Lesson 15: The Nucleus

nuclear pores

_______ ______ allow proteins and mRNA to move between the nucleus and cytoplasm

2

the nucleus is surrounded by ___ membrane bilayer(s)

ER, lumen

the outer membrane of the nucleus is continuous with the _____, meaning they share the same ______

nuclear lamins

the ______ ______ form a basket-like network of filaments that protect nucleus from mechanical forces

intermediate, eukaryotic

nuclear lamins are _______ filaments in the nucleus of all ________ cells

mechanical, chromosomes, interphase

Lamins:

1. protect the nucleus from _________ forces

2. provide an attachment site for _________ during ________

3. likely contribute to gene expression in some way

lamins, nucleus

Mutations in ______ cause Hutchinson-Gilford syndrome (progeria):

-symptoms of premature aging

-altered by a single amino acid residue

-causes an abnormal shape of the _______

rRNA

10 chromosomes contribute a loop of ______ genes to the nucleolus

fluorescence in situ hybridization

_______ __ ____ ________ allows for the visualization of chromosomes by microscopy:
1. probe used to label, DNA denatured

2. fluorescent molecs attach to ssDNA, ssDNA attaches to target

interphase

________ chromosomes occupy distinct territories within the nucleus

regulation, recombination, epigenetic

Advantages of Chromosome Territories:

1. independent gene _________: diff based on local nuclear environment, one copy may be near activative transcription factors whil ethe other copy may be near repressive heterochromatin

2. Prevents inappropriate __________: keeping homologs apart reduces risk of out of place recombination in somaticcells, should not be occurring in regular body cells, but proximity increases the chance of DNA breaks triggering recombination

3. Maintains distinct _______ states: maintains diff chromatin modifications without interference (like imprinted genes or X-inactivation

cytoskeleton

-lamins are proteins that are part of the __________

-maintains nuclear shape when cell deforms

-protects chromatin

False

True or false: the nucleolus has a membrane

-5 diff chromosome pairs come together

-synthesize ribosomal components

-churns out ribosomes

noncoding, doesn’t

“Junk” DNA is (coding/noncoding) DNA that (does/doesn’t) provide instructions for making proteins

-regulates some genes

-controls 3D chromos structure

-prod noncoding RNA molecules (tRNA/rRNA)

-some may still be non-functional

nucleosomes, 8, H1

________ are the basic units of eukaryotic chromosome structure

-contain DNA wrapped around a protein core of ____ histone molecules

-histone ___ provides additional packaging of nucleosomes in the chromatin fiber by acting as a linker between the DNA and nucleosome - makes more compact

cohesins, condensins, DNA

SMC Ring Complex: molecular motor that windds DNA into loops

-_______: organize interphase chromatin

-______: Chromos → mitotic chromosome (before cell division)

-ATP hydrolysis to “walk” along fiber of ____

2

Steps of SMC Complex ATP hydrolysis:

Hydrolyzes __ ATP

1. hinge attaches to DNA, threads through SMC complex

2. 2 ATP attaches to the ATPase domain end

3. hydrolyzes, releases 2 Phoshate ions

4. stretches region further down DNA, 2 ADP leave so it returns to original state, effectively inchworming down the line of DNA to create a loop between the ATPase domain and the hinge

clamp

Size of chromatin loops is regulated by sequence-specific _____ proteins:

-cohesin binds and creates loop until two clamps hit each other

-cohesins are stuck in the loop, do not detach, but do not do anything

condensins

______ form loops within preexisting loops from cohesins, folding amitotic chromosome into a compact configuration

-when cells enter mitosis, most cohesins organized by an interphase chromosome are replaced by the condensins

-Condensin II forms initial large chromatin loops, condensin I forms second set of loops inside them

interphase

cohesins are used during ______

M phase

condensins are used during _____

many, 1, 2

Each chromosome has (one/many) origins of replication _ centromere, and _ telomeres

Packing

Levels of DNA ______:

1. DNA Double helix

2. “Beads on a string” chromatin (nucleosomes)

3. chromatin fiber of associated nucleosomes

4. folded into loops by cohesins

5. condensed further into chromosome by condensins

ATP

ATP-dependent chromatin-remodeling complexes (REGULATE CONDENSED CHROMATIN):

-How to access? locally reposition the DNA wrapped around the nucleosomes instead of unraveling!

-use ____ hydrolysis to shift position

Histone

_______ tail post-translational modification:

-methylated, acetylated, phosphorylated (promote condensation or expansion of chromatin)

-modifications made by “writers”, removed by “erasers”, and acted on by “readers'“

heterochromatin

_____: highly condensed interphase chromatin containing “silent” genes that aren’t expressed

facultative, constitutive

_______: temporarily condensed chromatin

_______: permanently condensed (centromeres, telomeres)

euchromatin

_____: less condensed interphase chromatin, genes actively expressed

-QUIESCENT ________: decondensed but not actively transcribing anything (“QUIEt”)

Spread

Reader-Writer Complexes ______ Heterochromatin until it reaches a barrier sequence

X

Chromatin Regulation: One __ chromosome is inactivated, silencing the genes of the entire chromosome:
-women born with a maternal and paternal X chromos, one of them is randomly inactivated and the active one is passed on to offspring

yes

epigenetic inheritance: can heterochromatin be inherited after DNA replication?