BIOL10004 Chapter Notes - Chapter 4: Cytoskeleton, Chromatin, Plastid
Eukaryotes I – CHAPTER 4
Division of labor in eukaryotic cells
Enormous variety of eukaryotes
Structure of their cells are fundamentally same
Possession of internally, membrane-bounded 'organelles'
Most important - 'nucleus'
oControl center of cell
oCompartment where DNA is stored
Organelles (mitochondria, plastids, vacuoles and endoplasmic reticulum)
Also contains structures not surrounded by membrane, ribosomes and microtubules
Subcellular component carries out specific functions
Organelles and other subcellular components lie in the 'cytosol' an aqueous solution of gel-
like consistency
Cytosol + subcellular components, excluding nucleus - cytoplasm
Cytoplasm + nucleus = protoplasm
Structure and function of nuclei, chromosomes and ribosomes
The nucleus
Dominate feature of eukaryotic cells
Contains most of the cell DNA
Double membrane "Nuclear Envelope"
Contains one or several nucleoli "dark stain regions with high conc. Of RNA and protein +
DNA
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Nuclear envelope double membrane separated by 50nm
Perforated at intervals by "Nuclear Pores"
oChannels that allow movement of certain molecules
oBetween cytoplasm + nucleoplasm
Outer membrane continuous with Endoplasmic Reticulum
Inner membrane is continuous with outer membrane at nuclear pores
Inner and outer have distinct chemical compositions
Nuclear Pores
oNot simple holes
oContains multiple copies of 30 different proteins
oForms 3 octagonal rings
oDelimits size and shape of pore
oDiameter of channel is about 50nm
oPore proteins form meshwork of fibrils
oProjected from wall into channel, cytosol + nucleus
oSmall molecules (5kDa) diffuse quickly
oLarge molecules (eg DNA + RNA) 100-200kDa, actively transported
Proteins imported into nucleus have short sequence of amino acids
o"Nuclear Localization Signal"
Binds directly/indirectly to cytosolic Nuclear import receptors
Import receptors repeatedly bind and detach from mesh-like proteins in channel
Ferries protein into nucleus
Large molecules possess Nuclear Export Signals binds to Nuclear Export Receptors, active
exportation
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Document Summary
Structure of their cells are fundamentally same. Organelles (mitochondria, plastids, vacuoles and endoplasmic reticulum) Also contains structures not surrounded by membrane, ribosomes and microtubules. Organelles and other subcellular components lie in the "cytosol" an aqueous solution of gel- like consistency. Cytosol + subcellular components, excluding nucleus - cytoplasm. Structure and function of nuclei, chromosomes and ribosomes. Contains one or several nucleoli "dark stain regions with high conc. Nuclear envelope double membrane separated by 50nm. Perforated at intervals by "nuclear pores: channels that allow movement of certain molecules o. Inner membrane is continuous with outer membrane at nuclear pores. Inner and outer have distinct chemical compositions. Nuclear pores: not simple holes o o. Forms 3 octagonal rings: delimits size and shape of pore, diameter of channel is about 50nm o o o o. Projected from wall into channel, cytosol + nucleus. Large molecules (eg dna + rna) 100-200kda, actively transported. Proteins imported into nucleus have short sequence of amino acids o.