Dna, rna, protein


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Dna, rna, protein

  1. 1. sdn
  2. 2. Frederick Griffith • British bacteriologist • 1928 = designed and performed experiment on rats and bacteria that causes pneumonia. • 2 strains of the bacteria • Type S = causes severe pneumonia • Type R = relatively harmless
  3. 3. Griffith’s Rats 1. First he injected living Type S bacteria into rats:
  4. 4. • Second he injected dead Type S into the rats.
  5. 5. • Next he injected living type R bacteria
  6. 6. • Finally he injected a mixture of living Type R and dead Type S :
  7. 7. Results of experiments: • Because the dead rat tissue showed living Type S bacteria, something “brought the Type S back to life” • Actually one bacterial type incorporated the DNA, or instructions, from the dead bacteria into its own DNA • Known as transformation. Confirmed by Avery, MacLeod, and McCarty in 1944
  8. 8. Oswald Avery • Canadian biologist (18771955) • Discovered DNA in 1944 with a team of scientists.
  9. 9. Hershey and Chase • 1952 • Attempted to solve the debate on whether DNA or proteins are responsible for providing the genetic material.
  10. 10. • They used a bacteriophage (a virus which attacks bacteria) to prove that DNA was definitely the genetic material.
  11. 11. Phoebus A. Levene • Russian born; immigrated to America, moves to Europe. • 1920’s discovered nucleotides (building blocks of DNA) 1. Sugar 2. Phosphate group 3. Nitrogenous base
  12. 12. Composition of DNA
  13. 13. Components and structure of DNA • A very long molecule. 4 nitrogenous bases:
  14. 14. Chargaff’s rules • The relative amounts of adenine and thymine are the same in DNA • The relative amounts of cytosine and guanine are the same. • Named after Erwin Chargaff
  15. 15. Rosalind Franklin • Used X-Ray diffraction to get information about the structure of DNA:
  16. 16. Structure of DNA • Discovered in 1953 by two scientists: • James Watson (USA) • Francis Crick (GBR) • Known as the double-helix model.
  17. 17. The double-helix • A twisted ladder with two long chains of alternating phosphates and sugars. The nitrogenous bases act as the “rungs” joining the two strands.
  18. 18. How long is the DNA molecule?
  19. 19. Chromosomes & DNA replication • The nucleus of one human cell contains approximately 1 meter of DNA. • Histones = DNA tightly wrapped around a protein • Nucleosome:
  20. 20. Chromosome structure:
  21. 21. DNA replication • Must occur before a cell divides. • Each new cell needs a copy of the information in order to grow.
  22. 22. DNA replication. Why needed? • Before DNA strand can be replicated or copied it must be “unzipped” • DNA polymerase (enzyme that unzips) • Starts at many different points. Why?
  23. 23. Completing the replication • After the DNA molecule comes apart, bases of free nucleotides in the nucleus join their complimentary bases.
  24. 24. RNA • Very similar to DNA. • Exceptions: 1) Ribose is the 5-carbon sugar 2) Uracil replaces thymine 3) Single-stranded
  25. 25. mRNA (messenger) • Copies genetic code of DNA by matching bases. • Occurs in the nucleus. • DNA changing to RNA
  26. 26. TRANSCRIPTION • DNA is copied into mRNA with the aid of RNA polymerase. • The RNA polymerase will bind to promoters that act as signals in the DNA sequence to make RNA.
  27. 27. Transcription continued:
  28. 28. Exons and Introns • EXONS • A segment of DNA in eukaryotic organisms that codes for a specific amino acid • INTRONS • A segment of DNA that does NOT code for an amino acid.
  29. 29. Confusing genetic terms: • Polypeptide = a chain of amino acids. • Protein = a complex structure composed of polypeptides • Amino acids = smallest structural unit of a polypeptide. • Gene = a distinct unit of material found on a chromosome
  30. 30. Reading the genetic code • The genetic code is responsible for building all the proteins in the body using 20 different amino acids. • How many 3 letter words can you make from the letters A,T,G and C? • Answer: 64
  31. 31. Codons • A three letter “word” that specifies an amino acid.
  32. 32. Genetic code:
  33. 33. tRNA (transfer) • approx. 80 nucleotides in length. • Cross-like shape • At one end an amino acid is attached • At the other end there is an anticodon • Acts like a truck
  34. 34. Polypeptide assembly • Translation = reading or “translating” the RNA code to form a chain of amino acids. • Known as protein synthesis • Occurs in the cytoplasm. (p.304)
  35. 35. Mutations • The source of variation in a genetic sequence. • Can be either gene or chromosomal mutations. • Point mutations = a change in a single nucleotide in a sequence of DNA.
  36. 36. Frameshift Mutation • Inserting an extra nucleotide which, in turn, shifts the entire sequence one way or the other.
  37. 37. Chromosomal mutations • Involves a change in the number or structure of the chromosomes. • Deletion : when a piece of a chromosome breaks off and is lost. • Duplication : when a segment of a chromosome is repeated • Inversion : when a segment of a chromosome is reversed.
  38. 38. More chromosomal mutations • Translocation : when part of a chromosome breaks off and is attached to a non-homologous chromosome.
  39. 39. Control of gene expression • Genes are often like light switches that can be turned off and on. • Operon = occur in prokaryotes. (bacteria) different genes that work together to activate gene functions
  40. 40. Eukaryotic gene expression • Controlled by complex sequences of DNA. • Example: “TATA box”
  41. 41. Protein Structure • Serve various function including structural roles, catalysts, transporter and hormones • Polymers of amino acids covalently linked through peptide bonds into a chain • Each of amino acid has a fundamental design composed of a central carbon bonded to ; i. a hydrogen ii. a carboxyl group iii. An amino group iv. A unique side chain of R-group
  42. 42. • the characteristic that distinguishes one amino acid from another is its unique side chain, and it is the side chain that dictates an amino acids chemical properties • The unique side chains confer unique chemical properties on amino acids, and dictate how each amino acid interacts with the others in a protein.
  43. 43. Peptide bonds are formed between the carboxyl group of one amino acid and the amino acid of the next amino acid  Peptide bond formation occurs in a condensation reaction involving loss of a molecule of water  The head-to-tail arrangment of amino acids in a protein means that there is a amino group on one end (called the aminoterminus or N-terminus) and a carboxyl group on the other end (carboxyl-terminus or C-terminus).  The carboxy-terminal amino acid corresponds to the last one added to the chain during translation of the messenger RNA.
  44. 44. Levels of Protein Structure • Structural features of proteins are usually described at four levels of complexity a. Primary structure b. Secondary Structure c. Tertiary Structure d. Quaternary Structure
  45. 45. Primary Structure • - the linear arrangement of amino acids in a protein and the location of covalent linkages such as disulfide bonds between amino acids
  46. 46. Secondary Structure • areas of folding or coiling within a protein; examples include alpha helices and pleated sheets, which are stabilized by hydrogen bonding
  47. 47. Tertiary Structure • the final three-dimensional structure of a protein, which results from a large number of non-covalent interactions between amino acids.
  48. 48. Quaternary Structure • Two or more tertiary proteins joined • non-covalent interactions that bind multiple polypeptides into a single, larger protein. Hemoglobin has quaternary structure due to association of two alpha globin and two beta globin polyproteins.