EUKARYOTIC GENE

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EUKARYOTIC GENE

• BAHAY GÜLLE
• FATIH UNIVERSITY ART SCIENCE FACULTY BIOLOGY
  DEPARTMANT 4TH YEAR STUDENT

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• Eukaryotes have a complex intracellular
  organization with internal membranes, membrane
  bond-organelles, a nucleus and a welled organized
  cytoskeleton.

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• Eukaryotic cells have several linear chromosomes
  in their nuclei . In each of the chromosomes
  there is a very long DNA molecule packaged by
  histones and other proteins.

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• The number and DNA content of chromosomes are
  different among different species.
• Human genome 3x109 nts
• Onion 15x109 nts
• Lily 90x109 nts

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Prokaryotic vs. Eukaryotic Genes

• Prokaryotes
• small genomes
• high gene density
• no introns (or splicing)
• no RNA processing
• similar promoters
• overlapping genes

• Eukaryotes
• large genomes
• low gene density
• introns (splicing)
• RNA processing
• heterogeneous promoters
• polyadenylation
•  

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Genome Size

• Eukaryotic genomes may be so large, in part,
  because most eukaryotic genes in higher
  eukaryotic organisms are interrupted by introns.

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• The main proportion of DNA in the genomes are
  non-coding sequences, thus gen density is low in
  eukaryotic genomes. (The total number of gene in
  human is estimated to be 30,000-40,000

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• Most eukaryotic genes are DNA sequences that are
  never translated into polypeptides. These
  noncoding regions, called introns, alternate with
  regions called exons that are expressed in the
  polypeptide sequence.

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Protein-coding genes have

• exons whose sequence encodes the polypeptide
• introns that will be removed from the mRNA before
  it is translated
• a transcription start site
• a promoter
• -the basal or core promoter located within about
  40 bp of the start site
• -an "upstream" promoter, which may extend over
  as many as 200 bp farther upstream

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• The transcription start is usually associated
  with an AT rich DNA sequence about 25 bp away
  from the initiation - the TATA box
• Upstream anywhere from 50 to 100 bases from the
  TATA box is another sequence associated with
  transcription initiation - the CAAT box. This
  sequence may not be necessary in all genes.

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Eukaryotic Gene Control Eukaryotic control sites
include promoter consensus sequences similar to
those in bacteria.
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• In eukaryotes the splicing process of a
  pre-mRNA can lead to different ripe mRNA
  molecules and therefore to different proteins.
  This phenomenon is called alternative splicing.

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• When the pre-mRNA has been transcribed from the
  DNA, it includes several introns and exons. But
  what is an intron and what is an exon is not
  decided yet. This decision is made during the
  splicing process.

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For eukaryotes it was a very important step
towards higher efficiency.

• The information can be stored much more
  economically.
• New proteins can evolve much faster than in
  prokaryotes.
• Therefore the adaptation to new environments can
  be much faster - with fewer generations - than in
  prokaryotes.

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THANKS.....