How are macromolecules transported across the nuclear envelope? Describe the structure that
regulates nuclear membrane permeability.
Solution
The transportation of molecules in and out of the nucleus is controlled by the nuclear pore
complex(NPC). Small molecules move through the nuclear membrane with ease but for
macromolecules like proteins, RNA etc, they require an association with transportation factors
like importins, karyopherins and exportins.
Proteins that need to be carried into the nucleus have nuclear localization signals (NLS) which
bind to the importins. NLS is a sequence of Amino acids which act as a tag. They are mostly
hydrophilic but hydrophobic sequences have also been documented.
Nuclear Import:
Importins bind to the macromolecule to be transported in the cytoplasm itself. The complex then
interacts with the NPC and passes through the channel. Once inside the nucleus, it interacts with
Ran-GTP and the importin dissociates from the macromolecule it was carrying. Then the
importin-Ran-GTP complex is transported to the cytoplasm where it is separated from importin
by the Ran Binding Protein (RanBP). After being separated from importin, GTPase activating
protein(GAP) binds with Ran-GTP and induces hydrolysis of GTP to GDP. The Ran-GDP
produced binds with the nuclear transport factor(NUTF2) and then returns to the nucleoplasm.
Inside the nucleus, Ran-GDP interacts with guanine nucleotide exchange factor(GEF) which
replaces GDP with GTP and Ran-GTP is born again to repeat the cycle.
Nuclear Export:
In the nucleoplasm, exportin binds the macromolecule to be transported outside the nucleus and
Ran-GTP. The complex diffuses through the pore to the cytoplasm where it dissociates. Ran-
GTP binds to GAP and hydrolysis resulting in Ran-GDP. Ran-GDP is returned to the nucleus
where it exchanges its ligand for GTP.
Nuclear Pore:
The nuclear pore complex is made of proteins called nucleoporins. Around 50% of nucleoporins
contains solenoid protein domains (alpha or beta-propeller fold) and the rest might have both as
separate structural domains. Each NPS has about 456 individual protein molecules with 30
distinct nucleoproteins. These are highly flexible proteins that lack an ordered secondary
structure..
How are macromolecules transported across the nuclear envelope Desc.pdf
1. How are macromolecules transported across the nuclear envelope? Describe the structure that
regulates nuclear membrane permeability.
Solution
The transportation of molecules in and out of the nucleus is controlled by the nuclear pore
complex(NPC). Small molecules move through the nuclear membrane with ease but for
macromolecules like proteins, RNA etc, they require an association with transportation factors
like importins, karyopherins and exportins.
Proteins that need to be carried into the nucleus have nuclear localization signals (NLS) which
bind to the importins. NLS is a sequence of Amino acids which act as a tag. They are mostly
hydrophilic but hydrophobic sequences have also been documented.
Nuclear Import:
Importins bind to the macromolecule to be transported in the cytoplasm itself. The complex then
interacts with the NPC and passes through the channel. Once inside the nucleus, it interacts with
Ran-GTP and the importin dissociates from the macromolecule it was carrying. Then the
importin-Ran-GTP complex is transported to the cytoplasm where it is separated from importin
by the Ran Binding Protein (RanBP). After being separated from importin, GTPase activating
protein(GAP) binds with Ran-GTP and induces hydrolysis of GTP to GDP. The Ran-GDP
produced binds with the nuclear transport factor(NUTF2) and then returns to the nucleoplasm.
Inside the nucleus, Ran-GDP interacts with guanine nucleotide exchange factor(GEF) which
replaces GDP with GTP and Ran-GTP is born again to repeat the cycle.
Nuclear Export:
In the nucleoplasm, exportin binds the macromolecule to be transported outside the nucleus and
Ran-GTP. The complex diffuses through the pore to the cytoplasm where it dissociates. Ran-
GTP binds to GAP and hydrolysis resulting in Ran-GDP. Ran-GDP is returned to the nucleus
where it exchanges its ligand for GTP.
Nuclear Pore:
The nuclear pore complex is made of proteins called nucleoporins. Around 50% of nucleoporins
contains solenoid protein domains (alpha or beta-propeller fold) and the rest might have both as
separate structural domains. Each NPS has about 456 individual protein molecules with 30
distinct nucleoproteins. These are highly flexible proteins that lack an ordered secondary
structure.
