Cell Bio 406 Lecture 6
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Cell Bio 406 Lecture 6
Cellular Biology 406
nuclear structure and transport
What contains most of cell's DNA?
What surrounds the nucleus?
double membrane known as the nuclear envelope.
What is within the nucleus?
What are nuclear pores for?
protein import and RNA export.
What do nuclei vary in accordance with?
cell type and organism.
Where are chromosomes?
in distinct territories within the nucleus.
What occurs in the nucleolus?
rRNA synthesis and ribosomal subunits are assembled.
What does the nucleolus contain?
DNA encoding rRNAs.
What do nuclear speckles do?
stores splicing factors
What are Cajal bodies?
may assemble ribonucleoproteins required for splicing.
How many Cajal bodies in the nucleus?
one or a few
What are PML bodies?
promylocytic leukemia bodies.- contain chromatin remodeling enzymes and transcription factors.
What may organize all of the nuclear processes?
What does outer nuclear membrane continue to?
What is the nuclear lumen continuous with?
What is an NPC?
channel for transport of molecules between nucleus and cytoplasm.
What does nuclear lamina do?
provides physical support for nuclear envelope
What is nuclear lamina constructed from?
lamins- intermediate filament proteins
How does lamina connect to inner membrane?
lamina-associated integral membrane proteins
How does nuclear lamina organize replication and transcription?
by connecting to chromatin
What lacks lamina
yeast and other unicellular eukaryotes
Where is the nuclear lamina located?
beneath the inner membrane
How do small uncharged molecules transport between cytoplasm and nucleus?
pass through the membranes of the envelope
What is an NPC
nuclear pore complex
If too large, how to molecules pass from cytoplasm to nucleus?
through an NPC with passive or active transport
What is required for nuclear localization?
how do proteins enter and exit the nucleus
through nuclear pores
Where is information for nuclear import?
in a small portion of the transported protein
What is NLS?
nuclear localization signal0=- short stretch of amino acids that targets proteins to the nucleus.
How many steps to nuclear import?
what are the steps of nuclear import?
translocation into nucleoplasm (via RAN GTPase)
How is nuclear export mediated?
What is the most common Nuclear export sequence?
short stretches of amino acids rich in lucine
Nuclear export receptors....
bind proteins that contain NESs in the nucleus and transports them to the cytoplasm.
What controls the direction of nuclear transport?
What promotes hydrolysis of GTP by Ran?
What promotes exchange of GDP for GTP on Ran?
Where is Ran-GAP located?
Where is Ran-GEF located?
What is exported from the nucleus to the cytoplasm?
mRNAs, tRNAs, and ribosomal subunits
how is export of RNA mediated?
Is RNA export energy dependent?
How are ribosomal subunits exported?
assembled in the nucleolus and exported by exportin 1
Where is rRNA made?
What is imported to make ribosomal subunits?
What is required for ribosomal subunit export?
Ran/Exportin1 (Crm1) and Nmd3
What is involved in mRNA export?
NXF1/TAP is the mRNP receptor
What is mRNP?
mature mRNA and binding proteins
single strand of DNA containing genes and their regulator proteins
state of nuclear DNA and its associated proteins during interphase
copy of a duplicated chromosome
how is chromatin divided?
heterochromatin- densely packed
euchromatin- less packed. often undergoing transcription
when can chormosomes be seen
only during mitosis
What is a nucleosome?
subunit of chromatin shaped like a cylinder with DNA organized into 1 2/3 turns around the surface
What does a nucleosome contain
2 copies of each core histone H2A, H2B, H3, and H4.
Core DNA is..
146 bp found on core particles produced by prolonged digestion with MNase.
What is linker DNA?
8-114bp that is susceptible to early cleavage
How are histones modified?
methylation, acetylation, phosphorylation
What is histone code?
combination of specific histone modifications that define the function of local regions of chromatin
What does SWI-SNF do?
remodels chromatin to allow for binding of proteins to promoter regions.
What recruits SWI-SNF?
factors to the DNA
What allows SWI-SNF to carry out functions
What is a centromere?
constricted region of a chromosome that includes the site of attachment to the mitotic or meiotic spindle
How are chromosomes pulled to the poles?
via microtubules that indirectly attach at the centromeres
How are centromeres identified?
by a DNA sequence that binds specific proteins that link the chromosome to the cytoskeleton
What allows plasmids to segregate accurately at mitosis?
What mediates binding to microtubules?
protein complexes formed at CEN elements.
What are CEN elements?
CDE-I, II, III short conserved sequences
What is a telomere?
region of repetitive DNA at the end of the chromatid
What does a telomere do?
protects the chromosomes from degradation at gene ends
What happens to telomeres?
get shorter with each cell division
Where is telomerase expressed?
in actively dividing cells, not quiescent cells.
What does loss of telomeres result in?
How can escape for senescence occur?
if telomerase is reactivated
What causes telomeres to shorten in each cell division?
mutation in telomerase
What is FISH used for?
to detect chromosomal abnormalities
What is FISH?
florescent in situ hybridization- detect different alleles or DNA compositions at the chromosomal level
What is required for FISH?
labeled probe and a control
What is a polytene chromosome
chromosomes found at the interphase nuclei of flies
in polytene chromosomes what is DNA rich?
in polytene chromosomes what is DNA poor?
When do polytene chromosomes expand?
at sites of DNA expression
What is a chromosomal puff?
region in which chromosome fibers are unwound
What do puffs reflect?