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Chapter 2

Chapter 2. An Introduction to Genes and Genomes. Introduction to Molecular Biology. Prokaryotic Cell Structure. Prokaryotic Cell. Eukaryotic Cell. Eukaryotic Cell Structure. Eukaryotic Cell Structure. Animal Cell. Plant Cell. Let’s in on a cell!. Zoom.

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Chapter 2

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  1. Chapter 2 An Introduction to Genes and Genomes

  2. Introduction to Molecular Biology

  3. Prokaryotic Cell Structure Prokaryotic Cell Eukaryotic Cell

  4. Eukaryotic Cell Structure

  5. Eukaryotic Cell Structure Animal Cell Plant Cell

  6. Let’s in on a cell! Zoom DNA Zoom Interactive

  7. DNA Discovery (visit DNAi.org) • Miescher – identified a nuclear substance he called nuclein • Griffith – performed the first transformation • Avery, McCarty, and Macleod – identified Griffith’s transforming factor as DNA • Chargaff – proved that the percentage of the DNA bases adenine always equaled thymine and guanine always equaled cytosine • Wilkins, Franklin, Watson & Crick – demonstrated the structure of DNA

  8. Structure of DNA • Deoxyribose Sugar • Phosphate • Nitrogen Base

  9. Structure of DNA • Purines – double ring • Pyrimidines – single ring

  10. Structure of DNA Nucleic Acid Overview

  11. Structure of DNA

  12. DNA Replication • When DNA makes an exact copy of itself

  13. DNA Replication

  14. DNA Replication • The first step in DNA replication is for the enzyme, helicase, to unzip the double stranded DNA molucule.

  15. DNA Replication • Proteins hold the two strands apart. • An RNA primer lays down on each strand of DNA.

  16. DNA Replication • DNA polymerase extends the primer by adding complementary nucleotides. • DNA polymerase can only extend in the 5’ → 3’ direction

  17. DNA Replication • Leading strand follows helicase. • Lagging strand must wait for replication fork to open and therefore forms discontinous Okazaki fragments. • Ligase seals the nicks in the DNA backbone between the Okazaki fragments. helicase

  18. Let’s put it all together • Click on the animation below. • Select the button for the “whole picture”. DNA Replication Animation

  19. Transcription • Making an RNA copy from a DNA template RNA polymerase

  20. RNA Structure • Uracil instead of thymine • Ribose sugar instead of deoxyribose sugar • Single stranded • Can leave the nucleus

  21. RNA Structure • mRNA – RNA copy of DNA that carries genetic information from the nucleus to the ribosomes • rRNA – makes up the ribosomes • tRNA – carries amino acids to ribosomes for protein synthesis

  22. Transcription • RNA polymerase binds to a promoter region on double stranded DNA and unzips the double helix.

  23. Transcription • Free RNA nucleotides pair with the complementary DNA of the template strand

  24. Transcription • RNA is processed • Introns are spliced out • 7 methyl guanosine cap • Poly-A tail

  25. Transcription • mRNA leaves the nucleus and travels to the ribosomes in the cytoplasm ribosome nucleus

  26. Let’s put it all together • Transcription Animation

  27. Practice

  28. Central Dogma of Molecular Biology Click to see Video Animation

  29. Translation • Making protein from mRNA

  30. Translation • Important Definitions • A codon is composed of 3 RNA nucleotides • Each codon codes for one amino acid • Protein does the work in a cell

  31. Translation

  32. Translation

  33. Third Base

  34. Translation

  35. Translation

  36. Translation

  37. Translation • Asparagine, Serine, Methionine • Tryptophan, Glycine, Lysine • Proline, Leucine, Serine • Aspartic acid, Histidine, Threonine

  38. Translation • Always begins at a start codon and ends at a stop codon. • The region between the start and stop codons is called the open reading frame (ORF)

  39. Practice • Click on the animation to transcribe and translate a gene. Click to see animation

  40. Translation Initiation • mRNA attaches to the small subunit of a ribosome • tRNA anticodon pairs with mRNA start codon • Large ribosomal subunit binds and translation is initiated amino acid tRNA anticodon

  41. Translation Elongation • Anticodon of tRNA carrying next amino acid binds to codon on mRNA • A peptide bond joins the amino acids and the first tRNA is released.

  42. Translation Termination • Amino acid chain continues until a stop codon is read. The amino acid chain is released and all of the translation machinery is recycled to translate another protein.

  43. Let’s put it all together • Click on the animation below Translation Animation Translation Video

  44. Let’s put it all together Coding: Template: mRNA: tRNA: amino acid: 5’-GATCTGAATCGCTATGGC-3’ 3’-CTAGACTTAGCGATACCG-5’ mRNA 5’-GAUCUGAAUCGCUAUGGC-3’ CUAGACUUAGCGAUACCG Asp, Leu, Asn, Arg, Tyr,Gly

  45. Control of Gene Expression

  46. Control of Gene Expression

  47. Control of Gene Expression • Prokaryotes cluster genes into operons that are transcribed together to give a single mRNA molecule.

  48. Control of Gene Expression • Lac Operon • Promoter region allows RNA polymerase to attach and begin transcription. • Operator region is in the middle of the promoter.

  49. Control of Gene Expression • If a repressor protein is bound to the operator, RNA polymerase cannot pass to transcribe the genes.

  50. Control of Gene Expression • When the inducer (lactose) binds to the repressor protein, it changes shape and falls off of the operator region. • Now RNA polymerase can pass and transcribe the genes into mRNA.

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