Chapter 11 and 12 - Nucleus and Control of Gene Expresion

Influence chromatin in 2 ways serve as docking sites

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Unformatted text preview: ne proteins, alter the way in which histones of neighboring nucleosomes interact with one another enzymes (de)acetylate, (de)methylate, and (de)phosphorylate Some proteins bind selectively to modified histones Histone Code formation of heterochromatin o Heterochromatin has many methylated H3 histones, which stabilize the compact nature of the chromatin 8 o o o o o o o Lysine residue at position 9 of the H3 histone in heterochromatin is usually methylated, in euchromatin it remains unmethylated in euchromatin it is often acetylated Removal of acetyl groups from H3 histones is one of the initial steps of conversion of euchromatin to heterochromatin Histone deacetylation is accompanied by H3K9 methylation by histone methyltransferase Methylated H3K9 can then bind proteins containing a chromodomain Interaction of chromodomain protein promote compaction Small RNAs target genome regions to undergo H3K9 methylation and heterochromotinization Chromodomains containing protein = heterochromatic protein 1 Mitotic Chromosomes o o Interphase cell has mainly dispersed chromatin (euchromatin) Chromosomes in mitotic cells are in their most condensed state delivery of package to daughter cell Telomeres o o o o The end of each chromosome is called a telomere and is distinguished by a set of repeated sequences New repeats are added by a telomerase Telomeres are required for the complete replication of the chromosome because they protect the ends from being degraded Telomerase activity is thought o have major effects on cell life Centromeres o o o o Centromeres contain constitutive heterochromatin Centromeric DNA is the site of microtubule attachment during mitosis DNA sequence is not important for centromere structure and function A centromere is marked by a distinct indentation Non genetic inheritance o o Epigenetic inheritance depends on factors other than DNA sequences Parental histones determine the chemical modifications found in newly synthesized histones The Nucleus o o o o o Chromatin fiubers are concentrated at specific domans within the nucleus anchored to cytoskeleton Chromosome ordering is directed by the nuclear envelope proteins In the nucleus, mRNAs are synthesized at discrete sites DNA sequences that participate in a common biological response but reside on different chromosomes interact within the nucleus DNA sequences might influence one another s transcription activity or distant genes may simply share a common poor of transcription proteins Chromosomal Aberrations o A chromosomal aberration is loss or exchange of a segment between different chromosomes 9 o o o o o Chromosomal aberrations have different consequences depending on whether they are in somatic or germ cells Inversions involve breakage of a chromosome and resealing of segment in reverse order particularty damaging in gametes can occur during crossing over in meiosis Translocations are the result of the attachment of all or one piece of one chromosome to another chromosome Deletions result when there is loss of a portion of a chromosome Duplications occur when a portion of a chromosome is repeated 10...
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This document was uploaded on 04/10/2014.

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