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Chapter 10

Chapter 10. 0. Molecular Biology of the Gene. Original DNA sequence: TAC ACC TTG GCG ACG ACT mRNA: tRNA: A.A.:. Sugar-phosphate backbone. Phosphate group. Nitrogenous base. A. A. Sugar. Nitrogenous base (A, G, C, or T). Phosphate group. C. C.

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Chapter 10

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  1. Chapter 10 0 Molecular Biology of the Gene

  2. Original DNA sequence: • TAC ACC TTG GCG ACG ACT • mRNA: • tRNA: • A.A.:

  3. Sugar-phosphate backbone Phosphate group Nitrogenous base A A Sugar Nitrogenous base(A, G, C, or T) Phosphategroup C C DNA nucleotide O H H3C C C N O C C T CH2 H T O P N O O O– Thymine (T) O C C H H H H G G C C H O Sugar(deoxyribose) T T DNA nucleotide DNA polynucleotide • 10.2 DNA and RNA are polymers of nucleotides • DNA is a nucleic acid • Made of long chains of nucleotide monomers Figure 10.2A

  4. H H H H O N N O C H C H H3C C C H N N N C C N C N N C H H C C C C C C C C C C H O H N N N O H N N H N N H H H H H Adenine (A) Guanine (G) Thymine (T) Cytosine (C) Purines Pyrimidines • DNA has four kinds of nitrogenous bases • A, T, C, and G Figure 10.2B

  5. Nitrogenous base (A, G, C, or U) Key Hydrogen atom O Phosphategroup Carbon atom C H Nitrogen atom H N C Oxygen atom O C C Phosphorus atom H O P O CH2 O N Uracil (U) O– O C C H H H H C C OH O Sugar(ribose) • RNA is also a nucleic acid • But has a slightly different sugar • And has U instead of T Figure 10.2C, D

  6. 10.3 DNA is a double-stranded helix • James Watson and Francis Crick • Worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin Figure 10.3A, B

  7. Twist • The structure of DNA • Consists of two polynucleotide strands wrapped around each other in a double helix Figure 10.3C

  8. G C O T A OH P Hydrogen bond –O O A T OH O H2C A T Basepair O CH2 O O C G P O O– –O C G O P O H2C O O C T G A O CH2 C G O O P O O– – O O P O H2C O O G C A T O CH2 O O A T P O – O O– O P A T O O H2C O A T A T CH2 O OH O O– P G C HO O T A Partial chemical structure Ribbon model Computer model • Hydrogen bonds between bases • Hold the strands together • Each base pairs with a complementary partner • A with T, and G with C Figure 10.3D

  9. DNA and RNA are identical except for two things: • Nitrogenous bases • DNA: A, C, G, T • RNA: A, G, C, U • Sugars • DNA: deoxyribose • RNA: ribose Animation: DNA and RNA Structure

  10. T A T T A A T A T A G C G G G C C C G C C C G G G C G C C A A T A T A A T T A T T T A A A T Both parental strands serve as templates Two identical daughtermolecules of DNA Parental moleculeof DNA DNA REPLICATION • 10.4 DNA replication depends on specific base pairing • DNA replication • Starts with the separation of DNA strands • Then enzymes use each strand as a template • To assemble new nucleotides into complementary strands Nucleotides Figure 10.4A

  11. G C T A G C G C A T T A C G A T C G G C C G G C C C G G A C A T A T T G A T T G T T A A A A A C T T T A • DNA replication is a complex process • Due in part to the fact that some of the helical DNA molecule must untwist Figure 10.4B

  12. 10.5 DNA replication: A closer look • DNA replication begins at specific sites (origins of replication) on the double helix • Proteins (such as enzyme helicase) attach and separate the strands • Replication proceeds in both directions, creating replication bubbles • Parent strands open, daughter strands elongate • Replication occurs simultaneously at many sites

  13. Parental strand Origin of replication Daughter strand Bubble Two daughter DNA molecules Figure 10.5A

  14. 5 end 3 end P HO 5 4 2 3 A T 3 1 1 4 2 5 P P C G P P G C P P A T OH P 3 end 5 end • Each strand of the double helix • Is oriented in the opposite direction Figure 10.5B

  15. DNA polymerase molecule 3 5 Daughter strandsynthesizedcontinuously Parental DNA 5 3 Daughter strandsynthesizedin pieces 3 5 5 3 DNA ligase Overall direction of replication • Using the enzyme DNA polymerase • The cell synthesizes one daughter strand as a continuous piece • The other strand is synthesized as a series of short pieces • Which are then connected by the enzyme DNA ligase Figure 10.5C

  16. DNA's sugar-phosphate backbones are oriented in opposite directions • The enzyme DNA polymerase adds nucleotides at only the 3’ end so the new strand is built in the 5’  3’direction • One daughter strand is synthesized as a continuous piece = leading strand • The other strand is synthesized as a series of short pieces = lagging strands (AKA Okazaki fragments) • The lagging strands are connected by the enzyme DNA ligase

  17. DNA REPLICATON SUMMARY

  18. THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN • 10.6 The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits • The information constituting an organism’s genotype • Is carried in its sequence of its DNA bases • A particular gene, a linear sequence of many nucleotides • Specifies a polypeptide

  19. DNA Transcription RNA Translation Protein Figure 10.6A • The DNA of the gene is transcribed into RNA • Which is translated into the polypeptide

  20. The flow of genetic information (2 stages) • Transcription of the genetic information in DNA into RNA (DNA  RNA) – occurs in the nucleus • Translation of RNA into the polypeptide (RNA  proteins) – occurs on the ribosome either in the cytoplasm or attached to the rough e.r.

  21. 10.7 Genetic information written in codons is translated into amino acid sequences • The “words” of the DNA “language” • Are triplets of bases called codons • The codons in a gene • Specify the amino acid sequence of a polypeptide

  22. DNA molecule Gene 1 Gene 2 Gene 3 DNA strand A A A C A C G G A A C A Transcription U U U G U G C C U U G U RNA Codon Translation Polypeptide Amino acid Figure 10.7

  23. Second base U C A G U UAU UGU UGC UGA Stop UUU UCU Cys Phe Tyr UUC UAC C UCC Ser U UCA UUA UAA Stop A Leu UCG UAG Stop UGG Trp G U CAU CGU CUU CCU His C CAC CGC CUC CCC C Pro Arg Leu CUA CCA CAA CGA A Gln CAG CGG CUG CCG G Third base First base U ACU AUU AAU AGU Ser Asn ACC AGC AUC AAC Ile C A Thr AUA AGA ACA AAA A Lys Arg Met or start ACC AGG AAG AUG G U GUU GAU GGU GCU Asp C GGC GCC GUC GAC Gly Ala G Val GUA GCA GGA GAA A Glu GUG GCG GGG GAG G Figure 10.8A • 10.8 The genetic code is the Rosetta stone of life • Nearly all organisms use exactly the same genetic code UUG

  24. Strand to be transcribed T A C T T C A A A A T C DNA A T G A A G T T T T A G Transcription G U U U A G A U A A G U RNA Startcondon Stopcondon Translation Met Polypeptide Lys Phe Figure 10.8B • An exercise in translating the genetic code

  25. 10.9 Transcription produces genetic messages in the form of RNA • One DNA strand serves as a template for the new RNA strand • RNA polymerase constructs the RNA strand in a multistep process • Initiation • RNA polymerase attaches to the promotor • Synthesis starts

  26. Elongation: • RNA synthesis continues as RNA polymerase brings in complementary RNA nucleotides • RNA strand peels away from DNA template • DNA strands come back together in transcribed region • Termination • RNA polymerase reaches a terminator sequence at the end of the gene • Polymerase detaches

  27. LE 10-9a RNA nucleotides RNA polymerase C C A A T T A U T C T G U G A C A C U C A C C A G A T T G T G A Direction of transcription Template strand of DNA Newly made RNA

  28. LE 10-9b RNA polymerase DNA of gene Promoter DNA Terminator DNA Initiation Initiation Area shown In Figure 10.9A Elongation Growing RNA Termination Completed RNA RNA polymerase

  29. THREE TYPES OF RNA • Messenger RNA = mRNA holds the genetic code (contains the codons) and is “read” by the ribosome to make proteins • Transfer RNA = tRNA  carries (transfers) the correct amino acid to the ribosome • Ribosomal RNA = rRNA  combines with other proteins to make ribosomes

  30. See transcription animation! http://www.youtube.com/watch?feature=endscreen&v=ztPkv7wc3yU&NR=1&safety_mode=true&persist_safety_mode=1&safe=active http://www.youtube.com/watch?v=SMtWvDbfHLo&safety_mode=true&persist_safety_mode=1&safe=active http://www.youtube.com/watch?v=NJxobgkPEAo&feature=related&safety_mode=true&persist_safety_mode=1&safe=active http://www.youtube.com/watch?v=983lhh20rGY&safety_mode=true&persist_safety_mode=1&safe=active

  31. 10.10 Eukaryotic RNA is processed before leaving the nucleus • RNA PROCESSING: • Doesn’t occur in prokaryotes because prokaryotes use all of their DNA • In eukaryotes, RNA transcribed in the nucleus is processed before moving to the cytoplasm for translation

  32. Steps to RNA Processing: • Noncoding segments called introns are cut out • Remaining exons are joined to form a continuous coding sequence • A 5’cap and a 3’ polyA-tail are added to the ends of the mRNA

  33. Exon Intron Exon Intron Exon DNA Transcription Addition of cap and tail Cap RNA transcript with cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence Nucleus Cytoplasm Figure 10.10 • 10.10 Eukaryotic RNA is processed before leaving the nucleus • Noncoding segments called introns are spliced out • And a cap and a tail are added to the ends

  34. 10.11 Transfer RNA molecules serve as interpreters during translation • Translation • Takes place in the cytoplasm

  35. 0 Amino acid attachment site Hydrogen bond RNA polynucleotide chain Anticodon Figure 10.11A • A ribosome attaches to the mRNA • And translates its message into a specific polypeptide aided by transfer RNAs (tRNAs)

  36. Amino acid attachment site Anticodon Figure 10.11B, C • Each tRNA molecule • Is a folded molecule bearing a base triplet called an anticodon on one end • A specific amino acid • Is attached to the other end

  37. tRNAmolecules Growingpolypeptide Largesubunit mRNA Small subunit Figure 10.12A • 10.12 Ribosomes build polypeptides • A ribosome consists of two subunits • Each made up of proteins and a kind of RNA called ribosomal RNA

  38. The subunits of a ribosome • Hold the tRNA and mRNA close together during translation tRNA-binding sites Largesubunit Next amino acid to be added to polypeptide Growing polypeptide tRNA mRNA-binding site mRNA Smallsubunit Codons Figure 10.12B, C

  39. Start of genetic message End Figure 10.13A • 10.13 An initiation codon marks the start of an mRNA message

  40. Large ribosomalsubunit Met Met Initiator tRNA P site A site U C U A C A A U G AUG Startcodon Small ribosomalsubunit mRNA 1 2 Figure 10.13B • mRNA, a specific tRNA, and the ribosome subunits • Assemble during initiation

  41. 10.14 Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation • Once initiation is complete • Amino acids are added one by one to the first amino acid

  42. 1 Codon recognition 2 Peptide bondformation Translocation 3 • Each addition of an amino acid • Occurs in a three-step elongation process Aminoacid Polypeptide P site A site Anticodon mRNA Codons mRNAmovement Stopcodon New Peptidebond Figure 10.14

  43. The mRNA moves a codon at a time • And a tRNA with a complementary anticodon pairs with each codon, adding its amino acid to the peptide chain

  44. Elongation continues • Until a stop codon reaches the ribosome’s A site, terminating translation

  45. 10.15 Review: The flow of genetic information in the cell is DNARNAprotein • The sequence of codons in DNA, via the sequence of codons • Spells out the primary structure of a polypeptide

  46. 1     mRNA is transcribed from a DNA template. 2      Each amino acidattaches to its propertRNA with the help of aspecific enzyme and ATP. 3       Initiation ofpolypeptide synthesis The mRNA, the first tRNA, and the ribosomal subunits come together. 4 Elongation A succession of tRNAsadd their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time. 5 Termination The ribosome recognizes a stop codon. The poly-peptide is terminated and released. • Summary of transcription and translation DNA Transcription mRNA RNApolymerase Amino acid Translation Enzyme ATP tRNA Anticodon Largeribosomal subunit InitiatortRNA Start Codon Smallribosomal subunit mRNA New peptidebond forming Growingpolypeptide Codons mRNA Polypeptide Figure 10.15 Stop codon

  47. Normal hemoglobin DNA Mutant hemoglobin DNA C A T T T C mRNA mRNA G A A G U A Normal hemoglobin Sickle-cell hemoglobin Glu Val Figure 10.16A • 10.16 Mutations can change the meaning of genes • Mutations are changes in the DNA base sequence • Caused by errors in DNA replication or recombination, or by mutagens

  48. Normal gene U G C U U C A G A A U G A G G mRNA Met Lys Gly Protein Phe Ala Base substitution A A G A U G C A U G A G U U C Lys Met Phe Ser Ala Missing U Base deletion G G C G A C A U A U G A G U U Figure 10.16B Lys Ala His Met Leu • Substituting, inserting, or deleting nucleotides alters a gene • With varying effects on the organism

  49. Envelope Glycoprotein Protein coat RNA (two identical strands) Reverse transcriptase Figure 10.21A • 10.21 The AIDS virus makes DNA on an RNA template • HIV, the AIDS virus • Is a retrovirus

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