Gene Regulation

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Gene Regulation
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Gene Regulation

• Selective Gene Expression
• Cell Differentiation
• Why Regulate?
• Respond to chemical environment
• Respond to physical environment
• Respond to hormones

• Gene Regulatory Proteins
• Turn Genes on and off.
• Directly bond to the DNA.

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Prokaryotic Gene Regulation

• Operon
• Functional gene/regulator unit
• Promotersite of RNA polymerase binding.
• Operatorsite of repressor binding.
• Structural genescode for actual proteins/enzymes

• Regulatory Genescode for repressor proteins.
• Repressor ProteinsBind to operator and turn
  genes on and off.

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Operons

• Inducible operons
• Usually turned off.
• Repressors are normally bound to the operator.
• Used to conserve resources.
• The inducer binds to the repressor and causes it
  to unbind from the operator, thus turning on the
  gene.

• Example lac operon
• Manufactures lactase.

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Operons

• Repressible Operons
• Usually turned on.
• Example trp operon.
• Manufactures tryptophan.
• Corepressortryptophanbinds to the repressor and
  causes the operon to

• Switch itself off.

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Eukaryotic Gene Regulatory Mechanisms

• Exonsexpressed DNA sequences.
• IntronsDNA sequences that are never transcribed.
  Found only in Eukaryotes.
• May play a role in creating variability.

• Levels of control of gene expression
• Transcriptional level control
• Processing level control
• Translational level control

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Transcriptional Level Control

• Gene Regulatory proteins
• Formation of large loops of DNA.
• Hormones
• Testosterone binds to a receptor, this complex
  then binds to the DNA and acts as a gene
  regulatory protein.

• Androgen insensitivity
• Chromosomal puffs
• Ecdysone
• Polytene chromosomes

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RNA Processing Level

• Primary transcript
• Processing
• Introns must be removed.
• Ribozymes
• splicing

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Translational Level

• Proteins may mask mRNAs and prevent them from
  being translated.
• mRNAs may accumulate in dormant cells like ova.
  Once activated these are rapidly translated.

• Cells can also control the life spans of mRNA.