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The Secret Code. Genes Genes are known to: –Carry information from one generation to the next. –Put that information to work by determining the heritable.

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Presentation on theme: "The Secret Code. Genes Genes are known to: –Carry information from one generation to the next. –Put that information to work by determining the heritable."— Presentation transcript:

1 The Secret Code

2 Genes Genes are known to: –Carry information from one generation to the next. –Put that information to work by determining the heritable characteristics of organisms. –Be easily copied, because all of a cell’s genetic information is replicated every time a cell divides.

3 DNA RNA Protein Scientists call this the: Central Dogma of Molecular Biology!

4 How do we know that all of our genetic information comes from DNA? Thanks to many scientists and many experiments over the last ≈ 80 years. Let’s take a look…….

5 Griffith’s Experiment with Pneumonia in 1928 and the accidental discovery of Transformation Frederick Griffiths was a bacteriologist studying pneumonia He discovered two types of bacteria: –Smooth colonies –Rough colonies CONCLUSION: The smooth colonies must carry the disease!

6 Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation When heat was applied to the deadly smooth type… And injected into a mouse… The mouse lived!

7 Griffith injected the heat-killed type and the non-deadly rough type of bacteria. The bacteria “transformed” itself from the heated non-deadly type to the deadly type. Griffith’s Experiment with Pneumonia and the accidental discovery of Transformation

8 In 1944: Avery, McCarty, and MacLeod Repeated Griffith’s Experiment Oswald Avery Maclyn McCarty Colin MacLeod

9 Avery, McCarty, and MacLeod Added the non-deadly Rough Type of Bacteria to the Heat-Killed Smooth TypeCarbohydratesLipidsProteinsRNADNA To the mixture, they added enzymes that destroyed…

10 S-Type Carbohydrates Destroyed S-Type Lipids Destroyed S-Type Proteins Destroyed S-Type RNA Destroyed S-Type DNA Destroyed Conclusion: DNA was the transforming factor!

11 The Hershey-Chase Experiment: 1952 Alfred Hershey & Martha Chase worked with a bacteriophage: A virus that invades bacteria. It consists of a DNA core and a protein coat DNA Protein coat

12 Protein coats of bacteriophages labeled with Sulfur-35 DNA of bacteriophages labeled with Phosphorus-32 Bacterium Bacterium Phage Phage 1.Hershey and Chase mixed the radioactively-labeled viruses with the bacteria The viruses infect the bacterial cells.

13 Protein coats of bacteriophages labeled with Sulfur-35 DNA of bacteriophages labeled with Phosphorus-32 2.Separated the viruses from the bacteria by agitating the virus- bacteria mixture in a blender

14 Protein coats of bacteriophages labeled with Sulfur-35 DNA of bacteriophages labeled with Phosphorus-32 3.Centrifuged the mixture so that the bacteria would form a pellet at the bottom of the test tube 4.Measured the radioactivity in the pellet and in the liquid

15 The Hershey-Chase results reinforced the Avery, McCarty, and MacLeod conclusion: DNA carries the genetic code! However, there were still important details to uncover…

16 How did DNA: 1. Store information? 2. Duplicate itself easily? These questions would be answered by discovering DNA’s structure

17 The Race to Discover DNA’s Structure 1950 Chargaff’s Rule: Equal amounts of Adenine and Thymine, and equal amounts of Guanine and Cytosine Erwin Chargaff Why do you think the bases match up this way? Purine + Purine = Too wide Pyrimidine + Pyrimidine = Too Narrow Purine + Pyrimidine = Perfect Fit from X-ray data

18 The Race to Discover DNA’s Structure Maurice Wilkins Rosalind Franklin X-Ray diffraction image of DNA taken by Franklin in 1951

19 The Race to Discover DNA’s Structure James Watson Francis Crick 1953 Compiled data from previous scientists to build a double-helical model of DNA

20 DNA Deoxyribonucleic Acid (polymer) A long molecule made up of units (monomers) called nucleotides. –Three components: 5-carbon sugar: Deoxyribose A phosphate group A nitrogenous base Nucleotide

21 DNA Structure Called a double helix –Backbone (sides) : 5-carbon sugar and phosphate groups –Rungs: nitrogenous bases held together with hydrogen bonds

22 Nitrogenous bases Our alphabet has 26 letters –Can create many different words  many different sentences  billions of different books of information. DNA alphabet has 4 letters –A, T, C, and G –Create 3 letter words  Amino acids  proteins  billions of different organisms

23 Nitrogenous bases Purines: –Adenine –Guanine Pyrimidines: –Thymine –Cytosine

24 DNA Replication The double helix did explain how DNA copies itself We will study this process, DNA replication, in more detail

25 How does DNA replicate? ConservativeSemi-ConservativeDispersive Hypotheses:

26 1.Bacteria cultured in medium containing a heavy isotope of Nitrogen ( 15 N) Meselson-Stahl Experiment

27 2.Bacteria transferred to a medium containing elemental Nitrogen ( 14 N) Meselson-Stahl Experiment

28 3.DNA sample centrifuged after First replication

29 Meselson-Stahl Experiment 4.DNA sample centrifuged after Second replication

30 DNA Replication The “parent” molecule has two complementary strands of DNA. Each is base paired by hydrogen bonding with its specific partner (Chargaff’s rule): A with T G with C

31 DNA Unzips The first step in replication is the separation of the two strands. An enzyme called DNA helicase unzips DNA

32 New nucleotides added Each parental strand now serves as a template that determines the order of the bases along a new complementary strand. an enzyme called DNA polymerase adds the bases

33 Gaps are closed The nucleotides are connected to form the sugar- phosphate backbones of the new strands. DNA ligase Each “daughter” DNA molecule consists of one parental strand and one new strand….semi-conservative

34 Reviewing DNA Replication And One more…..And One more And another…

35 Here are some interesting Facts! A single strand of DNA (one chromosome) is about 2 inches long when uncoiled. Each human cell contains 46 chromosomes (6 to 9 feet of DNA) Your body contains trillion of cells. All of your DNA (when uncoiled and tied together) could make about 6000 trips from the Earth to the Moon.

36 A few more cool things about DNA It takes about 8 hours for one of your cells to copy all of its DNA. Our entire DNA sequence is called a Genome…and there is an estimated 3,000,000,000 DNA bases This would take up about 3GB of storage If you could type 60 wpm, 8 hours/day…it would take you 50 years to type this. 99.9% of our DNA is the same…it is the 0.01% that makes you who you are!


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