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History of DNA

History of DNA. H Biology Winter 2018. What does DNA stand for?. D eoxyribo n ucleic a cid. What is DNA made of?. Which one?. DNA is a macromolecule Made up of nucleotides Covalently bonded together Double stranded Helix “ Spiral ”. What is a nucleotide?. Molecule made of

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History of DNA

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  1. History of DNA H Biology Winter 2018

  2. What does DNA stand for? • Deoxyribonucleic acid

  3. What is DNA made of? Which one? • DNA is a macromolecule • Made up of nucleotides • Covalently bonded together • Double stranded • Helix • “Spiral”

  4. What is a nucleotide? • Molecule made of • Deoxyribose sugar • A phosphate group • A nitrogenous base

  5. How was DNA identified as genetic material? • 1928 – Griffith notices that bacteria can transfer some type of material to other types of bacteria • “Transforming principle”

  6. How was DNA identified as genetic material? • 1944 – Oswald Avery discovered that the transforming principle was DNA (genetic material) • 1952 – Hershey and Chase studied a virus that affects bacteria (bacteriophage) and confirmed that DNA was genetic material

  7. How was the structure of DNA discovered? • 1950 – Erwin Chargaff • Noticed that the same 4 bases are found in the DNA of all organisms • Also noticed that: # of Adenine = # of Thymine # of Cytosine = # of Guanine • “Chargaff’s Rule”

  8. How was the structure of DNA discovered? • 1950s – James Watson and Francis Crick • Worked to figure out DNA’s structure • Thought that DNA might be a helix, but had no evidence • Idea that DNA was a helix came from Linus Pauling

  9. How was the structure of DNA discovered? • 1951-1952 – Rosalind Franklin • Used x-ray diffractions to show DNA was truly a double helix • Worked with Maurice Wilkins

  10. How was the structure of DNA discovered? • 1953 – Watson and Crick • Wilkins (a colleague of Franklin) shows Watson and Crick the x-ray pictures • This information gave Watson & Crick the evidence needed to conclude DNA has a helical shape • Made a model of DNA which was made up of two chains of nucleotides

  11. DNA Structure

  12. DNA - Basics • Deoxyribonucleic Acid • Stores and transmits genetic info • Tells the cells which proteins to make and when to make them

  13. DNA - Basics • Made up of nucleotides: • Phosphate group • Sugar • Nitrogen bases (4 total) • Adenine (A) • Thymine (T) • Cytosine (C) • Guanine (G) • Double helix structure (twisted ladder)

  14. All about that base, ‘bout the base…

  15. Nitrogen Bases • 2 groups that bases are put in based on structure • Purines→ 2 carbon rings • Adenine (A) • Guanine (G) • Pyrimidines→ 1 carbon ring • Cytosine (C) • Thymine (T) Pure As Gold Cing Tut lived in a Pyramid

  16. Base Pairing Rules • Adenine (A) always matches w/ Thymine (T) • Cytosine (C) always matches w/ Guanine (G)

  17. Base Pairing Rules • Why these base pairings? • Bases are specific! • Sizes of the bases (rings) • Number of H bonds formed with each other • The sizes of the bases (and how they pair) also determine the structure of the larger DNA molecule

  18. Size of Bases Purine + Purine = Too wide Pyrimidine + Pyrimidine = Too Narrow

  19. NO NO Purine + Pyrimidine = Perfect Fit YES!

  20. What makes up the “backbone” of DNA? • The sides of the ladder are made up of: • 1) Sugar • 2) Phosphate • Alternate along backbone

  21. What Holds Everything Together!? • Weak Hydrogenbonds connect the nitrogenous bases to each other • Covalent bonds connect the sugars and phosphates to each other!

  22. DNA Structure Summary • Double Helix (twisted ladder) • Sides of ladder = sugar/ phosphate backbone • Rungs of the ladder = nitrogen bases

  23. DNA Replication

  24. Protein Synthesis • 3 major processes: • Replication→ DNA doubles to form 2 new DNA molecules • Transcription→ DNA info copied to RNA • Translation→ building a protein according to RNA instructions • Uses mRNA, rRNA, and tRNA

  25. DNA Replication • Occurs in nucleus • DNA is copied • Process: • Enzyme helicase“unzips” strands of DNA by breaking H bonds at several places along segment of DNA  called “origins of replication”

  26. Point at which the strands separate is called the replication fork

  27. primase

  28. DNA Replication • DNA Polymerase adds nucleotides to create two NEW identical daughter strands, by adding nucleotides (A to T and G to C) • Also fills-in gaps between Okazaki fragments

  29. DNA Replication • Okazaki fragments are large chunks of nucleotides • DNA Ligase joins Okazaki fragments and seals nicks in the backbone

  30. Semi-Conservative • DNA replication is said to be semi-conservative • Each new double-helix created contains one strand from the helix from which it was copied

  31. Direction of Replication Enzyme DNA Polymerase helps build the new strands from the 5’ 3’ direction

  32. Why Replication? DNA replication is necessary to create identical copies of DNA, so it can be passed onto a new cell (cell division & reproduction) Okazaki fragments are newly made DNA fragments that form on the lagging template

  33. Accuracy of Replication • Very low mistake rate (1/billion!) because cells have enzymes (like DNA Polymerase) that proofread, recognize, and fix mistakes! • HOWEVER, mistakes can happen  MUTATIONS(cancer)

  34. Review: DNA Replication A new sugar-phosphate backbone is made for each new strand Base pairs are added (A-T and C-G) Two strands are created in place of the original strand

  35. Protein Synthesis Pt. 1 - Transcription

  36. What is Transcription? • DNA information is copied into an RNAmessage • Occurs in the nucleus • Base pair change: in RNA Thymine (T) is replaced with Uracil (U)

  37. Transcription • During transcription, the Thymine (T) base pair of DNA changes to Uracil (U)in RNA • Uracil is a pyrimidine • Uracil requires less energy to create vs. Thymine • Uracil also prevents Nuclease from breaking down DNA during Protein Synthesis

  38. Why RNA? • RNA – Ribonucleic Acid • How does DNA get out of the nucleus and go to the ribosomes where the proteins are made? • It CAN’T! DNA cannot leave the nucleus! • So, it copies itself into RNA and that leaves and goes to the ribosomes • EXAMPLE – library book, photocopy Library book = DNA Photocopy = RNA

  39. DNA vs. RNA NameDeoxyribonucleic Acid Ribonucleic Acid Sugar Deoxyribose Ribose • Nitrogen Bases A, C, G & A, C, G & • Thymine (T) Uracil (U) • Location Inside nucleus onlyIn and out of nucleus StrandedDouble stranded Single Stranded

  40. Steps of Transcription • RNA polymerase “opens” a section of DNA (so the double helix strands are separate)

  41. Steps of Transcription • Using onestrand of DNA as a template, RNA polymerase builds a complementary strand of RNA nucleotides • This RNA strand is called mRNA

  42. Steps of Transcription • Base pairing rules are the same as with DNA, except Uracil (not Thymine) pairs with Adenine • DNA: A C T G • RNA: U G A C • Once the entire gene (segment of DNA) has been transcribed, RNA polymerase releasesnew strand • Strand exits the nucleus through the pores in the nuclear envelope  goes to cytoplasm  ribosomes (protein factories!

  43. Practice Transcribing TCT • DNA Complementary – A T C _____ _____ • DNA Template - _____ A G A _____ • mRNA - _____ _____ U A G **NOTE: Always create the mRNA strand using the DNA Template** TAG TAG ATC AUC UCU

  44. Protein Synthesis Pt. 2 - Translation

  45. Codons • For every 3 bases copied from DNA to RNA, we have a codon • Codons are important, because they “code” for specific amino acids • These amino acids then build a larger protein molecule!

  46. Practice Finding the Correct Amino Acid CCAAGAGUGUGAAUG CAG Remember, ALWAYS use mRNA codons to find the correct amino acids!

  47. Protein Synthesis Canada – French – Bonjour! – DNA – TACGCT USA – English –Hello! –mRNA –AUGCGA Mexico – Spanish – Hola! –Protein – MET-ARG • Protein synthesis consists of 2 mains parts: • Transcription– DNA is copied in the nucleus, the result is the formation of mRNA • Translation– mRNA travels to the cytoplasm and attaches to a ribosome; with the help of tRNA a protein is made • Cells translate an RNA message (English) into amino acids (Spanish)

  48. Three types of RNA • Transcription makes 3 types of RNA: • rRNA – ribosomal RNA - Makes up part of the ribosomes (protein factories) • tRNA – transfer RNA - Brings the amino acids from the cytoplasm to the ribosomes to make the growing protein 3. mRNA – messenger RNA - A message (genetic code) that goes to the ribosomes and is translated to form a protein

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