Gene expression
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Gene Expression. Early evidence indicating most genes specify the structure of proteins Garrod’s work on inborn errors of metabolism in early 1900s Beadle and Tatum’s work with Neurospora mutants in the 1940s. An “inborn error of metabolism”. Mutations affecting biochemical pathways.

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Gene Expression

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Gene expression

Gene Expression


Gene expression

  • Early evidence indicating most genes specify the structure of proteins

    • Garrod’s work on inborn errors of metabolism in early 1900s

    • Beadle and Tatum’s work with Neurospora mutants in the 1940s


Gene expression

An“inborn errorof metabolism”


Gene expression

Mutationsaffectingbiochemical

pathways


Gene expression

  • Information flow from DNA to protein

    • Transcription

      • RNA molecule complementary to the template DNA strand synthesized

    • Translation

      • Polypeptide chain specified by messenger RNA (mRNA) is synthesized


Gene expression

Nucleotidestructure of

RNA


Gene expression

Overview of transcription and translation


Gene expression

  • Structure of RNA

    • RNA

      • Formed from nucleotide subunits

      • Each nucleotide subunit contains ribose, a base, and three phosphates

      • Like DNA, RNA subunits are covalently joined by a 5΄—3΄ linkage to form alternating sugar-phosphate backbone


Gene expression

  • Transcription

    • Incoming nucleotides with three phosphates pair with complementary bases on the DNA strand

    • RNA polymerase cleaves two phosphates from each nucleotide and covalently links the remaining phosphate to the 3΄end of the RNA chain


Gene expression

Transcription


Gene expression

Synthesis of mRNA


Gene expression

  • Translation

    • Polypeptide chain specified by the mRNA is synthesized

      • Initiation

      • Repeating cycles of elongation

      • Termination

    • Each sequence of three nucleotide bases in the mRNA constitutes a codon

    • Requires tRNAs and cell machinery, including ribosomes


Gene expression

Three representations of a tRNA molecule


Gene expression

Ribosomestructure


Gene expression

Initiation of translation in bacteria


Gene expression

Elongation cycle in translation


Gene expression

Termination of translation


Gene expression

  • Coupled transcription and translation in bacteria

    • Unlike eukaryotic cells, in bacterial cells translation and transcription coupled

    • Translation of the bacterial mRNA molecule usually begins before the 3´ end of the transcript is completed


Gene expression

Coupled transcription and transla-tion in bacteria


Gene expression

  • Retroviruses

    • Flow of genetic information is reversed by reverse transcriptase

      • Enzyme associated with retroviruses

      • Retroviruses synthesize DNA from an RNA template

      • Example of retrovirus is HIV-1, AIDS virus


Gene expression

Infection cycle of an RNA tumor virus


Gene expression

  • Mutations

    • Base substitution mutations

      • Often result from errors in base pairing during replication

      • Missense mutations

      • Nonsense mutations

    • Frameshift mutations

      • One or two nucleotide pairs are inserted into or deleted from the molecule


Gene expression

  • Some mutations involve larger DNA segments

    • Due to change in chromosome structure

    • Wide range of effects as they involve many genes

      • DNA sequences that “jump” into the middle of a gene

      • Known as transposons or transposable genetic elements

      • Most are retrotransposons


Gene expression

Mutations


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