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  • Biology, 9th ed,Sylvia Mader DNA Structure & Function Slide # Chapter 13
  • Biology, 9th ed,Sylvia Mader DNA Structure & Function Slide # Chapter 13

12 Lecture Animation Ppt 12 Lecture Animation Ppt Presentation Transcript

  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b. 3.4 nm 2 nm 0.34 nm G C A T T A P P P P C G G C Complementary base pairing Sugar hydrogen bonds sugar-phosphate backbone
  • Outline
    • Genetic Material
      • Transformation
    • DNA Structure
      • Watson and Crick
    • DNA Replication
      • Prokaryotic versus Eukaryotic
      • Replication Errors
    • Transcription
    • Translation
    • Structure of Eukaryotic Chromosome
  • Genetic Material
    • Frederick Griffith investigated virulence of Streptococcus pneumoniae
      • Concluded that virulence passed from the dead strain to the living strain
      • Transformation
    • Further research by Avery et al.
      • Discovered that DNA is the transforming substance
      • DNA from dead cells was being incorporated into genome of living cells
  • Griffith’s Transformation Experiment
    • Mice were injected with two strains of pneumococcus: an encapsulated (S) strain and a non-encapsulated (R) strain.
      • The S strain is virulent (the mice died); it has a mucous capsule and forms “shiny” colonies.
      • The R strain is not virulent (the mice lived); it has no capsule and forms “dull” colonies.
  • Griffith’s Transformation Experiment Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. capsule Injected live S strain has capsule and causes mice to die. a. b. Injected live R strain has no capsule and mice do not die. c. Injected heat- killed S strain does not cause mice to die. d. Injected heat-killed S strain plus live R strain causes mice to die. Live S strain is withdrawn from dead mice.
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Transformation of Organisms Today
    • Result the so-called genetically modified organisms (GMOs)
      • Invaluable tool in modern biotechnology today
      • Commercial products that are currently much used
      • Green fluorescent protein (GFP) used as a marker
        • A jellyfish gene codes for GFP
        • The jellyfish gene is isolated and then transferred to a bacterium, or the embryo of a plant, pig, or mouse.
        • When this gene is transferred to another organism, the organism glows in the dark
  • Transformation of Organisms A normal canola plant (left) and a transgenic canola plant expressing GFP (right) under a fluorescent light. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. (Bacteria): © Martin Shields/Photo Researchers, Inc.; (Jellyfish): © R. Jackman/OSF/Animals Animals/Earth Scenes; (Pigs): Courtesy Norrie Russell, The Roslin Institute; (Mouse): © Eye of Science/Photo Researchers, Inc.; (Plant): © Dr. Neal Stewart
  • Structure of DNA
    • DNA contains:
      • Two Nucleotides with purine bases
        • Adenine (A)
        • Guanine (G)
      • Two Nucleotides with pyrimidine bases
        • Thymine (T)
        • Cytosine (C)
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Chargaff’s Rules
    • The amounts of A, T, G, and C in DNA:
      • Identical in identical twins
      • Varies between individuals of a species
      • Varies more from species to species
    • In each species, there are equal amounts of:
      • A & T
      • G & C
    • All this suggests DNA uses complementary base pairing to store genetic info
    • Human chromosome estimated to contain, on average, 140 million base pairs
    • Number of possible nucleotide sequences, 4,140,000,000
  • Nucleotide Composition of DNA Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. O N N CH CH C C NH 2 cytosine (C) 3 C C 2 C 1 O HO P O O H H H H H OH CH 3 O HN N C CH C C O HO P O O H H H H H OH HN N N C CH O C C C N H 2 N C 2 C 2 C 1 C 1 O HO P O O guanine (G) phosphate H H H H H OH N N N HC CH NH 2 C C C N 4 3 C 2 C 1 5 O O O O O O H H H H H OH c. Chargaf f ’ s data DN A Composition in V arious Species (%) Species Homo sapiens (human) Drosophila melanogaster (fruit fly) Zea mays (corn) Neurospora crassa (fungus) Escherichia coli (bacterium) Bacillus subtilis (bacterium) 31.0 27.3 25.6 23.0 24.6 28.4 31.5 27.6 25.3 23.3 24.3 29.0 19.1 22.5 24.5 27.1 25.5 21.0 18.4 22.5 24.6 26.6 25.6 21.6 A T G C a. Purine nucleotides b. Pyrimidine nucleotides nitrogen-containing base sugar = deoxyribose thymine (T) adenine (A) HO P O CH 2 5 CH 2 5 CH 2 5 CH 2 C 4 C 4 C 4 C C 3 C 3 C
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Watson and Crick Model
    • Watson and Crick, 1953
      • Constructed a model of DNA
      • Double-helix model is similar to a twisted ladder
        • Sugar-phosphate backbones make up the sides
        • Hydrogen-bonded bases make up the rungs
      • Received a Nobel Prize in 1962
  • Watson/Crick Model of DNA Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a: © Kenneth Eward/Photo Researchers, Inc.; d: © A. Barrington Brown/Photo Researchers, Inc. P P P P c. b. complementary base sugar-phosphate backbone 3.4 nm 2 nm 0.34 nm P P S S 4 5 end 3 end 1 1 2 3 2 3 5 4 5 C G G C C G T T A A C G a. d. d. 5 end sugar hydrogen bonds
  • X-Ray Diffraction of DNA
    • Rosalind Franklin studied the structure of DNA using X-rays.
    • She found that if a concentrated, viscous solution of DNA is made, it can be separated into fibers.
    • Under the right conditions, the fibers can produce X-ray diffraction pattern
      • She produced X-ray diffraction photographs.
      • This provided evidence that DNA had the following features:
        • DNA is a helix.
        • Some portion of the helix is repeated.
  • X-Ray Diffraction of DNA Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. © Photo Researchers, Inc.; c: © Science Source/Photo Researchers, Inc. X-ray beam b. c. Rosalind Franklin diffraction pattern Crystalline DNA diffracted X-rays a.
  • Replication of DNA
    • DNA replication is the process of copying a DNA molecule.
    • Replication is semiconservative , with each strand of the original double helix ( parental molecule) serving as a template (mold or model) for a new strand in a daughter molecule.
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Replication: Eukaryotic
    • DNA replication begins at numerous points along linear chromosome
    • DNA unwinds and unzips into two strands
    • Each old strand of DNA serves as a template for a new strand
    • Complementary base-pairing forms new strand on each old strand
      • Requires enzyme DNA polymerase
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Replication: Eukaryotic
    • Replication bubbles spread bi-directionally until they meet
    • The complementary nucleotides join to form new strands. Each daughter DNA molecule contains an old strand and a new strand.
    • Replication is semiconservative:
      • One original strand is conserved in each daughter molecule i.e. each daughter double helix has one parental strand and one new strand.
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Semiconservative Replication of DNA Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. region of parental DNA double helix G G G T A A C C 3' 5' A T C G A T A G G C C G A region of replication: new nucleotides are pairing with those of parental strands region of completed replication daughter DNA double helix old strand new strand daughter DNA double helix old strand new strand C C A A T T G G T A T A C G A T A T A C G A T A T A T A C G C G A G T A C G C G A
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Science Focus: Aspects of DNA Replication G C A T T G C G C A P P P P P P P P P P P P is attached here OH CH 2 C C C C H H H H H OH OH O base is attached here 5  end 3  end 5  end template strand Direction of replication new strand Deoxyribose molecule RNA primer 3  3  5  3  5  5  parental DN A helix helicase at replication fork leading new strand template strand template strand lagging strand DN A polymerase DNA polymerase DNA ligase Okazaki fragment Replication fork introduces complications 5 7 6 4 3 2 1 DNA polymerase attaches a new nucleotide to the 3 carbon of the previous nucleotide. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5  4  3  2  1  3  end 3 
  • Replication: Prokaryotic
    • Prokaryotic Replication
      • Bacteria have a single circular loop
      • Replication moves around the circular DNA molecule in both directions
      • Produces two identical circles
      • Cell divides between circles, as fast as every 20 minutes
  • Replication: Prokaryotic vs. Eukaryotic Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. origin replication is occurring in two directions replication is complete replication fork replication bubble a. Replication in prokaryotes parental strand daughter strand new DNA duplexes b. Replication in eukaryotes
  • Replication Errors
    • Genetic variations are the raw material for evolutionary change
    • Mutation:
      • A permanent (but unplanned) change in base-pair sequence
        • Some due to errors in DNA replication
        • Others are due to to DNA damage
      • DNA repair enzymes are usually available to reverse most errors
  • Function of Genes
    • Genes Specify Enzymes
      • Beadle and Tatum:
        • Experiments on fungus Neurospora crassa
        • Proposed that each gene specifies the synthesis of one enzyme
        • One-gene-one-enzyme hypothesis
    • Genes Specify a Polypeptide
      • A gene is a segment of DNA that specifies the sequence of amino acids in a polypeptide
      • Suggests that genetic mutations cause changes in the primary structure of a protein
  • Protein Synthesis: From DNA to RNA to Protein
    • The mechanism of gene expression
      • DNA in genes specify information, but information is not structure and function
      • Genetic info is expressed into structure & function through protein synthesis
    • The expression of genetic info into structure & function:
      • DNA in gene controls the sequence of nucleotides in an RNA molecule
      • RNA controls the primary structure of a protein
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • The Central Dogma of Molecular Biology Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. nontemplate strand 3' 5' A G G G A C C C C T C G C T G G G G 5' 3' template strand transcription in nucleus 3' 5' mRN DNA A G G G A C C C C codon 1 codon 2 codon 3 polypeptide translation at ribosome N N N C C C C C C R 1 R 2 R 3 Serine Aspartate Proline O O O
  • Types of RNA
    • RNA is a polymer of RNA nucleotides
    • RNA Nucleotides are of four types: Uracil, Adenine, Cytosine, and Guanine
    • Uracil (U) replaces thymine (T) of DNA
    • Types of RNA
        • Messenger (mRNA) - Takes genetic message from DNA in nucleus to ribosomes in cytoplasm
        • Ribosomal (rRNA) - Makes up ribosomes which read the message in mRNA
        • Transfer (tRNA) - Transfers appropriate amino acid to ribosome when “instructed”
  • Structure of RNA G U A C S S S S P P P P ribose G U base is uracil instead of thymine A C one nucleotide Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  • RNA vs. DNA structure
  • The Genetic Code
    • Properties of the genetic code:
      • Universal
        • With few exceptions, all organisms use the code the same way
        • Encode the same 20 amino acids with the same 64 triplets
      • Degenerate (redundant)
        • There are 64 codons available for 20 amino acids
        • Most amino acids encoded by two or more codons
      • Unambiguous (codons are exclusive)
        • None of the codons code for two or more amino acids
        • Each codon specifies only one of the 20 amino acids
      • Contains start and stop signals
        • Punctuation codons
        • Like the capital letter we use to signify the beginning of a sentence, and the period to signify the end
  • The Genetic Code
    • The unit of a code consists of codons, each of which is a unique arrangement of symbols
    • Each of the 20 amino acids found in proteins is uniquely specified by one or more codons
      • The symbols used by the genetic code are the mRNA bases
        • Function as “letters” of the genetic alphabet
        • Genetic alphabet has only four “letters” (U, A, C, G)
      • Codons in the genetic code are all three bases (symbols) long
        • Function as “words” of genetic information
        • Permutations:
          • There are 64 possible arrangements of four symbols taken three at a time
          • Often referred to as triplets
        • Genetic language only has 64 “words”
  • Messenger RNA Codons Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Second Base Third Base First Base U C G A U C A G UUU phenylalanine UCU serine UAU tyrosine UGU cysteine UUC phenylalanine UCC serine UAC tyrosine UGU cysteine UCA serine UUA leucine UCG serine UUG leucine UGG tryptophan UGA stop UAA stop UAG stop U C A G CUU leucine CUC leucine CUA leucine CUG leucine CCU proline CCC proline CCA proline CCG proline CAC histidine CAA glutamine CAG glutamine CAU histidine CGA arginine CGG arginine CGU arginine CGC arginine U C A G AUG ( start ) methionine AUU isoleucine AUC isoleucine AUA isoleucine ACU threonine ACC threonine ACA threonine ACG threonine AAU asparagine AAC asparagine AAA lysine AAG lysine AGU serine AGC serine AGA arginine AGG arginine U C A G GUU valine GUC valine GUA valine GUG valine GCU alanine GCC alanine GCA alanine GCG alanine GAU aspartate GAC aspartate GAA glutamate GAG glutamate GGU glycine GGC glycine GGA glycine GGG glycine U C A G
  • Steps in Gene Expression: Transcription
    • Transcription
      • Gene unzips and exposes unpaired bases
      • Serves as template for mRNA formation
      • Loose RNA nucleotides bind to exposed DNA bases using the C=G & A=U rule
      • When entire gene is transcribed into mRNA, result is a pre-mRNA transcript of the gene
      • The base sequence in the pre-mRNA is complementary to the base sequence in DNA
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Transcription of mRNA
    • A single chromosomes consists of one very long molecule encoding hundreds or thousands of genes
    • The genetic information in a gene describes the amino acid sequence of a protein
      • The information is in the base sequence of one side (the “sense” strand) of the DNA molecule
      • The gene is the functional equivalent of a “sentence”
    • The segment of DNA corresponding to a gene is unzipped to expose the bases of the sense strand
      • The genetic information in the gene is transcribed (rewritten) into an mRNA molecule
      • The exposed bases in the DNA determine the sequence in which the RNA bases will be connected together
      • RNA polymerase connects the loose RNA nucleotides together
    • The completed transcript contains the information from the gene, but in a mirror image, or complementary form
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Transcription Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. nontemplate strand template strand 5' C C G T A A T G C A A C G T C T C U G G A C C A C A T G G C RNA polymerase DNA template strand mRNA transcript C G C A T C G T A to RNA processing 3' 3' 5'
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • RNA Polymerase © Oscar L. Miller/Photo Researchers, Inc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. 200m b. spliceosome DNA RNA polymerase RNA transcripts
  • Processing Messenger RNA
    • Pre-mRNA, is modified before leaving the eukaryotic nucleus.
      • Modifications to ends of primary transcript:
        • Cap of modified guanine on 5′ end
          • The cap is a modified guanine (G) nucleotide
          • Helps a ribosome where to attach when translation begins
        • Poly-A tail of 150+ adenines on 3′ end
        • Facilitates the transport of mRNA out of the nucleus
        • Inhibits degradation of mRNA by hydrolytic enzymes.
  • Processing Messenger RNA
    • Pre-mRNA, is composed of exons and introns.
      • The exons will be ex pressed,
      • The introns, occur in between the exons.
        • Allows a cell to pick and choose which exons will go into a particular mRNA
      • RNA splicing:
        • Primary transcript consists of:
          • Some segments that will not be expressed (introns)
          • Segments that will be expressed (exons)
        • Performed by spliceosome complexes in nucleoplasm
          • Introns are excised
          • Remaining exons are spliced back together
    • Result is mature mRNA transcript
  • RNA Splicing
    • In prokaryotes, introns are removed by “self-splicing”—that is, the intron itself has the capability of enzymatically splicing itself out of a pre-mRNA
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Messenger RNA Processing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. exon intron intron exon exon DNA transcription exon intron intron exon exon 5' 3' pre-mRNA exon exon exon intron intron cap poly-A tail 5' 3' exon exon exon spliceosome cap poly-A tail pre-mRNA splicing intron RNA 5' 3' cap poly-A tail mRNA nuclear pore in nuclear envelope nucleus cytoplasm 5' 3'
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Functions of Introns
    • As organismal complexity increases;
      • Number of protein-coding genes does not keep pace
      • But the proportion of the genome that is introns increases
      • Humans:
        • Genome has only about 25,000 coding genes
        • Up to 95% of this DNA genes is introns
    • Possible functions of introns:
      • More bang for buck
        • Exons might combine in various combinations
        • Would allow different mRNAs to result from one segment of DNA
      • Introns might regulate gene expression
    • Exciting new picture of the genome is emerging
  • Steps in Gene Expression: Translation
    • tRNA molecules have two binding sites
      • One associates with the mRNA transcript
      • The other associates with a specific amino acid
      • Each of the 20 amino acids in proteins associates with one or more of 64 species of tRNA
    • Translation
      • An mRNA transcript migrates to rough endoplasmic reticulum
      • Associates with the rRNA of a ribosome
      • The ribosome “reads” the information in the transcript
      • Ribosome directs various species of tRNA to bring in their specific amino acid “fares”
      • tRNA specified is determined by the code being translated in the mRNA transcript
  • tRNA
    • tRNA molecules come in 64 different kinds
    • All very similar except that
      • One end bears a specific triplet (of the 64 possible) called the anticodon
      • Other end binds with a specific amino acid type
      • tRNA synthetases attach correct amino acid to the correct tRNA molecule
    • All tRNA molecules with a specific anticodon will always bind with the same amino acid
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Structure of tRNA Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. amino acid leucine 3 5 Hydrogen bonding anticodon mRNA 5' codon 3' b. anticodon end amino acid end
  • Ribosomes
    • Ribosomal RNA (rRNA):
      • Produced from a DNA template in the nucleolus
      • Combined with proteins into large and small ribosomal subunits
    • A completed ribosome has three binding sites to facilitate pairing between tRNA and mRNA
      • The E (for exit) site
      • The P (for peptide) site, and
      • The A (for amino acid) site
  • Ribosomal Structure and Function Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Courtesy Alexander Rich large subunit small subunit a. Structure of a ribosome tRNA binding sites outgoing tRNA 3 5 mRNA b. Binding sites of ribosome polypeptide incoming tRNA incoming tRNA c. Function of ribosomes d. Polyribosome
  • Steps in Translation: Initiation
    • Components necessary for initiation are:
      • Small ribosomal subunit
      • mRNA transcript
      • Initiator tRNA, and
      • Large ribosomal subunit
      • Initiation factors (special proteins that bring the above together)
    • Initiator tRNA:
      • Always has the UAC anticodon
      • Always carries the amino acid methionine
      • Capable of binding to the P site
  • Steps in Translation: Initiation
    • Small ribosomal subunit attaches to mRNA transcript
      • Beginning of transcript always has the START codon (AUG)
    • Initiator tRNA (UAC) attaches to P site
    • Large ribosomal subunit joins the small subunit
  • Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
  • Steps in Translation: Initiation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A small ribosomal subunit binds to mRNA; an initiator tRNA pairs with the mRNA start codon AUG. The large ribosomal subunit completes the ribosome. Initiator tRNA occupies the P site. The A site is ready for the next tRNA. Initiation Met amino acid methionine initiator tRNA U A C A U G mRNA small ribosomal subunit 3' 5' P site A site E site Met large ribosomal subunit U A C A U G start codon 5' 3'
  • Steps in Translation: Elongation
    • “ Elongation” refers to the growth in length of the polypeptide
    • RNA molecules bring their amino acid fares to the ribosome
      • Ribosome reads a codon in the mRNA
        • Allows only one type of tRNA to bring its amino acid
        • Must have the anticodon complementary to the mRNA codon being read
        • Joins the ribosome at it’s A site
      • Methionine of initiator is connected to amino acid of 2 nd tRNA by peptide bond
  • Steps in Translation: Elongation
    • Second tRNA moves to P site (translocation)
    • Spent initiator moves to E site and exits
    • Ribosome reads the next codon in the mRNA
      • Allows only one type of tRNA to bring its amino acid
        • Must have the anticodon complementary to the mRNA codon being read
        • Joins the ribosome at it’s A site
      • Dipeptide on 2 nd amino acid is connected to amino acid of 3 nd tRNA by peptide bond
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  • Steps in Translation: Elongation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A tRNA–amino acid approaches the ribosome and binds at the A site. Two tRNAs can be at a ribosome at one time; the anticodons are paired to the codons. Peptide bond formation attaches the peptide chain to the newly arrived amino acid. The ribosome moves forward; the “ empty” tRNA exits from the E site; the next amino acid–tRNA complex is approaching the ribosome. 1 2 3 4 Elongation peptide bond Met Ala Trp Ser Val U A C A U G G A C 3 3 C G anticodon tRNA asp U Met Ala Trp Ser Val U A C A U G G A C C U G Asp 6 U A C A U G G A C C U G Met Val Asp Ala Trp Ser peptide bond 6 3 U C A G A C C U G A U G U G G A C C Met Val Asp Ala Trp Ser Thr 6 3
  • Steps in Translation: Termination
    • Previous tRNA moves to P site
    • Spent tRNA moves to E site and exits
    • Ribosome reads the STOP codon at the end of the mRNA
      • UAA, UAG, or UGA
      • Does not code for an amino acid
    • Polypeptide is released from last tRNA by release factor
    • Ribosome releases mRNA and dissociates into subunits
    • mRNA read by another ribosome
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  • Steps in Translation: Termination Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Termination The release factor hydrolyzes the bond between the last tRNA at the P site and the polypeptide, releasing them. The ribosomal subunits dissociate. 3 5 A G A U G A The ribosome comes to a stop codon on the mRNA. A release factor binds to the site. U A U A U G A stop codon 5' 3' Asp Ala Trp Val Glu release factor Ala Trp V al Asp Glu U C U
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  • Summary of Gene Expression (Eukaryotes) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. TRANSCRIPTION 1. DNA in nucleus serves as a template for mRNA. 2. mRNA is processed before leaving the nucleus. mRNA pre-mRNA DNA introns 3. mRNA moves into cytoplasm and becomes associated with ribosomes. TRANSLATION mRNA large and small ribosomal subunits 3' nuclear pore 4. tRNAs with anticodons carry amino acids to mRNA. 5 peptide codon ribosome 3 U A A U C G 5 C C G G G C G C G C C C C G U A U A U A U U A A 6. During elongation, polypeptide synthesis takes place one amino acid at a time. 7. Ribosome attaches to rough ER. Polypeptide enters lumen, where it folds and is modified. 8. During termination, a ribosome reaches a stop codon; mRNA and ribosomal subunits disband. 5. During initiation, anticodon-codon complementary base pairing begins as the ribosomal subunits come together at a start codon. amino acids anticodon tRNA C U A 3' 5
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  • Structure of Eukaryotic Chromosome
    • Contains a single linear DNA molecule, but is composed of more than 50% protein.
    • Some of these proteins are concerned with DNA and RNA synthesis,
    • Histones , play primarily a structural role
      • Five primary types of histone molecules
      • Responsible for packaging the DNA
        • DNA double helix is wound at intervals around a core of eight histone molecules (called nucleosome)
        • Nucleosomes are joined by “linker” DNA.
  • Structure of Eukaryotic Chromosome Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Nucleosomes (“beads on a string”) b. 30-nm fiber c. Radial loop domains d. Heterochromatin e. Metaphase chromosome 1. Wrapping of DNA around histone proteins. 4. Tight compaction of radial loops to form heterochromatin. 3. Loose coiling into radial loops. 2. Formation of a three-dimensional zigzag structure via histone H1 and other DNA-binding proteins. 5. Metaphase chromosome forms with the help of a protein scaffold. 2 nm 1 nm 300 nm 1,400 nm 700 nm 30 nm DNA double helix histones histone H1 nucleosome euchromatin
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  • Review
    • Genetic Material
      • Transformation
    • DNA Structure
      • Watson and Crick
    • DNA Replication
      • Prokaryotic versus Eukaryotic
      • Replication Errors
    • Transcription
    • Translation
    • Structure of Eukaryotic Chromosome
  • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. b. 3.4 nm 2 nm 0.34 nm G C A T T A P P P P C G G C Complementary base pairing Sugar hydrogen bonds sugar-phosphate backbone