Biol 121- 2010.03.03- Genetics- Eukaryotic Gene Expression (Ch. 18, 21).docx

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22 Apr 2012

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Biol 121 225
Freeman Ch. 18, 21 Mar. 3, 10
Genetics 11 Eukaryotic Gene Expression
-is the process by which cells specialize in function
-for example, a cell can become a neuron (nerve cell), a smooth muscle cell,
or a blood cell (WBC or RBC)
Stem cells
-stem cells are cells that have yet to differentiate
-they are able to become any type of cell
-they can be found in bone marrow in adults
-they can also be found in embryos (embryonic stem cells)
Where can control of gene expression
occur in eukaryotes?
1) Chromatin/condensation if DNA is condensed, RNAP cannot access and
therefore transcription cannot occur
2) Transcription where most control occurs with regulatory proteins
3) Alternate splicing a process by which not only introns are removed but
also selected exons during RNA spicing this way, many different mRNAs
may be translated into different proteins therefore, one gene can code for
multiple proteins
-in humans >80% genes are alternatively spliced
-Caused by
-tumour suppression genes
-uncontrolled cell growth
-caused by:
1) Defect in cell cycle control
2) Mutation that knocks out key genes
-are the brakes on the cell cycle to avoid abnormal growth
-genes that encourage cell growth initiate phases of cell cycle
-mutation causes protooncogene to change into encogene
-oncogenes stimulate uncontrolled division cancer
Example of tumour suppression: p53
-p53 codes for regulatory transcription factor protein p53
-mutations in p53 which produces non-functional proteins are found in over
half of all human cancers
How does normal p53 work? (4)
1) DNA damage.
2) p53 protein increases (transcription of p53)
3) p53 binds to DNA (not in same region that is damaged)
4) Transcription of genes that arrest cell cycle or lead to cell death
Development (four processes)
1) Cell division
-cells must divide for organism to grow
-sometimes, cell death/apoptosis is a normal part of development and is
carefully timed and regulated
2) Cell movement and expansion
-many animal cells must move for normal development
-gastrulation: cells in different parts of a mass of cells rearranged themselves
into three distinctive types of embryonic tissues, which then give rise to the
skin, gut , etc
-if migrating cells go to wrong place, embryo likely to be deformed/die
3) Differentiation
-specialized type of cell, to perform a specific function in the multicellular
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