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The Molecular Basis of Inheritance

The Molecular Basis of Inheritance. Chapter 14. LEARNING OBJECTIVE 1. Distinguish between a chromosome and a gene. KEY TERMS. CHROMOSOME One of several rod-shaped bodies in the cell nucleus that contain hereditary units (genes) GENE

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The Molecular Basis of Inheritance

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  1. The Molecular Basis of Inheritance Chapter 14

  2. LEARNING OBJECTIVE 1 • Distinguish between a chromosome and a gene

  3. KEY TERMS • CHROMOSOME • One of several rod-shaped bodies in the cell nucleus that contain hereditary units (genes) • GENE • A discrete unit of hereditary information that usually specifies a polypeptide (protein)

  4. A Eukaryotic Chromosome

  5. 1400 nm 300 nm 30 nm Condensed chromosome Condensed chromatin Extended chromatin DNA wound around a cluster of histone molecules Bases 11 nm Sugar-phosphate backbone 2 nm DNA double helix Fig. 14-1, p. 276

  6. LEARNING OBJECTIVE 2 • Name the units that compose the DNA molecule • Identify the three parts of each unit

  7. DNA • Deoxyribonucleic acid molecule • A double helix • Each strand is composed of nucleotides

  8. A Nucleotide • Consists of • a sugar (deoxyribose) • a phosphate group • an organic base • Four DNA bases: • Cytosine, thymine, adenine, guanine

  9. DNA Structure

  10. Two sugar–phosphate backbones G C S S P P T A S G C S T A Paired bases A T P P C G A T S S A T C P G P C G G C A T S S Region of hydrogen bonding (b) A small portion of the DNA molecule is unwound to show complementary base pairing. (P = phosphate group; S = the sugar deoxyribose; G = guanine; C = cytosine; T = thymine; A = adenine) (a) DNA is a double helix consisting of two sugar– phosphate backbones joined by their paired bases. Fig. 14-2, p. 277

  11. LEARNING OBJECTIVE 3 • Describe base pairing in DNA molecules • Given the base sequence of one strand of DNA, predict that of a complementary strand of DNA

  12. Base Pairing • The two strands of the DNA double helix are joined by hydrogen bonds between complementary bases • Adenine pairs with thymine • Cytosine pairs with guanine

  13. LEARNING OBJECTIVE 4 • Summarize the process of DNA replication • Explain what is meant by “semiconservative replication”

  14. DNA Replication 1 • The process of making an exact copy of a DNA molecule • DNA strands unwind during replication

  15. DNA Replication 2 • DNA synthesis takes place at replication forks • Y-shaped regions where the two strands of DNA separate and where DNA synthesis occurs on both strands at once

  16. KEY TERMS • DNA POLYMERASE • Enzyme complex that catalyzes DNA replication by adding nucleotides to a growing strand of DNA

  17. KEY TERMS • SEMICONSERVATIVE REPLICATION • Type of replication characteristic of DNA • Each new double-stranded molecule consists of one strand from the original DNA molecule and one strand of newly synthesized DNA

  18. DNA Replication

  19. Backbones containing alternating sugar and phosphate (b) The two strands are shown separating, and both are being copied. In the new strand, as in the old, adenine pairs with thymine, and cytosine pairs with guanine. Fig. 14-3b, p. 279

  20. Replication Forks

  21. Replication fork Fig. 14-4, p. 280

  22. LEARNING OBJECTIVE 5 • Compare the structures of DNA and RNA molecules • Identify the functions of the three types of RNA: messenger RNA, transfer RNA, and ribosomal RNA

  23. RNA • Ribonucleic acid (RNA) is formed from nucleotide subunits • a sugar (ribose) • a phosphate group • a base (cytosine, guanine, adenine, uracil) • RNA is a single strand (unlike DNA) • although it may be elaborately folded

  24. RNA Structure

  25. KEY TERMS • MESSENGER RNA (mRNA) • Specifies amino acid sequence of a polypeptide • TRANSFER RNA (tRNA) • Transfers amino acids to the ribosome during protein synthesis

  26. KEY TERMS • RIBOSOMAL RNA (rRNA) • An important part of the structure of ribosomes • Also has catalytic functions needed during protein synthesis

  27. DNA and RNA

  28. LEARNING OBJECTIVE 6 • Outline the flow of genetic information in cells from DNA to protein • Summarize the processes of transcription and translation

  29. Protein Synthesis • DNA directs protein synthesis through an intermediary (RNA) • The flow of genetic information is from DNA to RNA to proteins

  30. KEY TERMS • TRANSCRIPTION • Synthesis of RNA from a DNA template • RNA POLYMERASE • Enzyme that catalyzes the synthesis of RNA molecules from DNA templates

  31. KEY TERMS • TRANSLATION • Conversion of information provided by RNA to a specific sequence of amino acids in the production of a polypeptide chain • Requires codons and anticodons

  32. KEY TERMS • CODON • A sequence of three nucleotides in mRNA that specifies an individual amino acid or a start or stop signal • ANTICODON • A sequence of three nucleotides in tRNA that is complementary to a specific codon in mRNA

  33. Overview: Protein Synthesis

  34. DNA TRANSCRIPTION mRNA Nucleus Cytoplasm Protein Ribosome mRNA TRANSLATION Fig. 14-6, p. 283

  35. Overview: Transcription

  36. RNA polymerase binds to promoter region in DNA DNA Termination sequence Promoter region Initiation. RNA polymerase unwinds DNA double helix and initiates RNA synthesis at promoter region. 1 1 Direction of transcription DNA template strand RNA 2 Elongation. Additional nucleotides are added to the RNA molecule. DNA double helix re-forms Following transcription. 2 Rewinding of DNA Unwinding of DNA 3 Termination. RNA polymerase recognizes termination sequence. RNA molecule and RNA polymerase are released. 3 DNA Completed RNA RNA polymerase Fig. 14-7, p. 284

  37. RNA polymerase binds to promoter region in DNA Termination sequence Promoter region Initiation. RNA polymerase unwinds DNA double helix and initiates RNA synthesis at promoter region. 1 1 DNA template strand RNA 2 Elongation. Additional nucleotides are added to the RNA molecule. DNA double helix re-forms Following transcription. 2 Rewinding of DNA Unwinding of DNA 3 Termination. RNA polymerase recognizes termination sequence. RNA molecule and RNA polymerase are released. 3 Completed RNA RNA polymerase DNA Direction of transcription DNA Stepped Art Fig. 14-7, p. 284

  38. Translation • Each tRNA molecule attaches to a specific amino acid and carries it to the ribosome • Ribosome recognizes anticodon of tRNA molecule • allows it to base-pair with mRNA codon

  39. Polypeptide Formation • The amino acid carried by tRNA forms a peptide bond with the growing polypeptide chain • The tRNA molecule is released, and the process is repeated

  40. tRNA Molecule

  41. Amino acid accepting end Loop 3 Amino acid (phenylalanine) Hydrogen bonds Loop 3 Loop 1 Loop 1 Modified nucleotides Loop 2 Loop 2 Anticodon Anticodon Anticodon (a) The 3-D shape of a tRNA molecule is determined by hydrogen bonds formed between complementary bases. (b) One loop contains the anticodon; these unpaired bases pair with a complementary mRNA codon. The amino acid attaches to the terminal nucleotide at the opposite end of the tRNA molecule. (c) This stylized diagram of an aminoacyl-tRNA shows that the amino acid attaches to tRNA by its carboxyl group, leaving its amino group exposed for peptide bond formation. Fig. 14-9, p. 286

  42. Overview: Translation

  43. Fig. 14-10a, p. 287

  44. Initiation (steps 1 and 2) Amino acid Large ribosomal subunit tRNA mRNA Small ribosomal subunit Start codon 1 The tRNA binds to the start codon by complementary base pairing between the tRNA’s anticodon and the mRNA’s codon. 2 When the large ribosomal subunit binds to the small subunit, initiation is complete. Fig. 14-10a, p. 287

  45. Fig. 14-10b, p. 287

  46. Elongation (steps 3 , 4,and 5) Polypeptide New peptide bond Amino acids 3 An aminoacyl-tRNA binds to mRNA by complementary base pairing between the anticodon and the codon. 4 The growing polypeptide chain becomes attached by a peptide bond to the amino acid that linked to mRNA in step 3. 5 The ribosome moves one codon to the right. The tRNA that gave up the growing polypeptide chain exits the ribosome. Elongation continues until a stop codon is reached. Fig. 14-10b, p. 287

  47. Fig. 14-10c, p. 287

  48. Termination (steps 6 and 7) Large ribosomal subunit Newly synthesized protein E Release factor P A Release factor mRNA Small ribosomal subunit Stop codon tRNA 6 When the ribosome reaches a stop codon, a protein release factor attaches to the stop codon. 7 The polypeptide chain is released, and the remaining parts of the translation complex separate. Fig. 14-10c, p. 287

  49. LEARNING OBJECTIVE 7 • Explain the universality of the genetic code and its evolutionary significance

  50. Genetic Code • Genetic code is nearly universal throughout the biological world • Same DNA triplets code for same amino acids in all organisms (only a few minor variations) • Universality is compelling evidence that all organisms evolved from same early life-forms

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