DNA Structure

1. DNA Structure Which two scientists constructed the first accurate model of DNA’s structure? Which scientist took crucial X-Ray crystallography photographs of DNA, but did not receive the Nobel Prize like the others?

2. Homework • Discovering DNA packet due Wednesday

3. Objectives • Be able to draw and label a diagram of the molecular structure of DNA, showing the relationships between the six essential molecules that make up DNA: deoxyribose, phosphate, adenine, cytosine, guanine, thymine. • Recognize and know the term for the shape of a DNA molecule.

4. DNA • Deoxyribonucleic acid (DNA) is the “blueprint for the cell” and the “molecule of heredity.” This means that it is the chemical that transmits things from generation to generation. • DNA is just a chemical, made of atoms bonded to each other, like any other molecule. • It is really DNA that gives orders to the cell. The nucleus is just what holds the DNA. • Four of DNA’s 6 chemical parts are nucleic acids. A nucleic acid is another kind of macromolecule, like lipids and carbohydrates.

5. Macromolecules & Cell Parts Genetic material: “Blueprint” for cell Carbon, Nitrogen, Hydrogen

6. DNA is a molecule made up of six chemicals: deoxyribose, phosphate, adenine, guanine, cytosine, and thymine. • Deoxyribose is a sugar. A, C, G, and T are nucleic acids. • Because of the way that these six molecules bond to each other, DNA is in a “twisted ladder” or double helix shape.

7. Nucleic acids = the “rungs” of the ladder • Deoxyribose & phosphate = the “backbone” of the ladder • Each nucleic acid = bonded to one deoxyribose.

8. DNA • Nucleic acids = also called “nitrogenous bases” or just “bases” • Each of the four nucleic acids (A, C, G, and T) is bonded to one deoxyribose and one phosphate on one end. • These three molecules bonded together - nucleic acid, deoxyribose, and phosphate - is called a nucleotide. Nucleotides are what you cut out to make your paper DNA model. • On the other end, a nucleic acid seeks to form a bond with its base pair partner. • A with T, C with G.

9. DNA Problems • Chargaff’s Rule is the rule that A goes with T and C with G. • If a string of DNA is A-T-G-G along one strand, what will be along the other strand? • A-T-G-G

10. DNA Problems • CGGATTATG • GATTACA • AATGCGC

11. DNA Structure • 1. Color your pieces. • 2. Take one pair of scissors and roll of tape for each table. Cut out each of your DNA nucleotides, and then tape them together into a correct ladder structure. Match up the correct bases! • 3. Tape each of your DNA chains together. Then, find another group and tape your chain onto the end of theirs, etc. • 4. When you finish, help another group to cut and tape, or work on homework. • Pay attention to this structure! I may ask you to draw it on a test. And/or I may give you a sequence of base pairs, and ask you to tell me what the other chain’s sequence would be. (ex: “If one side of the chain is ATTGCTAGGCTA, what is the other side?”)

12. Video

14. Chromosomes • DNA doesn’t just float around in pieces. There’s too much of it to fit into the nucleus unless it’s condensed, and it would be too complicated without organization. So it’s organized into chromosomes. • Chromosome = a very long strand of DNA bunched up and tightly wound around proteins.

16. Chromosomes • All the genetic information an organism has is called its genome. • A normal human cell has 46 chromosomes. • If all the chromosomes were strung end-from-end, the human genome would be more than 3 billion base pairs long!

17. DNA Replication • With your table partner, come up with as many reasons as you can think of for why a cell would divide to make a copy of itself.

18. DNA Replication • DNA Replication =

19. DNA Replication • DNA Replication = DNA copying itself. • When a cell grows too large, it must divide. Everything in the cell must copy itself, including DNA. • Recall from the video that James Watson was especially excited when they made their first correct model of DNA, because he realized that it also told them how DNA replication works.

20. DNA Replication • In DNA Replication, DNA “untwists and unzips.” Then, free nucleotides floating around are drawn to their base pair partners, forming new bonds. Thanks to base pairing, DNA makes identical copies of itself. • http://www.youtube.com/watch?v=hfZ8o9D1tus

21. Replication • Each “daughter cell” winds up with identical DNA. • In each new DNA molecule, one strand is from the old DNA, and one strand is new.

22. Mind Map/Concept Map • Rules: • Each concept must be on the map, and no others. • Each concept must be linked at least once. • Each link must make a sentence on its own. • Two concepts can only be linked once. YES: NO: are sold in Stores Shoes serve buy Customers buy Shoes Customers Stores by are sold to

23. Mind Map/Concept Map • Terms: • DNA • Nucleic Acid • Nucleotide • Base Pair • Deoxyribose • Phosphate • Adenine • Cytosine • Guanine • Thymine • Chromosome • Genome • Nucleus

24. Study Guide • Make a study guide for the quiz. Remember that quiz topics are: • The discovery of DNA • DNA structure • DNA organization (chromosome & genome) • DNA replication