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Biology

Biology. DNA & the Language of Life. Genes are Made of DNA. Fredrick Griffith (1928) studied pneumonia strains (one was harmless while the other was pathogenic , or disease-causing) Made non-harmful strains harmful ( transformed ) Discovered the ‘transforming agent’ was genetic material

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Biology

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  1. Biology DNA & the Language of Life

  2. Genes are Made of DNA • Fredrick Griffith (1928) studied pneumonia strains (one was harmless while the other waspathogenic, or disease-causing) • Made non-harmful strains harmful (transformed) • Discovered the‘transforming agent’ was genetic material • Oswald Avery (1944) confirmed that the genetic material was DNA http://www.google.com/imgres

  3. Alfred Hershey & Martha Chase performed the‘blender experiments’ using a virus (specifically abacteriophage, or virus that infects a bacteria), bacteria, and radioactively labeled probes. • They concluded that DNA was the genetic material. http://www.google.com/imgres

  4. Structure of DNA Structure determines function. • DNA is made up of nucleotides. • A nucleotide is made up of a 3-carbon sugar called adeoxyribose, a phosphate group (PO3) and a nitrogenous base. http://www.google.com/imgres

  5. There are 4 nitrogenous bases in DNA: Adenine (A), Guanine (G), Thymine (T), and Cytosine (C). • A & G arepurinesand are largerthan T & C which arepyrimidines. http://www.google.com/imgres

  6. Edwin Chargaff (1950’s) discovered that in different species there is always an equal number of A’s and T’s and an equal number of C’s and G’s. • These findings are Chargaff’s Rules. • Adenine matches with Thymine and Cytosine matches with Guanine. http://www.google.com/imgres

  7. A purine matches with a pyrimidine. (a large base matches with a small base, making DNA have a uniform width throughout). • Maurice Wilkins and Rosalind Franklin (1952) used x-raysto photo DNA & discovered that DNA has a spiral shape. • Unfortunately, this x-ray was taken by another scientist, James Watson who realized what the x-ray revealed. http://kentsimmons.uwinnipeg.ca/cm1504/Image265.gif

  8. James Watson and Francis Crick (1953) published their results (and received the Nobel Prize). • They received credit for discovering the shape of DNA. • DNA is double stranded & adouble helix (or twisted ladder). • This double helix is formed by 2 strands of nucleotides. • Each strand is composed of nucleotides: the sugar and phosphate bind to each other to form the “backbone” of the ladder while the nitrogenous bases form the “rungs”. • Each rung is formed with 1 purine bonded with 1 pyrimidine (A-T or C-G). http://www.flyfishingdevon.co.uk/salmon/year3/psy339evolutionarypsychologyroots/watson-crick-dna.jpg

  9. DNA Replication: This is DNA copying itself. This occursduring S phase (synthesis) of Interphase. What happens? • DNA unwinds (unzips): enzymes open the base pairs and hold the double helix apart. • EachDNA strand acts as a template for DNA replication for a new complimentary strand http://www.google.com/imgres

  10. Nucleotides join the original strand 1 at a time • DNA polymerase is the enzyme responsible for the base-pair matching • This is called semi-conservative replicationbecause the new DNA that results has 1 old strand of DNA and 1 new strand of DNA. Watson & Crick hypothesized this as well. http://www.google.com/imgres

  11. http://library.thinkquest.org/04apr/00217/images/content/74-Summary-DNA-Replication.jpghttp://library.thinkquest.org/04apr/00217/images/content/74-Summary-DNA-Replication.jpg

  12. Gene Protein • George Beadle & Edward Tatum hypothesized ‘one gene-one enzyme’ (based on their work w/ bread mold Neurospora crassa). • From this hypothesis, it has been discovered that many genes code for polypeptides (but they are specific): one gene-one polypeptide (part of a protein)

  13. From Genotype to Phenotype • Protein Synthesisisthe production of a protein. • This istaking the organism’sgenotype (genetic makeup) and translating into the phenotype (the physical traits). • DNA is made up of nucleotides (bases). • Thebases make up a gene. • Genes code for the sequence of amino acids (a.a.). • A.A. code for proteins. • Therefore, DNA is a template for making proteins. • An expressed geneis a gene that codes for a protein that is synthesized. (exon) There are 2 types of nucleic acids: DNA and RNA. • RNA= ribonucleic acid. • RNA differs from DNA

  14. http://images1.clinicaltools.com/images/gene/dna_versus_rna_reversed.jpghttp://images1.clinicaltools.com/images/gene/dna_versus_rna_reversed.jpg

  15. RNA • Is single stranded • Contains uracil (U) instead of thyamine (T) • Has a ribose instead of a deoxyribose There are 3 types of RNA: • mRNAismessenger RNA • tRNAis transfer RNA • rRNAisribosomal RNA

  16. Types of RNA: tRNA (Contains rRNA) http://publications.nigms.nih.gov/thenewgenetics/images/ch1_trans.jpg

  17. Protein Synthesis occurs in 2 stages: • Transcription: • DNA is copied • RNA is synthesized or transcribed • This occurs within the nucleus http://biology.unm.edu/ccouncil/Biology_124/Images/transcription.gif

  18. What happens during transcription? • RNA polymerase(enzyme that is responsible for RNA synthesis) separates the DNA double helix & matches RNA bases with 1 DNA template only. • This isspecifically making mRNA. • Instead of T, U is inserted. (U binds with A, C binds with G) • Only 1 RNA strand is made. http://www.google.com/imgres

  19. In prokaryotes, mRNA goes directly to the ribosome (there is no nucleus). • In eukaryotes, mRNA isspliced. • Splicingis when noncoding regions calledintrons(junk DNA)are removed and coding regions calledexonsare sealed together. • Both introns and exons are copied during transcription. • After splicing, mRNA leaves the nucleus and finds a ribosome. http://faculty.uca.edu/~johnc/RNA%20splicing.gif

  20. 2. Translation: • This is when nucleic acids are changed, or translated, into the language of proteins (amino acids). • Thisinvolves mRNA, rRNA, and tRNA. • Itoccurs on a ribosome(either free or attached to the ER, depending on where the protein is going).

  21. Translation: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Translation.gif

  22. What happens during translation? • mRNA attaches to a ribosome. • A tRNA molecule “transfers” or brings over an a.a. forming an amino acid chain; With each additional a.a. the chain grows longer. • tRNA brings the correct a.a. over based on the complementary codons & anticodons (base sequences) http://www.google.com/imgres

  23. acodonis a base sequence on the mRNA strand. This codes for a specific a.a. • Ananticodonis 3 bases found on tRNA that match the codon. Example: • Codon= GCU on mRNA (codes for alanine, an a.a.) • Anticodon= CGA on tRNA http://www.google.com/imgres

  24. tRNA wil ultimately be translated into amino acids. 20 amino acids & 64 codons 3 stop codons (UAA, UGA, UAG) & 1 start codon (AUG) which also codes for methinionine (met) The Triplet Code http://repository.uwlax.edu/~Bob/assets/Code.jpg

  25. Mutations: Changes in Chromosomes • Proteins have various functions:they may act within the cell OR serve a purpose outside of the cell. They may be activates or repressors(turning genes on or off). • Amutationis a random change in the DNA (sequence of nucleotides). • This can bechromosomal mutations(which involve entire chromosomes) orgene mutations(which involve individual genes). • Amutagenis an environment factor that causes a DNA mutation, like radiation and chemicals. • Acarcinogenis a cancer causing agent (this is also a mutagen). • These can betars in cigarette smoke, UV radiation, and other chemicals.

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