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BIOB11H3 Study Guide - Midterm Guide: Nucleolus, Nucleoplasm, Coiled Coil

Biological Sciences
Course Code
Dan Riggs
Study Guide

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BIOB11-L8: Nuclear & Chromatin Structure
Anatomy of Nucleus
Nuclear envelope: Double membrane system surrounding the nucleus, continuous with rER
Nuclear pore complex: Basket-like structure regulating the in/out movement of molecules to nucleus
Nuclear pore
Nucleolus: Subnucleus structure where rRNA genes clustered, and assembly of rRNAs
Nucleoplasm: The ‘plasm’ of nucleus
Chromatin fiber: DNA coils with histones to form chromatin fiber
Nuclear matrix: ???
DNA/Protein complex that constitutes chromosomes
*Theres approximately equal amounts of DNA & Proteins
Proteins include Structural Proteins [Histones and Proteins involved in DNA metabolism (e.g. TFIID)]
Nuclear Envelope Structure
- Double membrane, the Nuclear envelope is continuous with the Rough ER
- Inner surface are lined with Lamina Made with Lamins (IF class) Mesh-like network
Gives strength and protection to nuclear envelope
- Lamina also make contacts with heterochromatin (‘silent chromatins’) , stabilizing it.
Nesprin family protein: ???
Nuclear Pore Complex
Made up of 8 subunits, approx. 30 nucleoporin proteins in each subunit
Import: Proteins (enzymes associated w/ DNA replication & transcription) have to move in
Export: RNAs, RNA/Protein complexes have to be exported
How do proteins know to go to the nucleus?
- Small proteins can freely diffuse into the nucleus (~40000 Daltons is the cut-off)
- Larger proteins possess specific signals: NLS
Nuclear Localization Signal (NLS): One to several different regions of a protein that contain short stretches of + charged AAs
Movement of large proteins from cytoplasm to nucleus requires NLS and other proteins
Importins: Soluble heterodimers which bind to NLS-containing proteins
Exportins: Guide Proteins/RNAs from nucleus to cytoplasm by interacting with Nuclear Export Signals
*Both importins & exportins are encoded by gene families
**Ran-GTP: Also carry Importin β using GTP energy Become Ran-GDP in cytoplasm
Chromosome Packaging: The Pasta Analogy
Human cells have DNA >2 meters Must fit into nucleus with 10µm diameter
1st Level Packaging: Interactions of Histones & DNA
Decondensed DNA: Allows access for enzymes of DNA metabolism (Spaghetti) Tangles & Break easily
Condensed DNA: Permits segregation without tangling / breakage (Breadsticks)
Core histones: Very conserved (H2A, H2B, H3, H4) // Linker histone: Much less conserved (H1)
Interaction of Histone proteins w/ DNA
1) Ionic bonds between -ve charged phosphates of DNA & the +ve charged Lys & Arg of histones
2) H bonds between DNA backbone & AAs of histones
3) Non-covalent interactions between histones
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