1. DNADNA: The Blueprint of Life History Structure & Replication

2. History Mendel’s paper was published 1866 By the 1900’s scientists were aware that proteins and DNA were found in the nucleus –DNA discovered by Freidrich Meischer (1869); named it nuclein However, the structure of DNA was not known and proteins were thought to be the hereditary material

3. Fredrick Griffith (1928) conducted experiments with virulent (harmful) and nonvirulent (harmless) strains of pneumonia bacteria Conclusion: Transformation occurred. The harmless strain had been changed into the disease causing-strain. –He hypothesized that a “factor” was transferred from one to the other

4. Griffith’s Experiment

5. Oswald Avery and group of scientists (1944) repeated Griffith’s work to determine which molecule caused transformation –Destroyed proteins, lipids, carbohydrates, RNA and DNA and tested for transformation –No transformation only when DNA was not present Conclusion: DNA stores and transmits genetic information

6. Alfred Hershey and Martha Chase (1952) experimented with bacteriophages (viruses that infect bacteria) –Hershey and Chase wanted to determine if it was the protein coat or the DNA that entered the infected cell –Used radioactive isotopes and tested bacteria for radioactivity Conclusion: genetic material was DNA, not protein

8. Erwin Chargaff (1950’s) discovered that in a DNA sample, the percentages of guanine and cytosine are almost equal, and adenine and thymine are almost equal Conclusion: Chargaff’s Rule: A = T and C = G

9. Rosalind Franklin (1950’s) used X-ray diffraction to learn about DNA structure –Showed DNA strands were twisted like a helix –Suggested structure contained two strands –Suggested nitrogen bases are near the center

10. James Watson and Francis Crick (1953) were trying to understand structure by building 3- D models –After seeing Franklin’s picture, they built a model that explained how DNA could carry information and be copied –Model included two strands in a double helix

11. DNA Structure Polymer made up of nucleotides 3 basic nucleotide components –5-carbon sugar deoxyribose –Phosphate group –Nitrogen base Adenine Thymine Cytosine Guanine

12. Think of DNA like a twisted ladder… –The sides consist of sugar and phosphate groups bonded together –The rungs or steps consist of base pairs held together by hydrogen bonds –Strands run in opposite directions (antiparallel)

13. Nitrogen Bases Purines – double rings –Include adenine (A) and guanine (G) Pyrimidines – single ring –Include thymine (T) and cytosine (C) Base Pairs –A always pairs with T –C always pairs with G The order of these base pairs is what codes for making proteins

15. DNA and Chromosomes Remember, genes are segments of DNA and are found on chromosomes Most of the time DNA is found as chromatin, which is DNA tightly coiled around proteins called histones (together called a nucleosome) This condenses further to see visible chromosome structure

17. DNA Replication DNA makes copies of itself so that cells can divide –Important for growth and reproduction –Occurs in the S phase of interphase Considered semi-conservative: when a new copy is made, half of the old strand stays with a new strand –Helps reduce copy errors

18. Semi-conservative

19. Overview of Replication DNA molecule separates into two strands Each strand serves as a template for a new strand Two new complementary strands are formed following the rules of base pairing –Rapid and accurate; only about 1 in a billion are incorrectly paired

20. Replication Requires ATP (energy) and the help of many enzymes –DNA Helicase: uncoils and “unzips” DNA strands by breaking hydrogen bonds between bases –DNA Polymerase: adds new nucleotides to the original strand; also proofreads for errors –DNA Ligase: helps join Okazaki fragments on the lagging strand –Nucleases – remove incorrect bases

21. Steps of Replication Begins at special sites called origins of replication –Two strands open and separate making a replication fork

22. DNA polymerase moves along the strands, adding complementary bases and proofreading as it goes. Always builds from 5’ end to 3’ end (on new strand) –This has to do with the carbons in deoxyribose –The two strands run opposite directions of each other

23. On one side, the leading strand, DNA polymerase moves along continuously adding bases –Built toward replication fork in one long strand On the other side, the lagging strand, DNA polymerase adds the bases in groups, creating Okazaki fragments –Built moving away from the replication fork and is made in sections This is due to following the 5’ to 3’ rule.

25. Once the complementary base pairs are added and the strand is complete, you now have two new strands of DNA. Remember, each pairs with an original strand Helicase recoils the two to make two identical DNA molecules

27. 27 DNA by the Numbers Each cell has about 2 m of DNA. The average human has 75 trillion cells. The average human has enough DNA to go from the earth to the sun more than 400 times. –The earth is 150 billion m or 93 million miles from the sun. DNA has a diameter of only 0.000000002 m.