Introduction, Nucelus Struct and Funct

Question 1

Nuclear Envelope: general structure

Answer 1

two membranes, inner and outer
seperated by perinuclear space, 20nm
morphologically and biochemically distinct
membranes joined at nuclear pores

Question 2

Outer membrane of nuclear envelope

Answer 2

has ribosomes attached

continuous with sER and rER

Question 3

Inner Membrane

Answer 3

Associated with the fibrous lamina called nuclear lamina

Question 4

Nuclear Lamina

Answer 4

inside of the nucleus associated with inner mem and pores

made up of 50nm thick lamins

Question 5

functions of nuclear lamin (3)

Answer 5

gives nucleus structure/stability
anchors chromatin and nuclear pore complexes
regulates disassembly/reassembly of nuc env during mitosis

Question 6

Progeria:
cause and effect
general prognosis

Answer 6

caused by a point mutation
creates an unusable form of the protein Lamin A therefor the nuclear lamina cannot be formed
age quickly and only live into their teens

Question 7

Restrictive Dermopathy:
cause
gene effected
effect

Answer 7

autosomal recessive disorder
loss of gene that is normally resp for the ceavage of a pre-lamin into a mature nuclear lamin
without the lamin, the skin does not grow with the fetus and suffocates in own skin

Question 8

Nuclear Pore Complexes:
protein structure
function

Answer 8

Composed of intermediate fillaments - these are the only intermediate filaments that are not cell specific
8 subunits that form annuli (rings)
connect inner and outer nuclear mem
gateway between the cytoplasm and the inside of the nucleus

Question 9

Nuclear Matrix:
composition
purpose
detection

Answer 9

complex of fibrillar proteins, present in most mammalian nuclei
site of RNA processing
detected only after removal of DNa and RNA (nucleasess and salt extraction)

Question 10

Nucleolus:
abundance
purpose
composition

Answer 10

may be one or many within each nucleus
ribosome production site
composed of large loops of DNA from several chromosomes
contains clusters of ribosomal RNA genes in the nuclear organizer region of chromosome
contain many RNA binding proteins that form small ribonucleoprotein complexes needed to make ribosomes

Question 11

Nuclear Pore Complexes:
protein structure
function

Answer 11

Composed of intermediate fillaments - these are the only intermediate filaments that are not cell specific
8 subunits that form annuli (rings)
connect inner and outer nuclear mem
gateway between the cytoplasm and the inside of the nucleus

Question 12

Nuclear Matrix:
composition
purpose
detection

Answer 12

complex of fibrillar proteins, present in most mammalian nuclei
site of RNA processing
detected only after removal of DNa and RNA (nucleasess and salt extraction)

Question 13

Nucleolus:
abundance
purpose
composition

Answer 13

may be one or many within each nucleus
ribosome production site
composed of large loops of DNA from several chromosomes
contains clusters of ribosomal RNA genes in the nuclear organizer region of chromosome
contain many RNA binding proteins

Question 14

Signifigance of RNA binding proteins in nucleolus

Answer 14

form many of the small ribonucleocomplexes which are necessary to assemble a ribosome

Question 15

Ribonucleoprotein complexes

Answer 15

formed in the nucleolus then transported into the cytoplasm for assembly of the final ribosome. This prevents a functional ribosome from being exposed to mRNA in the nucleus

Question 16

Chromatin

Answer 16

highly condensed nuclear DNA complexed with proteins called histones and non-histone proteins

Question 17

When a cell is in interphase, nuclear chromatin can be found in 2 states: names of description of states

Answer 17

Heterochromatin - tightly wound and transcriptionaly inactive

Euchromatin - more diffuse and representative of active gene transcription

Question 18

Transport of ions, small metabolites, and small proteins in ad out of the nucleus

Answer 18

small metabolites and ions use simple diffusion

small proteins less than 30kD sould move via simple diffusion in theory but still move via regulated transport

Question 19

Transport of large metabolites and proteins in and out of nucleus

Answer 19

if they are larger than 5-10kD they need to go through a pore
mediated by active transport

Question 20

Transport out of the nucleus:
detecting molecules
receptors

Answer 20

• nuclear export signals NES exist on proteins or ribonucleoprotein RNP complexesdestined for export. these bind to receptors on nuclear side of pore. The pore specifically detects a special methylated 5’-pppG cap.
• exportin is involved in the transportation process

Question 21

Transport into the cell:
Detecting molecules
movement of molecule
pore receptors

Answer 21

• cytoplasmic side of pore has filaments that detect nuclear localization signals (NLS)
• NLS will bind chaperon proteins called importins and this NLS-importin complex binds to a receptor on the pore allowing transport to occur
• Many pore receptors, not a unique receptor for each nucleus destined protein, rather several classes or receptors exist

Question 22

Note on NLS’s

Answer 22

not a single consensus sequence

tend to conatin high proportions of basic amino acids

Question 23

Transport out of the nucleus:
detecting molecules
receptors

Answer 23

-nuclear export signals NES exist on proteins or ribonucleoprotein RNP complexesdestined for export. these bind to receptors on nuclear side of pore. The pore specifically detects a special methylated 5’-pppG cap.

Question 24

Energy us of nuclear transport

Answer 24

ATP is not required for a ligand to bind a nuclear pore complex
However, ATP is required for the actual translocation of a molecule accross the pore

Question 25

Huntingtons Disease:
cause
severity
onset

Answer 25

• accumulation of the protein, huntingtin, in the nuslei of brain cells. disturbs nuclear function
• this protein is typically found in the cytoplasm
• protein appears to have aquired an NLS but repeats found in the mutant are not a recognized NLS. Its thought that the shape of the mutant allows it to gain access to the nucleus
• severity is proportional amount of huntingtin protein in the nucleus
• age of onset is correlated with the number of trinucleotide repeats added to the protein

Question 26

Chaperon proteins and cancer

-exportin 1

Answer 26

Exportin 1 is a class of exportin that specializes in the export of inhibitors of cell division (tumor suppressors, transcription factors, apoptosis inducers…)

• most cancer cells have elevated levels of exportin 1 which removes these cell div inhib’s from the nucleus where they typically operate - promoting cell growth/div
• small molecule inhibitors of exportin 1 have been manufactured and are now in phase 2 clinical trials

Question 27

During interphase, in what form does the DNa of a cell exist?

Answer 27

as chromatin in either the euchromatin state (actively transcribed) or the heterochromatin state (densely wound)

Question 28

Lamins and their role in the cell cycle:
intephase
beginning the cycle
late in mitosis

Answer 28

• interphase: lamins are in an unphosphorylated state
• early: lamins are phosphorylated by a kinase causing the lamin-nuclear membrane connection to break, thus beginning the dissassembly of the membrane
• late: phoshotases returns the lamins to the unphosphorylated state, allowing nuclear membrane reassmbly to occur