Cytology · MU Pleven

Topic 15. Ultrastructural organisation: structure of the nuclear envelope – nuclear pores

Explains the two-membrane structure of the nuclear envelope, including the perinuclear space, the nuclear lamina of intermediate filaments and its role in breakdown and reassembly during mitosis, and nuclear envelopathies. It then describes nuclear pore complexes: their nucleoporin composition, the three rings with eight-fold symmetry, the fibrils and terminal basket, and the central diaphragm. Finally it covers which molecules move in each direction, ribosomal subunit export, and the GTP-driven, GTPase-directed transport.

Inside: 4 sections · 1 labelled picture · 14 flashcards · 3 min

Topic 15 of 59 in the MU Pleven syllabus for Cytology (Medicine, Year 1). The free AceMed note covers it in 4 sections, about 359 words (3 min of reading), with 14 flashcards.

In this note

  1. TOPIC 15. Ultrastructural organisation: structure of the nuclear envelope – nuclear pores
  2. Nuclear envelope
  3. Nuclear pores
  4. function

Nuclear envelope

The nuclear envelope is formed by two membranes.

  • The outer nuclear membrane faces the cytoplasm and is continuous with the RER and the inner nuclear membrane faces the nucleoplasm.
  • The space in between is called the perinuclear space which is continuous with the cisternal space of the endoplasmic reticulum.
  • The inner nuclear membrane is covered by the meshwork of the nuclear lamina which is composed of intermediate filaments called nuclear laminas A, B, C. These nuclear laminas play an important role in the rapid breakdown of the nuclear envelope at the start of mitosis and its reassembly at the end of mitosis.
  • The nuclear envelope forms a selectively permeable barrier between the nucleus and cytoplasm.
  • Nuclear envelopathies are the diseases associated with defects of the nuclear envelope

Nuclear pores

Nuclear pores are what make the nuclear envelope semi permeable.

  • The inner and outer nuclear membranes are joined at nuclear pore complexes.
  • Nuclear pore complexes contain more than 30 proteins (nucleoporins) and span both membranes of the nuclear envelope and regulate the bidirectional transfer of macromolecules between the nucleus and the cytoplasm.
  • Each pore contains 3 rings – (cytoplasmic, luminal and intranuclear ring) with 8 protein subunits arranged in an octahedral central framework at the periphery of the pore. Eight short protein fibrils protrude from the cytoplasmic rings into the cytoplasm. The nuclear ring anchors a basket assembled from 8 thin filaments joined distally by a protein terminal ring.
  • The cylindrical central framework encircles the central pore, which acts as a close-fitting diaphragm.

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