Bio Notes - Biology 101 - Desaix

Bio Notes - Biology 101 - Desaix - 1 March 2007 Chapter 14...

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1 March 2007 Chapter 14: Control of Gene Expression I. Overview a. Does a cell in your ear have a gene for making liver enzymes? Yes! They’re just not turned on. (They’re not being transcribed, so RNA isn’t being made.) b. On top of structural and functional proteins in the cell, there are signal proteins that control gene expression. II. Transcripts are edited a. Process is different in prokaryotes and eukaryotes b. In eukaryote cells, mRNA has a cap and a poly-A tail added (modification of “pre-mRNA” prior to its leaving nucleus for cytoplasm) c. Diagram: portion of mRNA is removed prior to expulsion from nucleus i. Parts that are removed: introns ii. Parts that remain to be expressed: exons iii. Diagram: red chunks remain to be expressed (final product: mature mRNA transcript , or edited mRNA); in numbered yellow, purple, and red diagram, the yellow represents introns d. Diagram: note chromatin changes (?) and mRNA degradation; it is possible for a primary RNA transcript to be put together two ways ( alternate splicing ) III. Chromosomal rearrangements also result in phenotype changes (Test 2) a. Happens a lot during crossing over (unequal swapping leads to one chromosome getting too many genes and the other, too few) b. Diagram: chromosomal alterations i. Deletion: often, a, b, c, d, and e will work together; deletion of “c and d” will sometimes be favorable (elimination of detrimental genes), but most often is lethal ii. Duplication: not such a big problem because it could potentially provide raw material for evolution of new proteins as part of a family of related proteins (?); could interfere with gene function if duplication occurs within a gene iii. Inversion: can disrupt operons ; results in loss of control of gene expression iv. Translocation: between non-homologous chromosomes (often seen in karyotypes for cancer) c. Diagram: unequal crossing over duplication and deletion IV. Differences in genes and chromosomes = information about species relatedness a. Diagram: humans and chimpanzees have over 98% of the same genes, BUT the chromosomes are different (we have one that looks like two of theirs fused) V. Control of gene expression: prokaryotes (remember gene controls are different in prokaryotes and eukaryotes) a. Operons : sequence of genes operating together
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b. Lac operon : related to lac tose *Be able to tell this “story” i. Diagram: lactose-utilization genes (genes that make an enzyme that breaks down lactose); only needed if lactose is present; in the diagram, the lac operon is turned off (it’s not transcribing mRNA) – RNA polymerase is not working; it can’t attach because a repressor (just know it’s a protein) has attached to the DNA upstream (this protein has been translated even further upstream) ii. Diagram: lac operon turned on; the repressor is inactivated by the presence of lactose in that the repressor’s shape is changed so it can no longer attach to the DNA lac operon is turned on VI. Diagram: pipeline
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Bio Notes - Biology 101 - Desaix - 1 March 2007 Chapter 14...

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