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DNA - PowerPoint PPT Presentation

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DNA
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  1. DNA The BIG show! All animations are from Virtual CellAnimation Collection http://vcell.ndsu.edu/animations/home.htm

  2. Watson and Crick • 1953 the structure of DNA was finally described • Based on Roselind Franklin and Maurice Wilkins’ crystallography of DNA (Wilkins shared in Nobel prize 1962 – Franklin had died) http://www.odec.ca/projects/2007/knig7d2/images/WatsonCrick.jpg

  3. Double Stranded Helix • DNA is comprised of • two strands of nucleic acids - bases • 6 carbon sugar – phosphate backbone • helix – twists around each other, like the stripes of a peppermint stick http://whyfiles.org/034clone/images/dna_molecule.gif

  4. Structure of DNA • Primary • Sequence of base pairs along one strand – ATGC • Secondary • DNA is wrapped around histones • Tertiary • Histones are grouped into bundles • Quaternary • DNA located on pairs of Chromosomes http://employees.csbsju.edu/hjakubowski/classes/ch331/DNA/chromosome.gif

  5. Nucleotides • DNA is made up of subunits which scientists called nucleotides. • Each nucleotide is made up of a sugar, a phosphate and a base. • There are 4 different bases in a DNA molecule: • adenine (a purine) • cytosine (a pyrimidine) • guanine (a purine) • thymine (a pyrimidine) • The number of purine bases equals the number of pyrimidine bases • The number of adenine bases equals the number of thymine bases • The number of guanine bases equals the number of cytosine bases • The basic structure of the DNA molecule is helical, with the bases being stacked on top of each other

  6. What does that mean? • Adenine is hydrogen bonded to Thymine • Guanine is hydrogen bonded to Cytosine • DNA is directional from 5’ to 3’ http://porpax.bio.miami.edu/~cmallery/150/gene/c16x6base-pairs.jpg

  7. Directional? • The DNA is “read” from the 5’ to the 3’ end, just like we read words from left to right • When DNA is replicated, it is read from 5’ to 3’ • The two strands unzip to allow room for replication factors https://eapbiofield.wikispaces.com/file/view/DNA-replication.jpg

  8. Why is that important • Double stranded adds stability to DNA • Easy to find errors in copying or transcribing to RNA or mutations • Easy to find T with a G or C with an A http://www.science.mcmaster.ca/mciars/Doug%20Boreham/Website_July2/Images_forwebsite/prymidine_dimer.jpg

  9. Genes • Areas of DNA have readable sequences which code for genes • Many parts of the genome are “junk DNA” • Genes can have differences in the AT and GC, which form alleles • If not detrimental, the mutation will continue • If advantageous, the allele will become more common

  10. Questions? BJ Shaw Panochthus frenzelianus American Museum of Natural History 2004

  11. DNA to RNA to Protein

  12. Overview • How it works • DNA – double stranded to protect and reduce the mutations • RNA – unstable, and breaks down quickly in the cell

  13. Types of RNA • mRNA (messenger RNA) is transcribed from DNA • tRNA (transfer RNA) is the molecule that carries amino acids • rRNA (ribosomal RNA) reads mRNA and matches tRNA to build the protein in the correct sequence http://www.aps.anl.gov/Science/Highlights/2001/Images/ribomain.gif

  14. Types of RNA • cRNA (catalytic RNA) catalyses many reactions in the cytoplasm of the cell. • snRNA (small nuclear RNA) have various roles in the processingof the other classes of RNA. • snoRNA (small nucleolar RNA) over 100 of them found in the nucleolus where they are involved in several functions including making ribosomes

  15. Amino Acids • Four nucleotides (Adenine, Thymine, Guanine, and Cytosine) translate into 20 different amino acids • If 1 nucleotide = 1 amino acid, only 4 amino acids • If 2 nucleotides = 1 amino acid, then 16 amino acids (still short) • If 3 nucleotides = 1 amino acid, then 64 amino acids (too many) http://www.ccs.k12.in.us/chsTeachers/BYost/Biology%20Notes/translation_files/image007.jpg

  16. Amino Acids • Closer look… • AUG = methionine, the start of the protein sequence • UAA = stop • UAG = stop • UGA = stop • Other codes allow for “wobble” room • For example, serine starts with a UC, and any other nucleotide http://www.ccs.k12.in.us/chsTeachers/BYost/Biology%20Notes/translation_files/image007.jpg

  17. Protein Synthesis • DNA unzips • Similar to replication, DNA is copied (transcription) • Uracil is the molecule that pairs with Adenine rather than Thiamine http://upload.wikimedia.org/wikipedia/commons/5/5e/RNA_polymerase_%281i6h%29.png

  18. Protein Synthesis • mRNA is edited • mRNA is spliced • mRNA exits the nucleus of the cell and is associate with the small subunit of rRNA (a ribosome) for translation • The protein is constructed one amino acid at a time

  19. Proteins • Complex molecules • One of the four major types of molecules found within the cell • DNA, RNA, and lipids are the other three • These comprise the variation found within populations • The amount of melanin will determine the color of the iris – or it is at least 74% responsible http://discovermagazine.com/2007/mar/eye-color-explained/eyes-400.jpg

  20. Questions? BJ Shaw Megatherium americanum Museo de La Plata 2008