BCH3021 Lecture Notes - Lecture 11: Nuclear Pore, Nuclear Membrane, Digitonin
Lecture 11 – The Nucleus: Structure and Function
• In animal and plant cell and fungus/yeast
• Evolutionary origin of mitochondria
o Cell engulfed prokaryotic nuclei → mitochondria
• Evolutionary origin of eukaryotic nucleus
o Invagination of plasma membrane containing ribosome → nucleus
Nuclear Structure
• Compartmentalisation of processes in the
eukaryotic cell
o Nucleus keeps DNA away from rest of
cell: compartmentalisation
o Compartmentalisation of nuclear and
cytoplasmic processes through nuclear
envelope (e.g. transcription, RNA
splicing)
o Unlike prokaryotic cell: has no
compartmentalisation
• Nuclear envelope (NE)
o Double membrane structure: inner
and outer membrane
o Barrier between nucleus and
cytoplasm
o A double double lipid bilayer
▪ Contiguous with ER
▪ Shares membrane
phospholipid composition (lack of cholesterol)
▪ Cholesterol targeting detergents (e.g. digitonin) can be used to
permeabilise plasma membrane selectively and leave NE intact
o The inner leaflet is lined by nuclear lamina (skeletal structure) – the
NE breaks down during mitosis
▪ Gives it nucleus solidity structure
o NE is a barrier between nucleus and cytoplasm
▪ Compartmentalises function (separates transcription (nucleus)
and translation (cytoplasm)
▪ Controls passage between the two → occurs through nuclear
pore complexes
• Nuclear pore complex (NPCs)
o Transit path for molecules into and out of the nucleus
o Embedded in nuclear envelop
o 125 x 106 D, spans inner and outer membranes of NE: octagonal
symmetry (8 fibrils)
o Has a pore or molecular sieve function (pore size: 90˚A)
o Made up of 40 different proteins (nucleoporins – nups)
o Protinatous structure
• Nucleoporins (nups)
o Building blocks of nuclear pores – multiple copies
o Different nups are localised to particular sites within NPC
▪ E.g. Gp210 (glycoprotein:MW) and POM121 – integral
membrane components that anchor the NPC in the NE
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