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DNA: Structure and Replication

DNA: Structure and Replication. Two Types of Nucleic Acids. Slide # 2. Nucleic Acids : carry the genetic instructions for all life. Discovery of Nucleic Acid. Slide # 3. 1869: Friedrich Miescher discovered nuclein Noticed that nuclein had a lot of phosphate

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DNA: Structure and Replication

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  1. DNA: Structure and Replication

  2. Two Types of Nucleic Acids Slide # 2 Nucleic Acids: carry the genetic instructions for all life

  3. Discovery of Nucleic Acid Slide # 3 • 1869: Friedrich Miescher discovered nuclein • Noticed that nuclein had a lot of phosphate • He found nuclein in every type of cell he studied. Miescher’s lab

  4. Griffith’s Experiment Slide # 4 • 1. 1928: Frederick Griffith • a. Showed that bacteria could be transformed • b. transformation: process in which bacteria can take up the genes of another bacteria and express those genes

  5. Avery’s Experiment Slide # 5 Oswald Avery continued Griffith’s experiment! Avery showed that DNA is the transforming agent!

  6. Hershey and Chase Experiment Slide # 6 • 1. 1952: Hershey & Chase used radioactive markers on viruses • a. showed that virus only injects nucleic acid into bacteria • b. bacteria take up nucleic acid and can express the new genes • c. demonstrated that DNA is the genetic material of the cell

  7. Components of DNA Slide # 7 DNA is made up small, repeating units (monomers) called nucleotides. • Nucleotide has 3 parts: • 1. A phosphate group • 2. A sugar (called deoxyribose) • 3. Nitrogen base (4 different bases) • Adenine “A” • Thymine “T” • Cytosine “C” • Guanine “G” Adenine Guanine Cytosine Thymine Phosphate group Deoxyribose Go to Section:

  8. Chargaff: Discovered Ratios of Nitrogen Bases Slide # 8 • 1940’s: Erwin Chargaff discovered that the % of base “A” was almost equal to the % of base “T” & the percent of base “C” was nearly equal to the % of base “G”– didn’t know why • Also discovered that composition of DNA (% of A, T, C, & G) varies from species to species • Both discoveries gave support that DNA carries the genetic code! Chargaff

  9. Percentage of Bases in Four Organisms Slide # 9 Source of DNA A T G C Streptococcus 29.8 31.6 20.5 18.0 Yeast 31.3 32.9 18.7 17.1 Herring 27.8 27.5 22.2 22.6 Human 30.9 29.4 19.9 19.8 Go to Section:

  10. Rosalind Franklin: The Famous Picture Taker Slide # 10 • 1952: Rosalind Franklin: an expert in x-ray crystallography. • She took the x-ray picture of DNA -- shows DNA is a double helix. • 1958: Franklin died (37 years old)

  11. James Watson & Francis Crick: Puzzle Solvers Slide # 11 • 1953: Discovered the structure of DNA • Described DNA as a doublehelix (twisted ladder) • Sides of ladder are made up of sugar & phosphate groups • Steps of ladder are made up of nitrogen base pairs (A-T & C-G) -- Applied Chargaff’s rules • Base pairs (steps) are held together by weak hydrogen bonds • Sequence (order) of nitrogen bases determines the genetic instructions / “genetic code” of organism. James Watson Francis Crick

  12. DRILL #12 Quote:Whatever you are, be a good one! Abraham Lincoln Agenda: Homework check DNA structure cont. Cell Division notes Warm-up: 1. Which of the following best describes cellular respiration? a. External breathing b. Breakdown of sugar to release energy in cells c. Movement of water from outside the cell to inside the cell. d. Removal of water from a cell 2. Describe the structure and components of a DNA nucleotide.

  13. Knowing the Structure Tells how DNA Replicates Slide # 12 • DNA Replication: makes 2 identical DNA strands by copying the original model • Each new strand contains one old (parent) strand & one new (daughter) strand • DNA replication occurs during cell division – inside the nucleus Parent strand: gray Daughter strand: red

  14. Steps in DNA Replication Slide # 13 • DNA unwinds (DNA Helicase) • DNA polymerase breaks hydrogen bonds that hold nitrogen bases together • DNA ligase hydrogen bond new nitrogen bases onto DNA parent strand • Chargaff’s rules applied: A-T & C-G • Nucleotides added in 5’ to 3’ direction • Sugar-phosphate groups bond to nitrogen bases to complete daughter strand • Result: 2 identical DNA strands each contains 1 parent strand & 1 daughter strand

  15. Steps in DNA Replication Slide # 14 Parent strand Daughter strand Strands are antiparallel

  16. When Does Replication Occur? Slide # 15 • 1. The cell replicates (makes a copy) its DNA right before cell division. • 2. When two new cells are produced in cell division, each new cell needs its own copy of the DNA (identical copy!) • 3. After DNA replication, the cell will divide in half (cell division) and give each new cell a copy of the DNA

  17. Chromosomes Slide # 16 • Fertilized human egg cell has 46 chromosomes • 23 chromosomes in egg cell • 23 chromosomes in sperm cell • Humans have 46 chromosomes in each body cell. • 2. Each cell has millions of base pairs storing our genetic code. • 3. After DNA Replication, each cell has 92 “sister chromatids” • After mitosis, each cell ends up with 46 chromosomes Karyotype of Human chromosomes

  18. Slide # 17 Chromosomes: More than Just DNA Chromosome:coiled DNA & protein “spacers” called histones. Histones keep the chromosome from getting tangled.

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