Photosynthesis

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Outline

• Eukaryotic Regulation
• Transcriptional Control
• Posttranscriptional Control
• Translational Control
• Posttranslational Control

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Eukaryotic Regulation

• A variety of mechanisms
• Five primary levels of control
• Nuclear levels
• Chromatin Packing
• Transcriptional Control
• Posttranscriptional Control
• Cytoplasmic levels
• Translational Control
• Posttranslational Control

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Regulation of Gene ExpressionLevels of Control
in Eukaryotes
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Chromatin Structure

• Eukaryotic DNA associated with histone proteins
• Together make up chromatin
• As seen in the interphase nucleus
• Nucleosomes
• DNA wound around balls of eight molecules of
  histone proteins
• Looks like beads on a string
• Each bead a nucleosome
• The levels of chromatin packing determined by
  degree of nucleosome coiling

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Levels of Chromatin Structure
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Chromatin Packing

• Euchromatin
• Loosely coiled DNA
• Transcriptionally active
• Heterochromatin
• Tightly packed DNA
• Transcriptionally inactive
• Barr Bodies
• Females have two X chromosomes, but only one is
  active
• Other is tightly packed along its entire length
• Inactive X chromosome is Barr body

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X-Inactivation in Mammalian Females
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Transcriptional Control

• Transcription controlled by proteins called
  transcription factors
• Bind to enhancer DNA
• Regions of DNA where factors that regulate
  transcription can also bind
• Always present in cell, but most likely have to
  be activated before they will bind to DNA

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Lampbrush Chromosomes
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Initiation of Transcription
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Posttranscriptional Control

• Posttranscriptional control operates on primary
  mRNA transcript
• Given a specific primary transcript
• Excision of introns can vary
• Splicing of exons can vary
• Determines the type of mature transcript that
  leaves the nucleus
• May also control speed of mRNA transport from
  nucleus to cytoplasm
• Will affect the number of transcripts arriving at
  rough ER
• And therefore the amount of gene product realized
  per unit time

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Processing of mRNA Transcripts
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Translational Control

• Translational Control - Determines degree to
  which mRNA is translated into a protein product
• Presence of 5' cap
• Length of poly-A tail on 3' end
• Posttranslational Control - Affects the activity
  of a protein product
• Activation
• Degradation rate

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Review

• Eukaryotic Regulation
• Transcriptional Control
• Posttranscriptional Control
• Translational Control
• Posttranslational Control

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