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Animal Gene expression.docx

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BIOL 112
Karen Smith

Biol 121 225 Freeman Ch. 18, 21 Mar. 3, 10 Genetics 11 – Eukaryotic Gene Expression Differentiation -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 Source -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 1) Chromatin/condensation – if DNA is condensed, RNAP cannot access and occur in eukaryotes? 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 Cancer -uncontrolled cell growth -Caused by -caused by: 1) Defect in cell cycle control 2) Mutation that knocks out key genes -tumour suppression genes -are the brakes on the cell cycle to avoid abnormal growth -proto-oncogenes -genes that encourage cell growth – initiate phases of cell cycle -oncogenes -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 (apoptosis) Development (four processes) 1) Cell division 1) -cells must divide for organism to grow -sometimes, cell death/apoptosis is a normal part of development and is carefully timed and regulated 2) 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) 3) Differentiation -specialized type of cell, to perform a specific function in the multicellular organism Biol 121 225 Freeman Ch. 18, 21
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