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Planners

Planners. MONDAY: Study the “old dead people” from this unit! TUESDAY: QUIZ on DNA structure WEDNESDAY: THURSDAY: FRIDAY: TEST —DNA . DNA Structure. What the heck is DNA made of?. Erwin Chargaff. Biochemist

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Planners

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  1. Planners • MONDAY: Study the “old dead people” from this unit! • TUESDAY: QUIZ on DNA structure • WEDNESDAY: • THURSDAY: • FRIDAY: TEST—DNA

  2. DNA Structure

  3. What the heck is DNA made of?

  4. Erwin Chargaff • Biochemist • Discovered that the amount of A (Adenine) equaled the amount of T (thymine) in ANY DNA sample.

  5. Erwin Chargaff • Also that the amount of G (Guanine) equaled the amount of C (cytosine) in ANY DNA sample. • This idea is called “Chargaff’s Rule”

  6. Rosalind Franklin • First person to “photograph” DNA. • Used an X-Ray machine to take the picture. • Her photograph revealed an “X” shaped pattern.

  7. Rosalind Franklin • This is her famous photograph. • The angle of the “X” shape suggested that there were 2 strands, not 1!

  8. Watson and Crick • At the same time Franklin was taking pictures of DNA, Watson and Crick were trying to make a 3D model of DNA.

  9. Watson and Crick • As soon as Watson saw Franklin’s photograph they figured it out. • They discovered that DNA was actually 2 strands twisted around each other.

  10. Double Helix • A Double Helix looks like a twisted ladder, or a spiral staircase. • The double helix model explains Chargaff’s rule of base pairing and how the two strands of DNA are held together!

  11. Antiparallel • The 2 strands of DNA run in opposite directions. • The base pairs meet in the middle.

  12. Start End Stop End Adenine Thymine Guanine Cytosine Antiparallel Lines Stop End Start End

  13. Hydrogen • The two strands of DNA are held together by hydrogen bonds! • The bonds form between certain base pairs. • Why would you want a WEAK bond to hold together something as important as DNA?

  14. Hydrogen Bonding is happening at the dotted lines!

  15. Watson and Crick showed that hydrogen bonding only happens between certain base pairs… Adenine and Thymine Guanine and Cytosine This perfectly fit between A-T and G-C nucleotides is called base pairing!

  16. Name one scientist who contributed to our understanding of the structure of DNA.

  17. Quiz • What are the letters used to represent the nitrogen bases? • Which base pairs up with (T)? • What kind of chemical bond holds nitrogen bases together? • What kind of sugar is in DNA?

  18. Planners • MONDAY: Homework—DNA Base Pairing and Structure Sheet • TUESDAY: Homework—DNA Replication Sheet • WEDNESDAY: Homework—What is a DNA mutation? • THURSDAY: Quiz • FRIDAY:

  19. Parts of DNA Phosphate Backbone Nitrogen Base Deoxyribose (Sugar) Adenine Thymine Guanine Cytosine

  20. These three molecules make up a NUCLEOTIDE. Many NUCLEOTIDES make up a NUCLEIC ACID.

  21. What are the chemical components of DNA? Phosphate Group, Deoxyribose, Nitrogen Base Pairs—Adenine, Guanine, Thymine, Cytosine

  22. Why are hydrogen bonds essential to the structure of DNA? H-bonds hold the paired bases together. Because the bonds are weak the two strands of DNA are easily separated.

  23. Describe the discoveries that led to the modeling of DNA. Chargaff: (A) = (T) and (G) = (T) Franklin: 2 strands, maybe a spiral? Watson and Crick: Double helix, base pairing

  24. Why did scientists have to use tools other than microscopes to solve the structure of DNA? DNA is too small to be examined with a light microscope—the only microscope available at the time.

  25. Describe Watson and Crick’s Model of the DNA molecule. Two Antiparallel strands that are connected by hydrogen bonds between nitrogenous bases…A = T and G = C

  26. Did Watson and Crick’s model account for the equal amounts of (T) and (A) in DNA? Watson and Crick’s model showed a double helix with (T) and (A) paired together…so, YES.

  27. Sources • http://www.apsnet.org/edcenter/K-12/TeachersGuide/DNA_Easy/Pages/Background.aspx • http://www.nature.com/scitable/topicpage/discovery-of-dna-structure-and-function-watson-397 • http://sites.google.com/site/aninditosen2004/home

  28. What are the 3 parts of a nucleotide? Put your homework on your desk please!

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