Transcript Regulation of Gene Expression

Regulation of Gene
Expression
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.
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.
General structure of an OPERON
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.
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.
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.
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.
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.
Recap
• Methylation- occurs on DNA & reduces
gene expression
• Acetylation- occurs on histones &
increases gene expression
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.
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.
Links
• http://web.mit.edu/bioedgroup/animations.
htm
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.
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.
– 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
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 protooncogene,
Or
– an increase in the activity of each protein
molecule produced by the gene.
• 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.
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?