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DNA

Explore the foundations of DNA discovery, including pivotal experiments by Griffith and others, the structure of DNA, replication process, and pivotal figures like Avery, Hershey, and Chase. Understand the essential role of DNA in genetic inheritance.

hyatt-jensen
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DNA

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  1. DNA Chapter 10

  2. DNA • Holds our genetic information • Like a library • Important for mitosis to occur • Biologists had to discover the chemical nature of DNA to determine that it is responsible for our genetic information

  3. Griffith and Transformation • Transformation: when a strain of bacteria is changed by a gene or genes from another bacteria • Experiment • Inject mice with bacteria S.pneumoniae • Smooth colonies = virulent (disease causing) • Rough colonies = harmless bacteria

  4. Griffith and Transformation • If the virulent colonies were killed with heat & mixed with harmless bacteria, the harmless bacteria get transformed into virulent bacteria • Some factor of the harmless bacteria was transformed to become virulent

  5. Avery and DNA • Wanted to repeat Griffith’s experiment • Treated heat killed virulent bacteria with enzymes • Used two enzymes that destroyed proteins, and RNA • Another enzyme destroyed ONLY DNA (nucleic acids) Lethal Virus

  6. Avery and DNA Results • Results: bacteria treated with DNA destroying enzyme did not transform harmless bacteria into virulent bacteria • It must be the DNA that stores the genetic information from one generation to the next Lethal Virus Lethal Lethal Non Lethal

  7. Hershey-Chase • Bacteriophage: a virus that infects bacteria ONLY • Scientists wanted to see what gets injected into a bacteria to cause infection • Used a radioactive marker DNA and protein

  8. Hershey Chase Results • After infection, the bacteria that had radioactive marker on DNA showed that it is the DNA that is inserted into the bacteria • Results: geneticmaterial of the bacteriophage was DNA and not protein

  9. DNA Structure • Rosalind Franklin • Scientist that worked with X-raydiffraction • Used X-rays on a portion of DNA and the results showed an X pattern

  10. DNA Structure • Watson & Crick • Scientists that were able to figure out what Rosalind’s X-ray patternmeant • Result: DNA has a doublehelix pattern where the nitrogenous bases face each other in the middle

  11. DNA Structure • DNA has a double helix pattern • The sides of the ladder are the sugar and phosphate • Rungs of the ladder are the nitrogenousbases paired up • The bond between two nitrogenous bases is a hydrogen bond

  12. DNA Structure • Backbone of DNA is the sugar and phosphate • Nitrogenous bases stick out of side to form latter rungs • These bases are repeated in a pattern that form our genetic code

  13. DNA Structure • Monomer of DNA is a nucleotide • Phosphorous group • 5-carbon sugar • Nitrogenous base • 4 Nitrogenous bases in DNA • Adenine • Guanine • Thymine • Cytosine

  14. DNA Structure • Chargaff’s Rule • Scientist that discovered a peculiar trend between the 4 bases • Same percentage of Adenine as Thymine • Same percentage of Guanine as Cytosine • Adenine binds to Thymine • Guanine binds to Cytosine

  15. DNA Replication • Process by which DNA is copied in a cell before division • Each strand of DNA is needed to be a template for a new strand of DNA to be produced • Since you can use one strand to make the other side, they are said to be complementary

  16. Replicating DNA • Step 1: DNA molecules separates into two strands with help from enzyme named helicase • Breaks hydrogen bonds between bases • Creates a replicationfork

  17. Replicating DNA • Step 2: Enzyme named DNA polymeraseadds new nucleotides to other side of template strand • This forms new hydrogen bonds DNA Polymerase can only move in one direction (3’-5’) so you have one strand that leads and one that lags To join the gaps between lagging strands and enzyme (ligase) come and binds them

  18. Replicating DNA • Step 3: Once the DNA is replicated, the DNA polymerase releases

  19. How Replication Occurs • Enzymes help make new strands of DNA • Helicase “unzips” the DNA, separating the base pairs • DNApolymerase adds new bases to pair up with the template • This enzyme also proofreads to make sure everything matches • What would be the matching bases to the part of DNA shown below?

  20. Eukaryotes vs. Prokaryotes • Eukaryotes • Long rod shaped chromosomes • Replication starts in certain points on the chromosome • Try to be as effective and time efficient • Prokaryotes • Circular chromosome • Replication begins in one place • Ends once the DNA polymerase meets its starting point • Very fast

  21. Protein Synthesis • Two parts process to make a protein from a segment of DNA • Part one: Transcription • DNA RNA • Part two: Translation • RNA  Protein

  22. RNA • Made of nucleotides • Three differences between DNA & RNA • Sugar • DNA = deoxyribose sugar • RNA = ribose sugar • RNA is single stranded • RNA uses Uracil instead of Thymine to bond with Adenine

  23. RNA • Three types of RNA • mRNA • Messenger RNA • rRNA • Ribosomal RNA • tRNA • Transfer RNA

  24. RNA • Messenger RNA • This is a copy of complimentary strand of DNA • Eventually will code for a protein to be made

  25. RNA • Ribosomal RNA • RNA found in ribosomes (organelles in the cell)

  26. RNA • Transfer RNA • Help produce a protein from mRNA • Brings aminoacids (monomer of protein) to ribosome to bond them together and make a whole protein

  27. Transcription • Taking DNA and making an RNA copy • Step 1: RNApolymerase binds to a promoter and unwinds the strands • Step 2: RNA polymerase adds free RNA nucleotides that are complimentary to DNA strands • Once this is made it is called pre-mRNA • Step 3: RNA polymerase reaches a termination signal and releases

  28. RNA Editing • Pre-mRNA is a roughdraft to the final copy of mRNA • Some parts of pre-mRNA are not needed to make a certain protein • These unnecessary parts are called introns • Introns get cut out of pre-mRNA • Before leaving the nucleus, mRNA needs to get a 5’ cap and poly A tail to finalize the RNA strand

  29. The Genetic Code • Proteins are made of aminoacids • There are 20 amino acids • In order to make a protein from a strand of mRNA, the mRNA is read in a 3 letter sequence called codons

  30. The Genetic Code • Each three letter codon represents an amino acid • DNA = AGCGTGCCAATT • RNA = UCG-CAC-GGU-UAA • Amino acids = Ser-His-Gly-STOP

  31. The Genetic Code • Each three letter codon represents an amino acid • DNA = TACCGTCCGGTCATC • RNA = AUG-GCA-GGC-CAG-UAG • Amino acids = Met-Ala-Gly-Gln-STOP

  32. Translation • Taking mRNA and making a protein • Occurs in the cytoplasm on a ribosome • Step 1: 2 ribosomal subunits bind to mRNA and a tRNA molecule. The tRNA molecule matches to the codon of the mRNA sequence • The first amino acid is always Methionine • If mRNA = AUG, then tRNA = UAC • The tRNA has the anti-codon

  33. Translation • Step 2-3: As tRNA brings new aminoacids to the ribosome, past ones break off leaving just amino acids bonded to each other • Step 4: This continues until one of the three STOPcodons is met • Step 5: ribosomal units break down and the amino acid strand goes through proteinfolding

  34. The Human Genome • The entire genome sequence of a human • 3.2 billion base pairs in our 23 chromosomes • We now need to learn what each of these sequences code for • This will help with curing diseases and prevention of others

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