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Understanding dna

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  • 1. Understanding DNA Presented by: Mrs. Nelson
  • 2. OVERVIEW  Name the four organic compounds found in all living things.  The focus of this chapter will be:  What are the elements found in nucleic acids?  What is the subunit?  What are the two types of nucleic acids?  What is the function of DNA?
  • 3. Discovering DNA  Frederick Griffith studied bacteria cause pneumonia.  Smooth strain -disease  Rough strain - harmless  What caused the difference?
  • 4. Griffith’s Experiment
  • 5. Griffith’s Conclusion  The harmless bacteria could “acquire” the ability to cause disease. How?  Transformation  Bacteria can take “something” from each other  By doing so, they can take on different traits.
  • 6. Transformation
  • 7. Discovery of DNA  Griffith didn’t know what it was that bacteria were taking from each other.  He did know that this “something” gave organisms their traits.  Later, it was discovered that this was DNA.
  • 8.  DNA (Deoxyribonucleic acid).  All living things contain DNA.  Source of genetic traits because it is the the directions cells use to build proteins.
  • 9. Where is DNA? Cell Nucleus Chromosome Gene DNA
  • 10. Chromosomes a closer look …
  • 11. What does DNA look like?  DNA made subunits: nucleotides  Nucleotide: sugar (deoxyribose), phosphate group, nitrogen base  DNA 4 nitrogen bases: adenine, guanine, thymine and cytosine  ***Scientists knew DNA was made of these parts- they did NOT know how all the pieces fit together!
  • 12. “The race to build the 1st DNA model”  Rosalind Franklin 1) 2 strands like a twisted rope 2) Molecules were evenly spaced out…
  • 13. 2 Categories of Bases:  Purines- “larger bases” adenine (A) guanine (G)  Pyrimidines- “smaller bases” cytosine (C) thymine (T)
  • 14. Chargaff’s Rule  Measured amounts of each base in various organisms and found: amount of adenine (A) = thymine (T) amount of cytosine (C) = guanine (G)  This meant A only bonds T and C only bonds G
  • 15. Structure of DNA  Double helix- “spiral staircase”, 2 strands of nucleotides  “siderails” sugar and phosphate  “rungs” bases (base pairs connected by hydrogen bonds)  bases attach sugar molecules, phosphate molecules between sugars  complementary- sequence of bases on one strand determines the sequence of bases on other strand  antiparrallel- strands are oriented opposite to each other with respect to the carbon atoms in the sugar molecules
  • 16. Watson and Crick “Double Helix”
  • 17. Antiparallel- 5’ and 3’ ends
  • 18. What is the job of all cells???  Process called Protein Synthesis:  DNARNA Protein  2 stages: Transcription and Translation
  • 19. RNA (Ribonucleic acid)  Nucleic acid… helps DNA make proteins  _____RNA____vs._____DNA___ single strand double strand sugar= ribose sugar= deoxyribose A, C, G, U (uracil) A, T, C, G mRNA, rRNA, tRNA “DNA is DNA” all over nucleus only
  • 20. Structure RNA
  • 21. Transcription: Part 1 : Protein Synthesis  Problem: DNA (directions build protein) can not leave nucleus go to ribsome  Information DNA copied RNA (messenger)  DNA complementary mRNA  occurs nucleus
  • 22. Steps in Transcription  1st - DNA untwists  2nd- enzyme RNA polymerase moves along DNA strand creating “complementary mRNA”
  • 23. Genetic Code  Goal make protein  protein - bunch amino acids  every 3 bases (nucleotides) mRNA code amino acid - called codon  DNA: ATA CGG AAT (3 triplets)  mRNA: UAU GCC UUA (3 codons)
  • 24. What amino acids are needed to build the protein? mRNA - UAU GCC UUA
  • 25. Translation: Part 2: Protein Synthesis Protein built Happens ribosome requires tRNA (transfer RNA) tRNA carries amino acids ribosome mRNA complementary tRNA
  • 26. tRNA  One end amino acid  Other end 3 bases called anticodon  anticodon complementary codon (mRNA/tRNA) “safety check”
  • 27. Steps Translation  mRNA leaves nucleus goes ribosome (made of rRNA)  1st- “start” codon  2nd- tRNA brings amino acids ribosome (codons-anticodons pair)  3rd- bonds join amino acids  4th- stop codon  ribosome releases protein cytoplasm
  • 28. What is DNA Replication?  Process of “copying” DNA exactly  Process must be completed before cells can divide (reproduce)  Multicellular organisms- cell division = growth and repair/replacement  Unicellular organisms- cell division = reproduction
  • 29. DNA Replication
  • 30. DNA Replication (process)  1st - enzyme helicase attaches to DNA and causes it to unzip at the replication fork (must break hydrogen bonds-bases)  2nd - enzyme DNA polymerase moves along leading strand adding complementary bases (continuously in 5’3’ direction toward replication fork)  3rd - lagging strand completed next but Okazaki fragments result (discontinuous away from replication fork)  4th - enzyme ligase joins the fragments on lagging strand  Summary: 1 DNA molecule 2 DNA molecules
  • 31. Mutations  If DNA does not get copied correctly, a mutation can arise.  Mutation- change in DNA sequence  “Mutagens” are things found in the environment that can get into your cells and “scramble” your DNA.  Three known mutagens: 1.) chemicals 2.) viruses 3.) UV radiation
  • 32. Mutations – change in DNA  Substitution
  • 33. Effects of Mutations…  DNA carries instructions to build proteins.  If the DNA is changed, proteins will be built incorrectly.  Two general types of mutations: 1. Gene mutation (effects one gene on chromosome) 2. Chromosome mutation  Three different types of gene mutations 1. subsitution 2. Insertion 3. Deletion
  • 34. Substitution THE FAT CAT SAT THE FAT RAT SAT Changing one letter, changes one word, which changes the meaning of the sentence.
  • 35. Substitution DNA: TAC GCA TGG AAT MRNA: AUG CGU ACC UUA A.ACID: Met - Arg - Thr - Leu DNA: TAC GTA TGG AAT MRNA: AUG CAU ACC UUA A. ACID: Met - His - Thr - Leu Results in one amino acid being altered
  • 36. Insertion THE FAT CAT SAT THE SFA TCA TSA T Inserting one letter, shifts all other letters over, creating several words to be incorrect. This is also known as a “frame-shift” mutation.
  • 37. Insertions DNA: TAC GCA TGG AAT MRNA: AUG CGU ACC UUA A.ACID: Met - Arg - Thr - Leu DNA: TAT CGC ATG GAA T MRNA: AUA GCG UAC CUU A A.ACID: Iso - Ala - Tyr - Leu Results in several amino acids being altered
  • 38. Deletion THE FAT CAT SAT THE ATC ATS AT Similar to Insertion (frame-shift). REMOVE
  • 39. Deletion DNA: TAC GCA TGG AAT MRNA: AUC CGU ACC UUA A.ACID: Met - Arg - Thr - Leu DNA: TAG CAT GGA AT MRNA: AUC GUA CCU UA A. ACID: Iso - Val - Pro - None Results in several amino acids being altered
  • 40. Significance of Mutations  Some mutations may be “neutral,” they won’t have an effect on the protein being built.  Some mutations can be very harmful and cause genetic disorders.  Some mutations lead to genetic variation in a species. (Ex. Tongue rolling)