Molecular Cell Biology the nuclear envelop and membrane and pores

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