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How many membranes make up the nuclear envelope?

2-- the outer and inner envelope


What separates the two nuclear membranes?

The perinuclear space. It is 20 nm in width


What is the difference between the outer and inner membranes of the nuclear envelope?

The outer membrane has ribs attached to it and is contiguous w/ the rough and smooth RER.

The inner membrane is associated w/ fibrous lamina-- called the nuclear lamina


What are nuclear pores?

They join the outer/inner nuclear membrane at numerous sites and they are about 80 nm in diameter


Where is the nuclear lamina? What makes it up? Name 3 functions of the nuclear lamina.

It is on the inside of the nucleus-- associated w/ inner nuclear membrane and pore complexes. It has 50 nm thick layer of fibrous proteins called "nuclear lamins"

(1) Structural stability for the nucleus
(2) Anchors chromatin and nuclear pore complexes
(3) Regulates assembly/disassembly of the nuclear envelop during mitosis


What regulates assembly/diassamly of the nuclear envelope during mitosis?

The nuclear lamina


What causes Progeria? What kind of disorder is this?

It is caused by a point mutation that creates an unusable form of Lamin A. As a result, the nuclear lamina cannot be formed properly. Children w/ this disorder age very quickly and usually only live until teen years.


What causes restrictive dermopathy? Explain mechanism

It is an autosomal recessive disorder. A gene that is normally responsible for the cleavage of pre-lamia into mature nuclear lamin is lost. As a result, the skin cannot grow w/ the fetus. The fetus essentially suffocates in its own skin


Nuclear pore complexes

8 subunits that form annuli. connect the inner/outer membranes. Gateway b/t the nucleus and city.


What makes up nuclear pore complexes?

Intermediate filaments


What is the nuclear matrix made up of? What occurs there? How is it detected?

It is made up of fibrillar proteins. RNA processing occurs here. It is detected after removing DNA/RNA -- using nucleases and extraction


How many nucleoli within each nucleus?

One or many


What is produced in the nucleolus?

Ribosomes. There are clusters of ribosomal RNA in what is called the nucleolar organizer region of the chromosome


Where are small ribonucleoprotein complexes formed?

In the nucleoli-- these are necessary to begin to assemble ribosomes


Where does final ribosomal assembly take place?

In the cytoplasm


What is chromatin made up of?

It is highly condensed nuclear DNA complexed w/ proteins called histone and non histone proteins


What is the difference between heterochromatin and euchromatin? How are they similar?

Differences-- heterochromatin is tightly wound, therefore it is not undergoing transcription. Euchromatin is more diffuse and representative of active gene transcription.
Similarities: Both are forms of nuclear chromatin


What kind of substances are able to diffuse through the nuclear membrane to enter/ exit the nucleus/

Ions and small metabolites. Small proteins less than 30kDa could theoretically move through- but they mainly exhibit regulated nuclear transport.



A genetic disease of highly accelerated aging. Die in teens from atherosclerosis. Less than 300 cases worldwide


How is restrictive dermopathy caused?

It is an autosomal recessive rare and lethal disease. The gene that cleaves prelamin into mature nuclear lamina is lost-- this results in no mature lamina specific to the skin, the skin cannot grow and essentially the fetus is suffocated


Are nuclear lamins cell type specific?

No -- they are the only intermediate filaments that are not cell type specific


What do lamins connect in the cell?

They connect chromatin to the nuclear membrane


When are lamins in the dephosphorylated state?

During interphase, when the nuclear envelope is intact


When are lamins phosphorylated?

They are phosphorylated by a kinase early in mitosis. This causes the nuclear membrane connection to break and begins pronuclear membrane disassembly.


When do lamins return to a dephosphorylated state? How does this occur?

Late in mitosis; A phosphatase removes the P and permits the membrane to reassemble.


Which experiment was conducted to prove that nuclear transport occurs via nuclear pores?

Nuclear proteins were labeled w/ tiny gold particles in the lab and microinjected into the cytoplasm of cultured rat cells. The gold particles were tightly clustered in the regions where the inner and outer nuclear membranes came together i.e., the pores


Cargo smaller than ____ kDa can enter the nucleus via diffusion through nuclear pores, but larger cargo must be ______ transported through nuclear pores

5-10 kDa; "Actively"


What is required for cargo import?



How is cargo escorted to the nuclear pore?

Chaperone proteins --- e.g. importing can bind to the NLS on cargo and escort to the nuclear pore


How are proteins and ribonucleoprotein complexes exported?

They contain NES that are recognized by exporting-- the exporting recognize a specific 5' Gppp site on the nuclear pore and bind to it


What does exportin -1 transport? Why is this significant in cancer?

They have a selective set of cargos-- they specialize in exporting tumor suppressors, apoptosis inducers, and anti-proliferative molecules that exert their normal biological activities via binding to DNA. Cancer cells over-express exportin 1. This is a target


Describe how proteins and RNPs are transported out of the nucleus?

“Receptors exist on the nucleoplasmic face of the pore complex and regulate the exit of proteins and RNPs from the nucleus.
Analogous to nuclear import, nuclear export signals (NES) exist on proteins or ribonucleoprotein complexes (RNPs) destined for export.  The NES binds to receptors on the nuclear pore complex and subsequently exported.
Note that in the case proteins or RNPs destined for export, the nuclear pore complex specifically detects a special methylated 5’-pppG cap.”

Excerpt From: Dr. John Castellot. “2017-2018 M21 Cell Biology Syllabus.” iBooks.


Energy requirements for nuclear import/export?

ATP is not required for a ligand to bind to the nuclear pore complex, but ATP is required for the actual translocation of a molecule across the nuclear membrane.


Which disease is characterized by aberrant nuclear protein import?

Huntington's Disease


Describe the brain cell nuclei of patients w/ huntingtons

Brain cell nuclei show high accumulations of huntingtin which normally resides in the cytoplasm


Mutant huntingtin protein vs normal protein

“The mutant huntingtin protein appears to have acquired an NLS not present in the wild-type protein. Because the triad repeats that characterize the mutant huntingtin protein are not themselves an NLS, it is likely that the three-dimensional conformation of the mutant protein confers upon it the ability to be transported into the nucleus.

Excerpt From: Dr. John Castellot. “2017-2018 M21 Cell Biology Syllabus.” iBooks.


The severity of huntingtons is correlated w/ the amount of ____ whereas the age of onset is correlated w/ _______-

Huntingtin ; number of trinucleotide repeats