Lesson Overview. The Structure of DNA

Transcription

1 Lesson Overview The Structure of DNA

2 Related Videos Stated Clearly: Bozeman Nucleic acids: Bozeman People who discovered DNA:

3 Objectives describe gene and chromosomal mutations explain how mutations may or may not result in a phenotypic change explain the basic processes of transcription and translation and their roles in the expression of genes explain the role of mrna, trna and rrna in transcription and translation explain how one gene codes for one protein explain how and why the genetic code is common to almost all organisms explain how similarities in the genetic codes of organisms are due to common ancestry and the process of inheritance explain that as more information is gathered through investigation, our understanding of the role of nucleic acids, genes, and proteins changes to incorporate that information recognize that in determining the structure of DNA, Watson & Crick had to use creativity, logic, and critical thinking to make sense of the multiple data sources presented evaluate examples and explain the possible impact of biotechnology summarize the methods of DNA analysis and manipulation evaluate the impact of biotechnology on society in terms of bioethics and religion recognize that not all questions can be answered through scientific investigation

4 Prefixes/Suffixes Bio life -ology the study of pheno appearing, seeming trans across, through, beyond

5 Key Terms 1. Allele 2. Amino acid 3. Base 4. Biotechnology 5. Chromosome 6. Clone 7. DNA 8. Electrophoresis 9. Ligation 10. Gene 11. Gel electrophoresis 12. Mutation 13. Polymerase Chain Reaction (PCR) 14. Recombinant 15. Transcription 16. Transformation 17. Translation

6 Nucleic Acids and Nucleotides Nucleic acids are long, slightly acidic molecules originally identified in cell nuclei. Nucleic acids are made up of nucleotides, linked together to form long chains. The nucleotides that make up DNA are shown.

7 Nucleic Acids and Nucleotides DNA s nucleotides are made up of three basic components: a 5- carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base. The nucleotides in a strand of DNA are joined by covalent bonds formed between their sugar and phosphate groups.

8 Chargaff s Rules Erwin Chargaff discovered that the percentages of adenine [A] and thymine [T] bases are almost equal in any sample of DNA. The same thing is true for the other two nucleotides, guanine [G] and cytosine [C]. The observation that [A] = [T] and [G] = [C] became known as one of Chargaff s rules.

9 Franklin s X-Rays In the 1950s, British scientist Rosalind Franklin used a technique called X-ray diffraction to get information about the structure of the DNA molecule. X-ray diffraction revealed an X-shaped pattern showing that the strands in DNA are twisted around each other like the coils of a spring.

10 The Work of Watson and Crick At the same time, James Watson, an American biologist, and Francis Crick, a British physicist, were also trying to understand the structure of DNA. They built three-dimensional models of the molecule. Watson is on the left

11 The Work of Watson and Crick Early in 1953, Watson was shown a copy of Franklin s X-ray pattern. The clues in Franklin s X-ray pattern enabled Watson and Crick to build a model that explained the specific structure and properties of DNA. Watson and Crick s breakthrough model of DNA was a double helix, in which two strands were wound around each other.

12 Antiparallel Strands In the double-helix model, the two strands of DNA are antiparallel they run in opposite directions. This arrangement enables the nitrogenous bases on both strands to come into contact at the center of the molecule.

13 Hydrogen Bonding Watson and Crick discovered that hydrogen bonds could form between certain nitrogenous bases, providing just enough force to hold the two DNA strands together.

14 Base Pairing Watson and Crick s model showed that hydrogen bonds could create a nearly perfect fit between nitrogenous bases along the center of the molecule. This nearly perfect fit between A T and G C nucleotides is known as base pairing, and is illustrated in the figure.