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Molecular Biology of the Gene: DNA Replication, Transcription, and Translation

This chapter explores the processes of DNA replication, transcription, and translation, and their role in transferring genetic information from DNA to RNA to protein. It also discusses the molecular structure of DNA and the genetic code.

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Molecular Biology of the Gene: DNA Replication, Transcription, and Translation

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  1. Chapter 10 Molecular Biology of the Gene

  2. http://www.pbs.org/wgbh/nova/body/cellular-factory.html • Video #96 (Genes, DNA, Chrom)

  3. Information transfer is from DNA  RNA  protein • Replication • What is it? • Where does it occur? Copying DNA for division In the nucleus REPLICATION

  4. Information transfer is from DNA  RNA  protein • Transcription • What is it? • Where does it occur? Making mRNA from DNA In the nucleus

  5. Information transfer is from DNA  RNA  protein • Translation • What is it? • Where does it occur? Converting mRNA into a protein In the cytoplasm, at a ribosome

  6. 2. DNA as source of genetic information a. Hershey-Chase experiment showed DNA rather than protein to be the genetic material passed on from one generation to the next

  7. DNA

  8. DNA

  9. DNA

  10. DNA

  11. DNA

  12. DNA

  13. 2. DNA as source of genetic information b. additional evidence – cell doubles DNA prior to mitosis, and then splits the DNA evenly among daughter cells

  14. Watson and Crick

  15. 3. Molecular structure of DNA • a. Watson and Crick described the three dimensional structure of DNA one year after Hershey and Chase identified DNA as the genetic material

  16. 3. Molecular structure of DNA • b. DNA, along with RNA, are nucleic acids which are composed of nucleotides • c. Nucleotides consist of a sugar (ribose or deoxyribose), a nitrogenous base (A, G, C, T, or U), and a phosphate group

  17. 3. Molecular structure of DNA • d. Structure of single DNA strand • 1. sugar-phosphate backbone • 2. bases covalently attached to sugar and ‘hang off’ the side

  18. 3. Molecular structure of DNA • e. double helical structure • 1. double stranded • 2. arranged in helix

  19. 3. Molecular structure of DNA • 3. hydrogen bonds between nitrogenous bases hold strands together (remember, hydrogen bonds are weak chemical bonds)

  20. 3. Molecular structure of DNA 4. the two strands of DNA run “anti-parallel”; i.e., one strand runs in 5’-3’ direction while the other runs in the 3’-5’ direction The primed numbers refer to the C of the sugar. The bases are attached to the 1’ carbon and the phosphate groups are attached at the 5’ sugars. Nucleotides form covalent bonds between the 3’ carbon of one and the 5’ carbon of the other nucleotide.

  21. VIDEO #47 (DNA structure and Replication CC)

  22. 4. DNA replication • a. complementary base pairing governs how new DNA molecules are synthesized using existing DNA as templates (fig 10.4) • 1. A with T • 2. G with C

  23. 4. DNA replication • b. DNA synthesis is semiconservative; i.e., the two strands are separated and each strand is used as a separate template.

  24. 4. DNA replication • c. DNA synthesis occurs along each of the separated strands thus resulting in two new double-stranded molecules of DNA

  25. 4. DNA replication • d. New nucleotides are added to a growing strand of DNA one at a time, and this energy-requiring reaction is catalyzed by an enzyme, DNA polymerase

  26. 4. DNA replication • e. The new strands are synthesized 5’-3’ and anti-parallel with the template strands (10.5)

  27. 4. DNA replication • f. The two new strands of DNA are synthesized as the leading and lagging strand

  28. CTATGTCGACATGCAGC CTATGTCGACATGCAGC GATACAGCTGTACGTCG GATACAGCTGTACGTCG 4. DNA replication • g. process of replication • 1. the enzyme helicase unwinds the double stranded DNA, while single stranded binding proteins stabilize the templates

  29. 4. DNA replication • 2. primase adds RNA primers to the exposed templates because DNA polymerase must add new nucleotides to a 3’ end of an existing nucleotide in an already started strand

  30. CTATGTCGACATGCAGC GATACAGCTGTACGTCG 5’3’ GATACAGCTGTACGTCG CTATGTCGACATGCAGC 3’ 5’

  31. 4. DNA replication • 3. DNA polymerase adds one nucleotide at a time in the 5’ – 3’ direction along the leading strand and lagging strand (leading strand is synthesized continuously while the lagging strand is synthesized in Okazaki fragments)

  32. 4. DNA replication • 4. Another DNA polymerase replaces the RNA primer • 5. Ligase seals the Okazaki fragments

  33. Video #48 (DNA, Hot Pockets)

  34. 1. Overview of protein synthesis Process = DNA to RNA to protein

  35. 1. Overview of protein synthesis Specific sequences of DNA in genes code for specific sequences of RNA which in turn code for specific sequences of amino acids in proteins

  36. 1. Overview of protein synthesis • compartmentalization • transcription in nucleus • translation (protein synthesis) in cytoplasm

  37. 2. Genetic Code • mRNA is read 3 nucleotides at a time; i.e., one amino acid coded for by three nucleotides

  38. 2. Genetic Code b. each set of three nucleotides is referred to as a codon c. use genetic code of RNA codons to predict amino acid sequence in synthesized peptide

  39. 2. Genetic Code c. use genetic code of RNA codons to predict amino acid sequence in synthesized peptide

  40. Using the Chart • CAU • The codon CAU codes for His

  41. 3. Transcription • Initiation- RNA polymerase binds to promoter sequence of DNA, unwinds DNA and starts transcription at start site

  42. 3. Transcription b. Elongation– RNA polymerase makes new strand of RNA in 5’ to 3’ direction; i.e., it adds new nucleotides to the 3’ end of the growing RNA strand, DNA reforms double strand behind polymerase ATG CAT GTC GAT CAC TAA AGT TTA AUG CAU GUC GAU CAC UAA AGU UUA ATG CAT GTC GAT CAC TAA AGT TTA TAC GTA CAG CTA GTG ATT TCA AAT

  43. 3. Transcription c. Termination– RNA polymerase reaches a terminator sequence of DNA and polymerase along with the newly synthesized mRNA are released

  44. 3. Transcription d. Eukaryotic RNA is processed in the nucleus before final mRNA is sent to cytoplasm

  45. 3. Transcription e. One gene (DNA) is read at a time by RNA polymerase in eukaryotes (monocystronic)

  46. 3. Transcription f. Multiple genes can be read at a time by RNA polymerase in prokaryotes (polycystronic)

  47. 4. Translation • synthesis of proteins using RNA as a template • catalyzed by ribosomes in the cytoplasm

  48. What Translation Looks Like

  49. 4. Translation c. involves a variety of other players 1. t RNA transfer 2. m RNA messenger 3. r RNA ribosomal

  50. 5. tRNA • interpreters between nucleic acid language and protein language; i.e., translation • single stranded nucleic acid made via transcription just like mRNA

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