Moving into the nucleus Flashcards
What does sub cellular compartmentalisation allow for?
Complex control mechanisms
What does localisation to membrane-bound compartments do?
Modulates interactions between proteins Depends on molecular signals Increases relative concentrations of species Regulation of the local environment Provides a level of control
Where does gated transport take place?
At pore complexes
What is the difference between transmembrane and vesicular transport?
Transmembrane transport involves direct passage across intact membranes
Vesicular transport does not involve passage across membranes
What does the nucleus separate?
Genetic material from the rest of the cell
Which is the most prominent sub cellular compartment?
The nucleus
What separates the nucleus from the cell?
The nuclear envelope
What is the structure of the nucleus?
Nuclear membrane is a phospholipid bilayer
Outer membrane is continuous with the endoplasmic reticulum
Inner membrane has an underlying meshwork of filaments called the nuclear lamina
Nucleolus
What does the nuclear pore complex enable?
Enables active bi-directional transport of molecules/proteins
What is the molecular weight of a nuclear pore complex?
125 MDa
How more nuclear pore complexes are there in the nucleus?
~3000
At what rate can the nuclear pore complex transport protein?
1000 per minute
What can move through the nuclear pore complex?
Free movement of small molecules
Selective transport of larger proteins
What is a nuclear pore complex made of?
500 subunits of 30 individual proteins called nuclear porins
What is the structure of the nuclear pore complex?
8-fold symmetric structure that rivets the double nuclear membrane together
What are the 4 classes of nucleoporins?
Transmembrane
Core scaffold
Linker
FG
What moves through the nuclear pore complex by passive diffusion?
Small molecules
Metabolites
Ions
What is dependent on energy to travel through the nuclear pore complex?
Proteins mRNA tRNA Ribosomal subunits Viruses
What regulates the export and import of proteins across the nuclear membrane?
A cycle of interactions between:
Protein cargo
Nuclear transport receptors (importins and exportins)
Small GTPase Ran
What are the three phases to export and import through the nuclear pore complex?
Cargo is recognised and bound by nuclear transport receptors
This docks on the pore complex via FG nups and cargo is translocated through the NPC
NTR-cargo dissociated
How are cytosolic proteins directed to the nucleus?
Nuclear localisation sequences
Can be anywhere in the proteins sequence
Artificial tagging of an NLS is sufficient for relocation
What are importins?
Formed of importin a and b that form a heterodimer
Importin a recognises the NLS on cargo protein
Importin b interacts with the pore complex via FG repeats
RanGTP bings importin b and triggers release of the cargo
Importins are recycled back to the cytoplasm
Describe importin b?
19 helical repeat motifs 1-8 bind RanGTP 7-19 interact with importin a 4-8 interact with nucleoporins Importin b forms a superhelical structure that wraps around the IBB domain of importin a
How is directionality controlled?
The RanGTP-GDP gradient
