Regulation of Gene Expression

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Regulation of Gene Expression
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You Must Know

• The functions of the three parts of an operon.
• The role of repressor genes in operons.
• The impact of DNA methylation and histone
  acetylation on gene expression.
• The role of oncogenes, proto-oncogenes, and tumor
  suppressor genes in cancer.

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Bacteria respond to environmental change by
regulating Transcription.

• Genes are clustered into units called operons.
• 3 parts of an operon
• Operator- controls the access of RNA polymerase
  to the genes.
• Promoter-where the RNA polymerase attaches.
• Genes- The entire stretch of DNA required for al
  the enzymes produced by the operon.

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General structure of an OPERON
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Regulatory Genes

• Produce repressor proteins that may bind to the
  operator site.
• When they occupy the operator site, RNA
  polymerase is blocked from the genes of the
  operon.
• This means the operon is off.

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Repressible Operon

• Is normally on but can be inhibited.
• Is Anabolic, building an organic molecule.
• The repressor protein produced by the regulatory
  gene is inactive.
• If the organic molecule that is produced is
  provided to the cell, the molecule can act as a
  corepressor and bind to the repressor protein,
  activating it.

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Inducible Operon

• Normally off, but can be operated.
• Normally catabolic, breaking down food molecules
  for energy.
• To turn the inducible operon on, an inducer binds
  to and inactivates the repressor protein.
• Now RNA polymerase can access the genes of the
  operon.

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Regulation of Genes

• The expression of Eukaryotic genes can be turned
  off and on at any point along the path to
  becoming a protein.
• Different cell types are due to differential gene
  expression, the expression of different genes by
  cells with the same genome.

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Packaging of DNA

• A nucleosome is a packaging unit of DNA.
• Consists of DNA bound ot small proteins called
  histones.
• The more tightly bound DNA is to its histones,
  the less accessible it is for transcription.
• This relationship is governed by 2 chemical
  reactions.
• DNA methylation- the addition of Methyl groups to
  DNA
• Causes DNA to become more tightly packaged, thus
  reducing gene expression.
• Histone acetylation- acetyl groups are added to
  amino acids of histone proteins, making the
  chromatin less tightly packaged, encouraging
  transcription.

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Recap

• Methylation- occurs on DNA reduces gene
  expression
• Acetylation- occurs on histones increases gene
  expression

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Other factors of Gene expression

• Transcription initiation is another important
  control point in gene expression.
• The control of gene expression may also occur
  prior to translation and just after translation,
  where proteins are processed.

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Connection to real life

• Cardiovascular disease
• Gene expression provides valuable, tissue and
  cell-specific information about the molecular
  mechanisms involved in disease processes,
  allowing a clinician to, for example, evaluate
  cardiovascular disease state, activity, and/or
  progression at a point in time.

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Links

• http//web.mit.edu/bioedgroup/animations.htm

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A program of differential gene expression leads
to the different cell types in a Multicellular
organism.

• Zygote undergoes transformation through three
  interrelated processes.
• Cell division
• Cell differentiation- cells specialize
• Morphogenesis- organization of cells into tissues
  and organs.

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What controls differentiation Morphogenesis?

• Cytoplasmic Determinants
• Maternal substances in the egg that influence the
  course of the early development.
• They are unevenly distributed in the early cells
  of the embryo and result in different effects.
• Cell-cell signals
• Results from molecules, such as growth factors
  produced by one cell influencing neighboring
  cells, a process called induction which causes
  cells to differentiate.

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• Determination
• Series of events that lead to observable
  differentiation of a cell.
• Differentiation is caused by cell-cell signals
  and is irreversible.
• Pattern Formation
• Sets up the body plan and is a result of
  cytoplasmic determinants and inductive signals.
• Determines head and tail, left and right, back
  and front.
• Uneven distribution of morphogens plays a role in
  establishing these axes.
• Stem Cell Animation

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Cancer Results from genetic changes that affect
cell cycle control.

• Oncogenes- are cancer-causing genes.
• Proto-oncogenes- genes that code for proteins
  that are responsible for normal cell growth.
• Become oncogenes when a mutation occurs that
  causes an increase in the product of the
  proto-oncogene,
• Or
• an increase in the activity of each protein
  molecule produced by the gene.

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• Cancer can be caused by a mutation in a gene
  whose products normally inhibit cell division.
• These genes are called tumor-suppressor genes.
• Cancer development is based on the idea that
  cancer results from the accumulation of mutations
  that occur throughout life.
• The longer we live, the more mutations that are
  accumulated and the more likely that cancer might
  develop.

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Activities

• This weeks CAR
• What does Stem cell Research Mean to you?
• Different types of Stem Cells?
• How are they cultured in the lab?
• What are some issues in Stem cell research?
• What are some issues that you have?