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Molecular Genetics: DNA

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Molecular Genetics-summary of transcription ... Molecular Genetics-Roles of RNA. At least 3 types of RNA required for translation of proteins ... – PowerPoint PPT presentation

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Title: Molecular Genetics: DNA


1
Molecular Genetics DNA
  • Four roles for DNA
  • Information storage
  • Replication (reproduction)
  • Day to day instructions to the cell
  • Mutation

2
Molecular Genetics DNA
  • Pro- and eukaryotic genes are organized
    differently.
  • Prokaryotic genes are tightly-packed and
    streamlined.
  • Eukaryotic genes are spread out and hard to
    control, much more complex.

3
The Circular Genome of E. coli
Almost no waste DNA between genes Few repeated
DNA sequences Genes that have to work together
are close to each other Controlled as a unit-
an operon
Genes for lactose metabolism make up an operon
4
Eukaryotic genes and genomes
  • Generic gene for an mRNA reveals important
    features
  • Interrupted genes (introns and exons)
  • Many control regions
  • Much wasted DNA

5
Example-globin
  • Gene families
  • Regulation must be coordinated
  • Much non-coding sequence between genes

6
Example-globin
  • Hereditary globin deficiencies are called
    thalassemia
  • Less susceptible to lethal strains of malaria?
  • Cooleys anemia

7
Molecular Genetics-summary of transcription
  • DNA instructions are put into action by RNA,
    which is directly copied from a DNA molecule
  • (transcription)
  • Produces different types of RNA
  • ribosomal RNA rRNA, messenger RNA mRNA,
    transfer RNA tRNA
  • Some of the RNAs go on to produce protein
  • Others have different jobs

8
Molecular Genetics-summary of transcription
  • Trancription carried out by enzymes called RNA
    polymerases
  • Very large enzymes that are under tight control
    by other proteins

9
Molecular Genetics-RNA processing
  • RNA molecules must be heavily modified after
    transcription
  • This is called RNA processing

10
Molecular Genetics-RNA processing
  • Eukaryotic mRNA processing most complex
  • Involves cutting and splicing of genetic
    information

11
Molecular Genetics-Roles of RNA
  • All RNAs must be processed
  • After processing, some of them are directly
    active as RNA molecules (rRNA, tRNA, regulatory
    RNAs)
  • One type (mRNA) serves as physical carrier of DNA
    information that will be translated into protein

12
Molecular Genetics-Roles of RNA
  • At least 3 types of RNA required for translation
    of proteins
  • rRNA structure and catalytic heart of ribosome
  • tRNA brings amino acids to ribosome-adaptor
  • mRNA carries DNA message to ribosome
  • Regulatory RNAs are often needed as well

13
Molecular Genetics-tRNA
  • Adaptor or interpretor-amino acids and mRNA
  • Anticodon is complementary to an mRNA codon
  • 3 end is covalently attached to an amino acid by
    an enzyme

14
Molecular Genetics-translation
  • Message read one codon at a time
  • tRNAs enter and leave successively
  • Ribosome forms peptide bonds

15
Polyribosome or polysome
16
Gene Expression in Prokaryotes
  • Expression mainly by controlling transcription
  • Constitutive or housekeeping genes expressed
    continually-always on
  • Other genes not produced continually
  • Only on when needed

17
Operon organization
  • Genes that work together are located together
  • They are controlled as a unit
  • Streamlined, efficient, saves resources

18
The genome is organized in units called operons
19
Eukaryotic gene expression
  • Much more complex
  • Many control sequences and proteins for each gene

20
Eukaryotic gene expression-transcription factors
  • Many proteins must be present for gene to be
    active

21
Eukaryotic gene expression-transcription factors
  • All your somatic cells have the same DNA
  • Different tissues have different transcription
    factors-different genes are expressed

22
Endocrine disruptors
  • Environmental pollutants that mimic hormones
  • Interact with transcription factors to activate
    wrong genes
  • Birth defects, cancer?
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