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HISTORY: 1928 : Frederick Griffith

HISTORY: 1928 : Frederick Griffith. Performed bacterial transformation experiments with Streptococcus pneumoniae. NO pneumonia. Causes pneumonia. Causes Pneumonia!. NO pneumonia. Transformation :. Cell takes in and integrates external DNA. By 1940, Known information included:.

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HISTORY: 1928 : Frederick Griffith

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  1. HISTORY: 1928: Frederick Griffith Performed bacterial transformation experiments with Streptococcuspneumoniae. NO pneumonia Causes pneumonia Causes Pneumonia! NO pneumonia

  2. Transformation: Cell takes in and integrates external DNA

  3. By 1940, Known information included: heredity material • Chromosomes carry: • Chromosomes are made of: DNA & protein • Scientists assumed: protein was the genetic material

  4. 1944: Avery, McCarty & MacLeod • Proved hereditary agent (in bacteria) was: DNA Enzymes destroy DNA Enzymes destroy lipids, carbs, and proteins Enzymes destroy RNA • HOW? They repeated bacterial transformation experiments with Streptococcuspneumoniae, BUT: Used purified cell components instead of whole cells

  5. Chargaff: Analyzed the DNA composition of different organism: proved A=T and C=G Found DNA to be: species specific & more complex than thought

  6. 1952: Hershey & Chase Conducted experiments with the T2 bacteriophage (virus).

  7. Used radioactive isotopes to tag DNA. Provided powerful evidence that nucleic acids (not proteins): are the hereditary material.

  8. Sparked research by many famous scientists who contributed to the discovery of DNA’s structure and chemical makeup: Pauling, Wilkins, and Rosalind Franklin: x-ray diffraction

  9. 1953: Watson & Crick Published their model of DNA structure in Nature magazine. 3 minute clip with watson. Link on right side of page http://www.pbs.org/wnet/dna/episode1/index.html# with Wilkins (Franklin had died at age 38) Won Nobel prize in 1962:

  10. DNA STRUCTURE: 2 strands: Double helix Remember, Monomer units = nucleotides 3 parts of a nucleotide: Deoxyribose 2.phosphate group 3.nitrogen base Nitrogen bases are either purines (adenine & guanine) or pyrimidines (cytosine & thymine) HYDROGEN bonds hold A-T and C-G Bonding: DNA structure video: (1:19) http://www.youtube.com/watch?v=qy8dk5iS1f0

  11. DNA Replication: during S phase of interphase Fast Complex (See Figure 16.9, p. 299 for the basic concept) Remarkably accurate: errors = 1/billion nucleotides

  12. 1958: Meselson & Stahl Used radioisotope labeling experiments to prove DNA replication is semi-conservative. Semi-conservative: daughter DNA molecules are ½ old & ½ new Semi-conservative model (0:43) http://youtube.com/watch?v=rpwjZX_z5rg&feature=related

  13. DNA replication (1:59) http://www.youtube.com/watch?v=teV62zrm2P0&feature=related DNA Replication STEPS Strand separation: Involves several enzymes: Helicase: unwinds double helix Simple Strand Binding Protein: stabilizes unwound DNA Topisomerase: “unknots” DNA strands as they unzip

  14. Origins of Replication: Sites where DNA replication begins. (See figure 16.12, p. 301) Eukaryotic Chromosomes: Have many origins (faster replication) Replication forks (Y shaped) exist at each end of the replication “bubbles”

  15. Priming: DNA replication begins by adding: RNA primer (primase) removes the RNA and replaces it with DNA DNA polymerase:

  16. Elongating a New DNA Strand: DNA Polymerases: Add complimentary nucleotides in a 5’ to 3’ direction (only adds onto the 3’) Energy needed to add nucleotides is provided by the hydrolysis of nucleoside triphosphates (similar to ATP)

  17. Due to DNA’s antiparallel strands, replication is continuous on 1 strand and fragmented on the other. Called: leading and lagging strands Okazaki Fragments: joined by DNA ligase (lagging strand) Telomeres: repetitive sequence at ends of DNA (NO genes) added by telomerase

  18. Proofreading and DNA repair: Initial pairing errors occur about 1/10,000 Accidental DNA changes can be caused by: chemicals, radiation, x-rays, UV light... Most errors are repaired by: more than 130 kinds of proofreading enzymes (in humans)

  19. HISTORY: 1909: Garrod Suggested genes dictate phenotypes through: enzymes (catalyzing reactions) 1930’s: Beadle & Ephrussi Speculated that Drosophila eye color mutations resulted from: missing enzyme 1942: Beadle & Tatum Used bread mold to demonstrate the relationship between: genes and enzymes Formulated the “one-gene-one-protein” hypothesis: each gene codes for a specific polypeptide (more accurate to say one gene = either polypeptide or RNA product)

  20. Do You REMEMBER This Protein Information?!? structures, enzymes, hormones Main Protein functions: shape Protein function is determined by its: amino acid sequence Protein shape is determined by its: Protein amino acid sequence is determined by its: DNA code

  21. Protein Synthesis = 2 step process: Transcription (inside nucleus): making RNA (from DNA code) making protein (from mRNA code) Translation (outside nucleus):

  22. How RNA differs from DNA: 1 strand (not double) Ribose sugar (instead of deoxyribose) Nitrogen bases: URACIL replaces thymine (A-U and C-G) 3 Main Types of RNA: messenger (mRNA) transfer (tRNA) ribosomal (rRNA) (Eukaryotes also have snRNA & SRP RNA p. 321)

  23. The Genetic Code 4 base “alphabet” must code for: 20 different amino acids sequence of 3 nucleotides on mRNA Code “word” (codon) = redundancy (insurance?) Notice: 1961 (Nirenberg) made artificial mRNA and deciphered the 1st codon: UUU = phenylalanine

  24. DNA Code 64 Different Codons: 61 code for amino acids AUG has dual function: “Start” signal and methionine UAA, UAG, & UGA: “Stop” signal (NOT a.a.)! Reading Frame: codons must be read as triplets Code is universal: same in almost ALL cells (even prokaryotes). Suggests _________________ common ancestry

  25. General TRANSCRIPTION Information: Catalyzed by RNA polymerases. RNA polymerase functions: Separate DNA Strands Link RNA nucleotides Add nucleotides in a 5’ to 3’ direction Prokaryotes have 1 type, Eukaryotes have 3: One for each type of RNA Transcription Unit: nucleotide sequence that can be transcribed into a single RNA strand. Corresponds to one: gene Transcription (2:30) http://www.youtube.com/watch?v=mQClpqDBlSs&feature=related

  26. TRANSCRIPTION occurs in 3 Main Steps: Initiation, Elongation, Termination Initiation: promoter regions RNA polymerases bind to DNA at: Promoter = initiation site and “upstream” recognition site (such as TATA box) Transcription Factor: proteins which help polymerase bind to promoter

  27. Elongation of the RNA strand: Once bound to DNA, RNA polymerase: untwists & opens 10-20 base section of DNA RNA nucleotides are base paired to ONLY ONE strand of the DNA (template) RNA nucleotides are added to 3’ end of: elongating strand Newly formed RNA strand peels away from DNA template: DNA will “zip” shut when done Rate = 30 – 60 nucleotides / second One gene can be transcribed simultaneously by several polymerases in a row. Why? To make a lot of that protein

  28. Termination: Terminator sequence causes release of RNA polymerase: stops transcription Prokaryotes: release RNA transcript directly for use. Eukaryotes: process RNA transcript to form specific type (mRNA) before it leaves nucleus

  29. mRNA processing: Guanosine triphosphate (GTP) cap added to: 5’ end to protect and attach later to ribosome Poly-A tail added to 3’ end (50-250 A’s) same 2 functions, plus aids exit from nucleus Intron (non-coding) regions are removed and exons (components of actual gene): spliced together

  30. Functions of Introns? Possible Regulatory Role: gene activity, possibly helps mRNA exit nucleus Allows one gene to have multiple functions: alternative RNA splicing gives rise to diff. protein Evolutionary Role: Allows for increased chance of crossing over within a gene: produces novel versions of a gene. Increases recombination.

  31. General TRANSLATION Information: ALL 3 types of RNA are involved. Messenger RNA (mRNA): Proteins are synthesized according to the mRNA’s _______________ genetic message Transfer RNA (tRNA): Single strand folded into a “t” shape (2-D) One end is specific for 1 of the 20 amino acids The other end (anticodon): base pairs to an mRNA codon “Wobble”: base pair rules between codon & anticodon are flexible at 3rd base site

  32. Ribosomal RNA (rRNA): Joins with many proteins to form ribosomes. Most abundant type of RNA. Each ribosome = 2 subunits which join: only during protein synthesis Ribosomes have a binding site for mRNA AND 3 binding sites for tRNA (in order) A Site: holds tRNA carrying: the next amino acid to be added to the chain. P Site: holds tRNA carrying: the growing polypeptide strand. E Site: (Exit) is where the discharged tRNA leaves the ribosome

  33. http://www.youtube.com/watch?v=D5vH4Q_tAkY Translation 2:16 TRANSLATION also occurs in 3 Main Steps: Initiation, Elongation, Termination Initiation: Small Ribosomal subunit bonds to BOTH: mRNA and the initiator tRNA (methionine) Large Ribosomal subunit bonds to Small Ribosomal subunit The ____________ is in the ______ and the _________ accepts the next tRNA. initiator tRNA P site A site

  34. What type of bond forms to join the 2 amino acids in the ribosome? Elongation: PEPTIDE tRNA in the A site is translocated (shifted) to the P site along with the mRNA, bringing the next codon into the A site. A new tRNA fills the A site. Another translocation occurs and the first tRNA is released from the: E site and new tRNA fills the. A site Process repeats (over and over).

  35. Termination: mRNA codon signaling “stop” reaches A site: UAA, UAG, UGA (not amino acids) Protein release factor binds to stop codon & causes: release of polypeptide & tRNA in P site Ribosomal subunits: separate

  36. MUTATIONS & their effects on Proteins Mutation = a permanent change in DNA Point mutations = change in 1 nucleotide pair

  37. Two types of Point mutations = Substitutions and Insertions / Deletions Substitutions: May have no effect due to the redundancy of codons & similarities between amino acids. inserts different a.a. Missense mutation = Nonsense mutation = becomes a stop codon: inserts NO a.a.

  38. Insertions / Deletions:addition or loss of nucleotide pairs. Usually more harmful: cause a frameshift of ALL following triplet codons.

  39. Mutagenesis= the creation of mutations Spontaneous: mistakes in DNA replication, repair, or recombination Exposure to mutagens (physical or chemical agents): radiation, drugs... (many are carcinogens)

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