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DNA The BIG show! All animations are from Virtual CellAnimation Collection http://vcell.ndsu.edu/animations/home.htm 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 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 Structure of DNA Primary Secondary DNA is wrapped around histones Tertiary Sequence of base pairs along one strand – ATGC Histones are grouped into bundles Quaternary DNA located on pairs of Chromosomes http://employees.csbsju.edu/hjakubowski/classes/ch331/DNA/chromosome.gif 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 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 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 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 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 Questions? BJ Shaw Panochthus frenzelianus American Museum of Natural History 2004 DNA to RNA to Protein Overview How it works DNA – double stranded to protect and reduce the mutations RNA – unstable, and breaks down quickly in the cell 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 Types of RNA cRNA (catalytic RNA) catalyses many reactions in the cytoplasm of the cell. snRNA (small nuclear RNA) have various roles in the processing of 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 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 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 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 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 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 Questions? BJ Shaw Megatherium americanum Museo de La Plata 2008