BIOL 1090 Study Guide - Ribosomal Rna, 18S Ribosomal Rna, 5.8S Ribosomal Rna

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27 Apr 2012
The Nucleus
A. Function
- storage, replication, and repair of genetic material
- expression of genetic material
o transcription (mRNA, tRNA, rRNA)
o splicing
- ribosome biosynthesis
o there are no active ribosomes in the nucleus, only partially assembled ones
- segregation of transcription and translation large tenet of eukaryotic cells
o major separation between cytoplasmic and nuclear activity
o translation occurs in the cytoplasm, transcription in the nucleus
The Nuclear Envelope
- nuclear membrane, nuclear pores, nuclear lamina
A. Structure
- two parallel phospholipid bi-layers separated by 10-50nm
o different than other membranes we’ve discussed
- outer membrane binds ribosomes
o continuous with rough ER
o intermembrane space continuous with ER lumen
- inner membrane bears integral proteins, which connect to nuclear lamina
- supported by nuclear lamina
- very solid structure; hard to disrupt; cells can rupture and NE will remain intact
B. Function
o separates nuclear content from cytoplasm
segregates transcription and translation
o selective barrier
allows limited movement of molecules between nucleus and
cytoplasm using channel proteins
The Nuclear Lamina
C. Structure
- thin meshwork of filamentous proteins next to the nucleoplasmic leaflet of the
inner nuclear membrane
o lamins (class V IFs)
- bound to inner membrane of NE by integral membrane proteins
- provides structural support for NE
- associates with DNA; provides attachment sites for chromatin
o creates specialized regions of activity, allowing relevant parts of DNA to
be accessed by transcription “machinery”
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