Understanding dna


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Understanding dna

  1. 1. Understanding DNA Presented by: Mrs. Nelson
  2. 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. 3. Discovering DNA  Frederick Griffith studied bacteria cause pneumonia.  Smooth strain -disease  Rough strain - harmless  What caused the difference?
  4. 4. Griffith’s Experiment
  5. 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. 6. Transformation
  7. 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. 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. 9. Where is DNA? Cell Nucleus Chromosome Gene DNA
  10. 10. Chromosomes a closer look …
  11. 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. 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. 13. 2 Categories of Bases:  Purines- “larger bases” adenine (A) guanine (G)  Pyrimidines- “smaller bases” cytosine (C) thymine (T)
  14. 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. 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. 16. Watson and Crick “Double Helix”
  17. 17. Antiparallel- 5’ and 3’ ends
  18. 18. What is the job of all cells???  Process called Protein Synthesis:  DNARNA Protein  2 stages: Transcription and Translation
  19. 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. 20. Structure RNA
  21. 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. 22. Steps in Transcription  1st - DNA untwists  2nd- enzyme RNA polymerase moves along DNA strand creating “complementary mRNA”
  23. 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. 24. What amino acids are needed to build the protein? mRNA - UAU GCC UUA
  25. 25. Translation: Part 2: Protein Synthesis Protein built Happens ribosome requires tRNA (transfer RNA) tRNA carries amino acids ribosome mRNA complementary tRNA
  26. 26. tRNA  One end amino acid  Other end 3 bases called anticodon  anticodon complementary codon (mRNA/tRNA) “safety check”
  27. 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. 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. 29. DNA Replication
  30. 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. 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. 32. Mutations – change in DNA  Substitution
  33. 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. 34. Substitution THE FAT CAT SAT THE FAT RAT SAT Changing one letter, changes one word, which changes the meaning of the sentence.
  35. 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. 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. 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. 38. Deletion THE FAT CAT SAT THE ATC ATS AT Similar to Insertion (frame-shift). REMOVE
  39. 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. 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)