1 The Interrupted Gene. Ex Biochem c3-interrupted gene 2 3.1 Introduction Figure 3.1

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Transcript of 1 The Interrupted Gene. Ex Biochem c3-interrupted gene 2 3.1 Introduction Figure 3.1

  • *The Interrupted Gene

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*3.1 IntroductionFigure 3.1

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*3.2 An Interrupted Gene Consists of Exons and IntronsIntrons are removed by the process of RNA splicingOnly mutations in exons can affect protein sequence; however, mutations in introns can affect processing of the RNA, preventing production of protein.Figure 3.2

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*3.3 Restriction Endonucleases: Key Tool in Mapping DNARestriction endonucleases can be used to cleave DNA into defined fragments.Only cut DNA with specific sequenceRestriction enzyme Figure 3.3

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*A map can be generated by using the overlaps between the fragments generated by different restriction enzymes.Figure 3.4Restriction map

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*3.4 Organization of Interrupted Genes May Be ConservedIntrons can be detected by the presence of additional regions when genes are compared with their RNA products by restriction mapping or electron microscopy. Complimentary DNA (cDNA)Ultimate definition is based on comparison of sequences.Figure 3.5

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*The positions of introns are usually conserved when homologous genes are compared between different organisms.The lengths of the corresponding introns may vary greatly.Introns usually do not code for proteins.Figure 3.7

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*3.5 Exon Sequences Are Conserved but Introns VaryComparisons of related genes in different species show that the sequences of the corresponding exons are usually conserved;but the sequences of the introns are much less well relatedFigure 3.9

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*Exons are usually short, typically coding for
  • Ex Biochem c3-interrupted gene*The overall length of a gene is determined largely by its introns.Figure 3.13

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*3.7 Some DNA Sequences Code for More Than One ProteinThe use of alternative initiation or termination codons allows two proteins to be generated where one is equivalent to a fragment of the other.Figure 3.14

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*when it is read in different reading frames by two (overlapping) genes.Figure 3.15Nonhomologous protein can be produced from same sequence of DNA

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*Homologous proteins can differ by the presence or absence of certain regions They are generated by differential (alternative) splicing when certain exons are included or excluded.This may take the form of:including or excluding individual exons choosing between alternative exonsFigure 3.17

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*Figure 3.19

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*3.9 Some Exons Can Be Equated with Protein Functionsexons were the building blocks of evolution and the first genes were interruptedGene structure is conserved between genes in very distant speciesMany exons can be equated with coding for protein sequences that have particular functions. Related exons are found in different genes.

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*Figure 3.20

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*3.10 Members of a Gene Family Have Common OrganizationA common feature in a set of genes is assumed to identify a property that preceded their separation in evolution.All globin genes have a common form of organization with three exons and two introns;This suggests that they are descended from a single ancestral gene.Figure 3.21

    Ex Biochem c3-interrupted gene

  • Ex Biochem c3-interrupted gene*

    Ex Biochem c3-interrupted gene