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Unit 5 Molecular Genetics DNA and RNA I. DNA- deoxyribonucleic acid A. History of DNA as Genetic Material “code of life” 1. Griffith and Transformation a. Frederick Griffith made discovery while investigating bacteria known to produce pneumonia b. Griffith isolated two different strains of bacteria 1). Disease causing strain- had (S) smooth edges. When injected into mice caused pneumonia. 2). Harmless strain- grew with (R) rough edges. 3). When disease causing bacteria heatedmice survived when injected 4). Mixed the heated-killed bacteria and harmless ones. When injected caused pneumonia. Concluded that one strain had been changed into another. Called transformation (another organism takes up outside DNA.). Chapter 12 Molecular Genetics 12.1 DNA: The Genetic Material Avery Identified the molecule that transformed the R strain of bacteria into the S strain Concluded that when the S cells were killed, DNA was released R bacteria incorporated this DNA into their cells and changed into S cells. Concluded that DNA carries the genetic code Chapter 12 Molecular Genetics 12.1 DNA: The Genetic Material Hershey and Chase Showed conclusively that DNA was molecule that carried genetic code. Studied viruses known as Bacteriophages (virus that infects bacteria) Bacteriophage Used different radioactive markers to label DNA and proteins of bacteriophages Chapter 12 Molecular Genetics 12.1 DNA: The Genetic Material DNA Structure Nucleotides Consist of a five-carbon sugar a phosphate group a nitrogenous base Base Groupings Purines (Double ringed) 1. Adenine 2. Guanine Pyrimidines (Single ringed) 1. Cytosine 2. Thymine Backbone of DNA chain formed by sugar and phosphate groups of nucleotides sugar phosphate Chargaff’s Rule- ratio of guanine:cytosine and adenine:thymine are equal A=T and G=C Chapter 12 Molecular Genetics 12.1 DNA: The Genetic Material X-ray Diffraction 1950’s Rosalind Franklin used X-ray diffraction to study structure of DNA molecule. Concluded structure was coiled like a spring (helix) X-ray diffraction data helped solve the structure of DNA X-ray Diffraction cont’d… Indicated that DNA was a double helix Chapter 12 Molecular Genetics 12.1 DNA: The Genetic Material Watson and Crick After looking at Franklin and Wilkin’s work, Watson and Crick constructed a model of DNA molecule (1953) Chapter 12 Molecular Genetics 12.1 DNA: The Genetic Material DNA Structure DNA often is compared to a twisted ladder. Rails of the ladder are represented by the alternating deoxyribose and phosphate. The pairs of bases (cytosine–guanine or thymine–adenine) form the steps. Chapter 12 Molecular Genetics 12.1 DNA: The Genetic Material Chromosome Structure DNA coils around histones to form nucleosomes, which coil to form chromatin fibers. Quick Molecular Genetic Terminology • • • • Replication= DNA DNA Transcription= DNA RNA Translation= RNA Amino Acids Polypeptide= Chain of amino acids • Adenine, cytosine, & guanine= DNA & RNA • Thymine= DNA Only • Uracil= RNA Only Chapter 12 Molecular Genetics 12.2 Replication of DNA Replication Parental strands of DNA separate, serve as templates, and produce DNA molecules that have one strand of parental DNA and one strand of new DNA. Chapter 12 Molecular Genetics 12.2 Replication of DNA Unwinding DNA helicase, an enzyme, is responsible for unwinding and unzipping the double helix. RNA primase adds a short segment of RNA, called an RNA primer, on each DNA strand. Chapter 12 Molecular Genetics 12.2 Replication of DNA Joining DNA polymerase removes the RNA primer and fills in the place with DNA nucleotides. DNA ligase links the two sections. Chapter 12 Molecular Genetics 12.2 Replication of DNA Comparing DNA in Eukaryotes and Prokaryotes Eukaryotic DNA located in cells nucleus in form of a number of chromosomes In prokaryotes, the circular DNA strand is opened at one origin of replication. Chapter 12 Molecular Genetics 12.3 DNA, RNA, and Protein Central Dogma: DNA makes RNA makes protein RNA Contains the sugar ribose and the base uracil Usually is single stranded Chapter 12 Molecular Genetics 12.3 DNA, RNA, and Protein Messenger RNA (mRNA) Strands of RNA nucleotides that are complementary to one strand of DNA Ribosomal RNA (rRNA) Helps join the mRNA codons to the tRNA anticodons in the ribosome Transfer RNA (tRNA) Transport amino acids to the ribosome Chapter 12 Molecular Genetics 12.3 DNA, RNA, and Protein Chapter 12 Molecular Genetics 12.3 DNA, RNA, and Protein Transcription DNA to mRNA DNA is unzipped in the nucleus and RNA polymerase binds to a specific section where an mRNA will be synthesized. Animation Chapter 12 Molecular Genetics 12.3 DNA, RNA, and Protein The Code DNA code is a three-base code. The three-base code in mRNA is called a codon. Chapter 12 Molecular Genetics 12.3 DNA, RNA, and Protein Translation RNA Amino Acid In translation, tRNA molecules act as the interpreters of the mRNA codon sequence. Each anticodon (on tRNA) is complementary to a codon (on mRNA). Codons •64 possible codons •20 different amino acids Codons Start Codon • AUG Stop Codons • UGA • UAA • UAG Molecular Genetics Extra Facts • Genes give instructions for making proteins • It is possible for more than one combo of codons to code for the same amino acid because there are 64 different types of codons, but only 20 amino acids • Takes 3 bases to code for 1 amino acid Chapter 12 Molecular Genetics 12.3 DNA, RNA, and Protein RNA Processing The code on the DNA is interrupted periodically by sequences that are not in the final mRNA. Intervening sequences are called introns. are cut out by enzymes The portions of DNA molecules that actually code for the production of proteins are called exons. parts of the mRNA that are kept and expressed Chapter 12 Molecular Genetics 12.4 Gene Regulation and Mutation Mutations A permanent change that occurs in a cell’s DNA 2 Main Types of Mutations: Gene Chromosomal Chapter 12 Molecular Genetics 12.4 Gene Regulation and Mutation Causes of Mutation Can occur spontaneously Radiation such as UV rays, X rays and gamma rays Chemicals – Mutagens & carcinogens Nondisjunction Viral Infection- HPV Chapter 12 Molecular Genetics 12.4 Gene Regulation and Mutation Body-cell v. Sex-cell Mutation Somatic cell mutations are not passed on to the next generation. Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring. Gene mutations • Point mutations – mistakes with 1 nucleotide – Substitution of the wrong nucleotide (nitrogen base) in place of correct one • Frameshift mutations – occur when a nucleotide is either inserted or deleted, altering the codon sequence – More severe than point mutations because it affects all of the amino acids in the protein Chromosomal mutations • Change in the number or structure of the chromosomes – Duplication – Inversion – Translocation Chapter 12 Molecular Genetics 12.4 Gene Regulation and Mutation