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DNA and RNA Replication, Transcription, and Translation 1 Genetic Controversy Two schools of thought a. Some said protein was material b. Some said DNA was material How was the controversy settled? - The scientific experiments of Griffith, Avery, Hershey and Chase 2 Griffith and Transformation - 1928 - England - Trying to develop a vaccine against pneumonia causing bacteria - Two strains - S(smooth) and R(rough) 3 Heat-killed, disease-causing bacteria (smooth colonies) Disease-causing bacteria (smooth colonies) Dies of pneumonia Harmless bacteria (rough colonies) Lives Heat-killed, diseasecausing bacteria (smooth colonies) Lives Control (no growth) Live, disease-causing bacteria (smooth colonies) Harmless bacteria (rough colonies) Dies of pneumonia 4 RESULTS - Showed that heat killed S strain and live R strain would kill mice - Something was “transforming” the R strain to an S strain - Called it transformation - What was the material? 5 Oswald Avery - 1944 - Wanted to identify Griffith’s transforming material - Used two enzymes a. protein killing b. DNA killing - Showed that no transforming took place when DNA 6 D. Hershey and Chase - 1952 - Working with a bacteriophage - Virus that infects bacteria - Made of only two things a. protein coat b. DNA (genetic) core 7 8 Hershey and Chase Bacteriophage with phosphorus-32 in DNA Bacteriophage with sulfur-35 in protein coat Phage infects bacterium Radioactivity inside bacterium Phage infects bacterium No radioactivity inside bacterium 9 Recap: Was DNA or protein injected? - DNA has phosphorus - Protein has sulfur - Used radioactive phosphorus 32P and radioactive sulfur 35S - Let virus infect bacteria - New viruses full of 32P DNA was being injected! 10 11 The Components and Structure of DNA 1. Called deoxyribonucleic acid 2. Long and thread-like (twisted) 3. Many subunits linked together 4. Subunits called nucleotides 5. 1000’s in a chain-like structure 12 The structure of a nucleotide 1. Phosphate group - same in all 2. Five carbon sugar a. deoxyribose sugar 3. Nitrogenous base - 4 different ones that name the nucleotide 13 Nitrogenous Bases 1. Are different in each nucleotide 2. Names of the four bases a. adenine (A) b. guanine (G) c. thymine (T) d. cytosine (C) Two classes of bases A. purines 1) large double ring 2) A & G B. pyrimidines 1) small single ring 2) T & C 14 Purine and Pyrimidine Structure 15 H. Chargaff - 1949 - Studying the amounts of bases in DNA of living things - His results showed that: a. A always = T b. C always = G - Called Chargaff’s rule - Also called the base pair rule 16 The molecule is completed… - Franklin and her X-ray diffraction picture showed a helix - Watson and Crick adds that it is a double helix with bases in the middle - Called it a “spiral staircase” - Strands are complements of each other - Think of a step ladder a. “sides” are alternating sugar and phosphate groups b. “rungs” are base pairs 1) A = T 2) C = G 17 Nucleotide Hydrogen bonds Sugar-phosphate backbone Adenine Thymine Cytosine Guanine 18 Chromosomes and DNA Replication A. DNA Can Make Copies of Itself 1. Process called replication 2. Done during S phase 3. Needed for new cells 4. DNA unwound using helicases 5. Hydrogen bonds broken between bases 6. DNA polymerase puts new nucleotides in place (A to T and C with G) 7. New copy just like original 19 From Genes To Proteins DNA RNA Double-stranded Single-stranded Deoxyribose Ribose Thymine Uracil 20 RNA (ribonucleic acid) 3 forms of RNA mRNA (messenger) tRNA (transfer) rRNA (ribosomal) RNA is used to take the information in DNA and make proteins (gene expression) 2 stages of gene expression Transcription Translation 21 The Big Idea… During gene expression, the info in DNA is first transcribed as mRNA and then translated via tRNA and used to build a protein. 22 From Genes To Proteins… 1. Transcription: making mRNA from DNA to carry information to the ribosomes. 23 - ALL organisms have a genetic code made of three nucleotide sequences called codons. QuickTime™ and a decompressor are needed to see this picture. - Codons correspond to particular AA and stop signals. 24 The Genetic Code QuickTime™ and a decompressor are needed to see this picture. The Genetic Code QuickTime™ and a decompressor are needed to see this picture. 26 From Genes To Proteins… 2. Translation: Using tRNA to build proteins from the information in mRNA. - Each tRNA molecule carries an amino acid to the ribosomes, by matching its anticodon to a specific codon from the mRNA http://www.youtube.com/watch?v=NJxobgkP EAo GENETIC MUTATIONS Mutations (gene or chromosomal) Changes in DNA Effect depends on where mutation occurs (body or sex cell) & what type of mutation Can be helpful, harmful, or neutral 28 Different Types of Gene Mutations Substitutions = UGU to UGC Effect depends on translation Insertions = nucleotides added Deletions = nucleotides deleted Transposons= DNA segments move spontaneously from one location to another in the same DNA molecule 29 Ex. THE CAT ATE THE RAT (meaningful) Deletion of C = THE ATA TET HER AT (meaningless) 30 Types of Chromosomal Mutations Deletions (whole or part deleted) Duplications (extra copies of parts) Inversions (reverses parts of chromosomes) Translocations (parts break off and relocate) 31 Causes of Mutations? Spontaneous Mutagens (come from environment) UV light Chemicals Carcinogens (cancer causing) 32