The nuclear envelope consists of an inner and outer nuclear membrane separated by the perinuclear space and punctuated by nuclear pore complexes. It encloses the nuclear DNA and separates the nucleus from the cytoplasm. The nuclear lamina, composed of lamin proteins and membrane proteins, lies underneath the inner nuclear membrane and provides mechanical support. Nuclear pore complexes have an octagonal symmetry and allow regulated transport of macromolecules between the nucleus and cytoplasm through import and export signals and adapter proteins.

1. THE NUCLEAR
ENVELOPE,
NUCLEAR LAMINA
& PORE COMPLEX

2. TOPICS TO COVER:
Nuclear envelope:
 Nuclear membranes – inner & outer membranes.
 Nuclear lamina
 Nuclear pore complexes
– structure
– function

3. NUCLEAR ENVELOPE
Nuclear envelope : consists of two nuclear membranes
that envelops the nucleus of an eukaryotic cell, an
underlying nuclear lamina, and nuclear pore
complexes.
 Encloses nuclear DNA.
 Defines the nuclear compartment.
 Separates nucleus and cytoplasmic contents  separate
metabolic compartments.
 Structural framework for nucleus.

4. TOPICS TO COVER:
Nuclear envelope:
 Nuclear membranes – inner & outer membranes.
 Nuclear lamina
 Nuclear pore complexes
– structure
– function

5. NUCLEAR MEMBRANES:
2 lipid bilayer membranes:
•Punctured  nuclear pores  connect the two
membranes.
•Different in protein composition
•Separated by perinuclear space
Inner membrane – associated with nuclear
lamina
Outer membrane – continuous with
endoplasmic reticulum

6. NUCLEAR MEMBRANES:

8. TOPICS TO COVER:
Nuclear envelope:
 Nuclear membranes – inner & outer membranes.
 Nuclear lamina
 Nuclear pore complexes
– structure
– function

9. NUCLEAR LAMINA
•Intermediate filaments & membrane associated proteins
(Lamins & nuclear lamin-associated membrane proteins)
•Lamin types: A, B1, B2, & C
•Mechanical support
•Regulates cellular events

10. TOPICS TO COVER:
Nuclear envelope:
 Nuclear membranes – inner & outer membranes.
 Nuclear lamina
 Nuclear pore complexes
– structure
– function

11. STRUCTURE OF THE NUCLEAR
PORES:
•Large compared to other
proteins.
•Octagonal symmetry.
•Mass approx. 125
megaDaltons in vertebrates.
•Cytoplasmic fibrils (tentacle-
like)
•Nuclear meshwork

12. STRUCTURE OF NUCLEAR
PORE

13. STRUCTURE OF NUCLEAR
PORE

15. FUNCTION OF NUCLEAR
PORE

16. FUNCTION OF THE NUCLEAR PORE
 Passive diffusion of low molecular weight solutes
 Regulated transport of macromolecules larger
than 40 kDa
 Nuclear import signal: NLS
 Nuclear export sequence: NES
 Importins: cytoplasm to nucleoplasm
 Exportins: nucleoplasm to cytoplasm
 GTPase Ran controls interactions of cargo and
karyopherin