DNA and DNA Replication - DOC

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					                         DNA and DNA Replication

   DNA
      o Nucleic Acid
      o Information stored controls all cell activity & determines genetic
        characteristics of the cell & organism
      o Each cell contains DNA
      o Made of 2 strands with 1000s of linked nucleotides
             Nucleotides
                     Consist of phosphate group
                     Deoxiribose (5 carbon sugar)
                     Nitrogen base (one of 4)
                            o Adenine
                            o Thymine
                            o Cytosine
                            o Guanine
                     Attached in specific way to form a double helix
                            o A–T
                            o C–G
      o Information stored in DNA determines the sequence of amino acids in
        proteins, controls what proteins are made
      o Each individual has unique genetic information in their DNA that came
        from parents during sexual reproduction

   DNA & Chromosomes
      o Genes are small particle on chromosomes
      o Each chromosome contains a continuous sequence of DNA
      o Watson & Crick –1953
             Proposed double helix shape
             2 strands are complementary because of their molecular shape
             Chemical bond between bases is weak (hydrogen bond) & when
               broken apart 2 separate complementary strands result

   DNA Replication
      o Process of copying DNA
      o Strands separate by enzymes called helicases
      o Each old strand serves as a pattern for formation of a new complementary
         strand
      o DNA polymerases (enzymes) bind to separated chains and move along
         assembling new chains
      o Occurs simultaneously along DNA strand
      o Results in 2 identical double strands of DNA, each exactly like the
         original strand
   RNA
      o Single chain of nucleotides with a different sugar (ribose)
      o Carries information from chromosomes in nucleus to ribosomes in the
        cytoplasm
      o Thymine is replaced with a similar base called Uracil
             A–U
             C–G
      o Synthesized by copying one of the complementary DNA strands
      o 3 types
             rRNA (ribosomal): globular form, makes up ribosomes along with
                proteins
             mRNA (messenger): carries DNA message from nucleus to ribosomes
                in cytoplasm
             tRNA (transfer): carries amino acids to ribosomes

       o Transcription (How RNA uses DNA to copy itself)
             Sends enzyme (RNA polymerase) to “unzip” the needed DNA
                sequence
             mRNA bonds to strand like in DNA replication to make a copy
                     EX:
                     G–C
                     T–A
                     A–U
                     A–U
                     G–C
                     C–G
       o Translation
             mRNA has a set of “instructions” to take to ribosomes
                     Instructions for what?
                          o Ribosomes make proteins, DNA is responsible for
                              telling them how using mRNA
                          o Analogy:
                                    Workers = ribosomes
                                    DNA = boss
                                    mRNA = supervisor
                          o Each letter in DNA is like a sentence written in secret
                              code (written in mRNA)
                          o Code must spell out arrangement of one of 20 amino
                              acids
                                    Combinations of 3 to adequately cover all 20
                                       amino acids
                                           Called codons or triplets
      o Once mRNA comes back to ribosome with the code,
           each codon tells tRNA (postal service) which amino
           acid to bring along to ribosome
      o Amino acids are attached one at a time to end of a
           growing chain (assembly line)
      o Final product is a protein
                Protein synthesis takes place on/in ribosomes in
                   cytoplasm
   Mutation
       Point-where one base is changed.
       Frame-shift-where one base is deleted
       Translocation-two bases switch places
       Any can occur at various places. Depending on where,
           have varying degrees of harmfulness