bonds connect these two bases? 314. Using complete sentences, with your group write a rule for how the bases are arranged in theladder model of DNA. A pairs with T and C pairs with G15. The ladder model of DNA is a simplified representation of the actual structure and shape of aDNA molecule. According to the final diagram in Model 1, what is the actual shape of the DNAmolecule? Helix16. The DNA molecule is usually referred to as a double helix. Explain why. The helix refers to thecoiled shape, but as there are two strands coiled around each other, it is a double helix. HSPI – The POGIL Project Limited Use by Permission Only – Not for DistributionDNA Structure B1YvM8
17. What molecule is attached to the unbroken portion of the DNA molecule? DNA helicase18. What type of biological molecule is this? An enzyme19. Looking at the diagram, what do you think is the function of this molecule? To [unwind and]separate the DNA strands.20. What will need to be broken in order to separate the strands of DNA? The hydrogen bondsholding the base pairs together.21. What rule is used to join the free nucleotides to the exposed bases of the DNA? The base-pairrule: A-T & C-G22. This type of replication is called semi-conservative replication. Considering the meaning of thesewords (semi – half; conserve – to keep), explain why DNA replication is called semi conservative.Because during replication, half of the original molecule is kept and the other half issynthesized from free nucleotides.23. DNA molecules can be tens of thousands of base pairs in length. Mistakes in DNA replicationlead to mutations, which may or may not be harmful to an organism. How does semi-conservativereplication help prevent mutations during DNA replication? One half of the original molecule iskept and the new strand is made from free nucleotides, which can only join according to thebase pair rule, so it lessens the likelihood that the wrong nucleotide sequence is created.24. The proportions of the bases are consistent within a species; however they do vary betweenspecies. Using the base pair rules complete the following table to show the percentage of each typeof base in the five different 128292731Percentage of each type of 29273125. In the Meselson & Stahl experiment, how is the DNA in the first test tube described? Heavy26. What is the atomic mass of the N in this DNA? 1527. During the first replication, what is the atomic mass of the N in the bases that are added? 14 Nbases are added.28. How is the DNA in the second test tube (after replication) described? Discuss with your groupwhat this term means and why it is used to describe the DNA. Hybrid DNA ( 15 N/ 14 N). Itmeans a mix or combination of two things and the DNA is now a combination of 14 N and15N nucleotides. HSPI – The POGIL Project Limited Use by Permission Only – Not for DistributionDNA Structure B1YvM9
29. The lines in the test tubes represent the DNA after it has been centrifuged (spun at high speeds toseparate molecules by weight). What is different about the position of the DNA band in the firsttest tube compared to the band in the second test tube? In the first tube the band is lowerdown, closer to the bottom of the tube, compared to the band in the second test tube.30. In the third test tube the DNA has been allowed to replicate again, using 14N free nucleotides.Using all the diagrams in the model, explain why there are now two bands showing in the thirdtest tube and explain why they are positioned the way they are. Each hybrid DNA separatedand using the free 14 N nucleotides four molecules of DNA were made. Two contain only 14 Nnucleotides, so they are light, and the other two still contain a mix of 14 N and 15 N so theyare hybrid. This creates two bands as shown in the diagram.31. With your group draw what you would expect to see if the DNA in the third test tube were toreplicate again, using 14N free nucleotides. Draw the DNA bands in the test tube as well as theDNA molecules. Use solid lines to represent the 15N DNA and dashed lines to represent the 14NDNA.Should have two hybrid strands and six light strands. The light band in the test tube shouldnow be drawn thicker to represent the fact that there is substantially more light DNAcompared to hybrid DNA. HSPI – The POGIL Project Limited Use by Permission Only – Not for DistributionDNA Structure B1YvM10
DNA molecule. According to the final diagram in Model 1, what is the actual shape of the DNA molecule? Helix 16. The DNA molecule is usually referred to as a double helix. . half; conserve – to keep), explain why DNA replication is called semi conservative. Because during replication, half of the original molecule is kept and the other half .
Genetic transformation and DNA DNA is the genetic material in bacterial viruses (phage) The base-pairing rule DNA structure. 2. Basis for polarity of SS DNA and anti-parallel complementary strands of DNA 3. DNA replication models 4. Mechanism of DNA replication: steps and molecular machinery
DNA Structure and Replication 3 Model 2 - DNA Replication Direction of DNA helicase DNA helicase Free Nucleotides 11. Examine Model 2. Number the steps below in order to describe the replication of DNA in a cell. _ Hydrogen bonds between nucleotides form. _ Hydrogen bonds between nucleotides break. _ Strands of DNA separate.
Recombinant DNA Technology 3. Recombinant DNA Technology 600 DNA ISOLATION AND PURIFICATION Basic to all biotechnology research is the ability to manipulate DNA. First and foremost for recombinant DNA work, researchers need a method to isolate DNA from different organisms. Isolating DNA from bacteria is the easiest procedure because bacterial cells
1 DNA Structure & Replication (Outline) Historical perspective (DNA as the genetic material): Genetic transformation DNA as the transforming agent DNA is the genetic material in bacterial viruses (phage) Historical perspective (Structure of DNA): Identifying ribose and deoxy ribose
2. At the end of DNA replication, (four/two) new strands of DNA have been produced, giving a total of (four/six) strands of DNA. 3. New DNA is replicated in strands complementary to old DNA because production of new DNA follows the rules of (base pairing/the double helix). Identifying Structures On the lines corresponding to the numbers on the .
The Insider’s Guide to DNA 1 Family history is in our DNA We all have DNA. It’s the genetic code that tells your body how to build you. You inherit half of your DNA from each parent: 50% from Mom and 50% from Dad, though exactly which DNA gets passed down is random. Because they inherited their DNA in the same way from their parents, your .
DNA cytosine methylation is a major epigenetic mark in eukaryotes. In plants, the DNA methyla-tion level in the genome is controlled by de novo DNA methylation, maintenance DNA methylation and DNA demethylation. De novo methylation is mediated by RNA-directed DNA methylation (RdDM), which can occur at all cytosine contexts,
The American Revolution, 1763-1783 By Pauline Maier This essay excerpt is provided courtesy of the Gilder Lehrman Institute of American History. INDEPENDENCE The Seven Years’ War had left Great Britain with a huge debt by the standards of the day. Moreover, thanks in part to Pontiac’s Rebellion, a massive American Indian uprising in the territories won from France, the British decided to .
