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The student is expected to: 3F research and describe the history of biology and

Research the history of biology and DNA structure, learn about nucleotides, double helix, base pairing rules, and contributions of scientists like Watson, Crick, Franklin, and Chargaff.

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The student is expected to: 3F research and describe the history of biology and

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  1. The student is expected to: 3F research and describe the history of biology and contributions of scientists; 6A identify components of DNA, and describe how information for specifying the traits of an organism is carried in the DNA; 6B recognize that components that make up the genetic code are common to all organisms

  2. KEY CONCEPT DNA structure is the same in all organisms.

  3. DNA DNA is one of the 4 types of macromolecules known as a nucleic acid. DNA stands for deoxyribonucleic acid.

  4. phosphate group nitrogen-containing base deoxyribose (sugar) DNA is composed of four types of nucleotides. • DNA is made up of a long chain of nucleotides. • Each nucleotide has three parts. • a phosphate group • a deoxyribose sugar • a nitrogen-containing base

  5. The nitrogen containing bases are the only difference in the four nucleotides.

  6. The chain has a direction determined by whether the deoxyribose is right side up, or upside down. The “top” of the molecule will have a phosphate sticking out. It is known as the 5’ end (5 prime).

  7. If there is no phosphate sticking out, it is the 3’ end (3 prime).

  8. Constructing the DNA Polymer 5’ 3’ 3’ 5’

  9. It looks like a twisted ladder. The strands run in opposite directions; called antiparallel (like opposite flows of traffic)

  10. Watson and Crick determined the three-dimensional structure of DNA by building models. • They realized that DNA is a double helix that is made up of a sugar-phosphate backbone on the outside with bases on the inside.

  11. Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin Chargaff. • Franklin’s x-ray images suggested that DNA was a double helix of even width. • Chargaff’s rules stated that A=T and C=G.

  12. Chargaff’s Rules: Erwin Chargaff (1905-2002) discovered that in any DNA sample the amount of guanine is always equal to the amount of cytosine, the amount of adenine was always equal to the amount of thymine. A = T G = C

  13. G C A T Nucleotides always pair in the same way. • The base-pairing rules show how nucleotides always pair up in DNA. • A pairs with T • C pairs with G • Because a pyrimidine (single ring) pairs with a purine (double ring), the helix has a uniform width.

  14. This eventually led to our base pairing rules: Each base pair is made of 1 purine and 1 pyrimidine. 2. Adenine from one strand and thymine from the other always pair together with two hydrogen bonds

  15. 3. guanine on one strand and cytosine on the other strand always bond together with three hydrogen bonds.

  16. covalent bond hydrogen bond • The backbone is connected by covalent bonds. • The bases are connected by hydrogen bonds.

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