Griffith Avery Franklin Watson and Crick

Transcription

1 to. Protein

2 Griffith Avery Franklin Watson and Crick

3 Although Mendel understood that we inherit information, he didn t know how In 1928 Frederick Griffith was studying two forms of bacteria species One form harmless, One form fatal to mice When the fatal form was heat treated and injected into the mice the mice lived The heat killed the deadly strain Although this was important what he did next was more important

4 Griffith next injected the mice with both the heat treated and the harmless bacteria When injected with both bacterium the mice died The harmless bacteria was transformed into deadly bacteria All of the descendants of the transformed bacteria inherited the killer trait

5 Griffith discovered that the substance that was in the heat treated bacteria was still inheritable Griffith s experiments showed that there was a specific heritable factor His experiments opened the door to new research that lead to what we now know

6 After Griffith s work became known, scientists began searching for the transforming factor Oswald Avery was one of those such scientists Avery focused on the transforming factor being either protein or DNA

7 Avery took Griffith s experiment and treated the mixture with protein destroying enzymes It was shown that the deadly bacteria were still growing with the proteins destroyed Next they treated the mixture with DNA destroying enzymes The deadly bacteria did not continue to grow after this treatment

8 Avery showed that by destroying either the protein or the DNA one type of colony would survive and one would die The colony that had DNA left was the one that continued to live This living colony showed that it was DNA that was the inheritable factor and not the proteins

9 Many scientists were skeptical of Avery s findings. Most scientists thought that DNA was too simple to be what caused all of our heritable traits

10 After Avery s experiments a pair of scientists Alfred Hershey and Martha Chase added much support to DNA being the heritable factor They studied Viruses which are just a package of nucleic acids wrapped in proteins Viruses only reproduce by infecting a living cell with it s genetic material Since viruses were even less complex it was either the protein or the DNA that was the genetic material

11 Hershey and Chase conduced an experiment that would show which part of the virus was the genetic material They used a radioactive isotope to label either the DNA or the Protein Radioactive Sulfur made the proteins radioactive Radioactive phosphorous made the DNA radioactive

12 Then they let the virus reproduce They had the sulfur coated proteins reproduce in one experiment and the phosphorous in another Only one experiment showed radioactive reproductive cells.

13 Hershey and Chase were able to show through radioactive cells that DNA was the inheritable factor

14 Once it was identified that DNA was the inheritable factor the next step was to understand what it looked like and how it worked Through betrayal, competition, pictures, and trial and error, the shape and function of DNA were discovered

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16 Rosalind Franklin used X-ray crystallography to take photo s of DNA These photo s gave us the imperative clues to the shape and dimensions of DNA Franklin s work was ultimately stolen and used by her competitors to publish the shape of DNA before her.

17 James Watson and Francis Crick worked to create a correct model of DNA s shape It was only after James Watson was shown Franklin s picture by her disgruntled partner did he get the shape right.

18 Watson and Crick found that: the sugar-phosphate backbone belonged on the outside DNA was in the shape of a double helix the base pairing was based on their size The bases across from each other are held together by hydrogen bonds

19 Once the shape and structure of DNA was identified it was then identified how DNA is used DNA goes through many steps to make what we see One Gene makes one protein

20 Nucleotide - smallest information unit Gene string of nucleotides that specifies a protein Chromosome spooled-up string of genes packaged in a single unit Genome all of the chromosomes of a single organism

21 5-carbon sugar - deoxyribose (DNA) or ribose (RNA) Phosphate One of four nitrogenous bases: adenine (A), guanine (G), cytosine (C), thymine (T) (RNA uracil (U) replaces thymine

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24 Bases of nucleotides match up in pairs A pairs with T G pairs with C

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26 du/molvis/tutorials/ dna/dnapairs.htm

27 DNA TO PROTEIN

28 DNA separates Complementary nucleotides are linked along separated strands

29 Weak bonds Hydrogen bonds Comes apart easily Comes together easily

30 Initiator protein guides unzipper protein (helicase) to correct position on DNA

31 Untwister (topoisomerase ) unwinds the DNA double helix in advance of the unzipper

32 Unzipper separates DNA strands, breaking weak bonds between the nucleotides

33 Builders (polymerases) assemble new DNA strand by joining nucleotides to their matching complements on the exposed strands

34 Straightener s (singlestrand DNA binding proteins) keep single strand of DNA from tangling

35 Phosphate bond energy from the new nucleotides is used to make the new bonds

36 Leading (top) strand is built continuously as the builder follows behind the unzipper, but the Lagging (lower) strand builds in the opposite direction

37 Lagging (lower) builder makes a loop with the DNA strand and builds in opposite direction

38 nce.wiley.com:8100/l egacy/college/boyer/ /structur e/dna/dna.htm u/molvis/tutorials/dn a/dnapairs.htm manipulate DNA

39 Built in small sections Sections linked by enzyme ligase

40 Erasers (Repair Nuclease): find poorly matched or damaged nucleotides and cut them out

41 Builders (Polymerase): fill gaps using other DNA strand as a guide

42 Stitchers (Ligase): uses ATP to restore continuity of backbone of repaired strand

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