Lecture 2 - nucleus Flashcards
What is the largest organelle?
nucleus
Does nuclear size vary between organisms and cell-to-cell?
yes
When does the nuclear size increase?
during development and in cancer cells
What is the difference in the nucleus between eukaryotes and prokaryotes?
euk possess membrane bound nucleus, larger, structurally and functionally more complex interiors, cellular compartmentalization
prok possess a region (nucleiod) where chromosome is located; less DNA, less DNA packaging, and limited to no RNA processing
What are the two main functions of the nucleus?
- compartmentalization of the cellular genome and its activities
- coordination of cellular activities
What does separation of the cytoplasm from the genome allow for?
spatial and temporal regulation of gene expression in eukaryotes
When are mRNA’s translated in euk vs prok?
prok - mRNA translated while txn is in progress
euk - mRNAs undergo post-tnl processing before being transported out of the nucleus and then translated in cytoplasm or at ER
Which has more gene expression control, euk or pro?
euk, the nuclear envelope limits access of txn factors from cytoplasm to genome
What is the nucleoplasm?
fluid-filled interior of the nucleus, highly organized
How many subdomains does the nucleoplasm have?
over 30 specialized subdomains that participate in specific functions
Are nuclear subdomains membrane bound?
no
What is the nucleolus?
subdomain in the nucleoplasm
What are some physical characteristics of the nucleolus?
irregular shaped, dense and granular in appearance
How many nucleoli are in the nucleus?
(1-5) size and number depend on metabolic activity of the cell
What is the relationship between nucleoli and cellular metabolism?
as cellular activity increases, protein synthesis increase and the size/number of nucleoli increases
What is the function of the nucleolus?
producing ribosomes
- site of ribosomal DNA gene txn, rRNA processing and initial stages of ribosomal subunit assembly
Where does the final assembly of ribosomes take place?
cytoplasm
How are chromosomes organized in the nucleus during interphase?
discrete subdomains, location of gene is often related to its activity
What are interchromosomal channels?
regions between chromosome subdomains that serve as barriers to prevent unwanted DNA-DNA and or DNA protein interactions
What are transcription factories?
active genes from different subdomains extend into interchromosomal channels to form txn factories where txn factors are concentrated
What are interchromosomal interactions?
“kissing chromosomes” - gene regulatory regions from one chromosome activate genes on another chromosome
What are nuclear speckles?
subdomain of the nucleus, where mRNA splicing factors are concentrated
Where are nuclear speckles located?
in the nucleus, often in interchromosomal channels next to transcription factories
What is a unique characteristic of nuclear speckles?
numerous and highly dynamic - often move quickly and grow/shrink and change in number depending on needs of the cell
What is the nuclear matrix?
nuclear subdomain, insoluble fibrillar-like protein network (mesh) distributed throughout nucleoplasm - analogous to cytoskeleton network in cytoplasm
What are the functions of the nuclear matrix?
structural role - maintains overall shape of nucleus
serves as scaffold - responsible for organizing nuclear subdomains and anchoring protein factors
What is the nuclear envelope?
nuclear subdomain, “outside of nucleus”, separates the contents of the nucleus from surrounding cytoplasm
What is the function of of nuclear envelope?
barrier - requires regulated passage of molecules between nucleus and cytoplasm
establishes unique composition of nucleus and spatially regulates gene expression
provides structural framework for nucleus
What are the three parts of the nuclear envelope?
nuclear membranes
nuclear lamina
nuclear pore complex
What are the nuclear membranes?
part of the subdomain nuclear envelope, there are two membranes, inner and outer, arranged in parallel, they are phospholipid bilayers
What are the inner and outer nuclear membranes separated by?
nuclear envelope lumen (10-50 nm diameter)
What is the function of the nuclear membranes?
serve as barriers to passage of ions, solutes and macromolecules between nucleus and cytoplasm
How do the outer and inner membrane come together in the event of a nuclear pore?
a nucleoprotein joins them
What is the outer nuclear membrane continuous with?
rough endoplasmic reticulum
What are attached to the outer nuclear membrane?
ribosomes
What is the nuclear envelope lumen continuous with?
the er lumen
is the inner nuclear membrane continuous with anything?
no, it has a unique protein composition
What is the nuclear lamina?
part of the subdomain nuclear envelope, network of mesh long, filament-like proteins
What are ABC nuclear lamins evolutionarily related to?
proteins that form intermediate filaments in cytoskeleton network
What is the function of the nuclear lamina?
mechanical support
serves as scaffold for attachment of chromatin and nuclear matrix to nuclear envelop
What is the consequence of a mutation in the LAMIN gene
mutation in the nuclear lamina
hutchinson gilford progeria syndromes
- premature aging in children
- point mutation in LAMIN A gene leading to truncated lamin protein
- results in destabilization of nuclear lamina
What is the nuclear pore complex?
subdomain of the nuclear envelope, they are channels in the nuclear nevelope
What is the function of NPC’s?
regulating trafficking (import and export) of all substances between nucleus and cytoplasm such as small polar molecules, RNAs, and proteins
How many NPC’s per nucleus?
3000-4000, number of NPC’s related to nuclear activity
Is the placement of NPC’s random?
no
How many proteins make up the NPC?
about 40 different proteins
What are nucleoporins (Nups)?
proteins that make up the NPC
Are nups conserved?
yes
What is the general structure of an NPC?
8-fold symmetrical structure
central scaffold
FG nucleoporins
Y-complexes
cytoplasmic filaments
nuclear basket
What is the central scaffold and its function?
a part of the NPC
- composed of integral trans membrane bound nucleoporins
- anchors NPC to nuclear envelope membranes
- forms aqueous central channel - 20-40 nm wide
What are FG nucleoporins and their function?
part of the NPC
- inner surface is lined by them
- possess unusual AA comp
- FG domains extend into central channel (forms mesh that limits diffusion of macromolecules larger than 40 kDA
- small molecules move freely through NPC in either direction
What is the structure of an FG nucleoporin?
hydrophilic polypeptides with short repeats of hydrophobic domains enriched in phe and gly - FG domains
What are Y-complexes?
a part of the NPC
- includes cytoplasmic ring and nuclear ring
- composed of structural Nups
- linked to central scaffold and cytoplasmic filaments
Where are Y-complexes located?
NPC’s
- cytoplasmic and nuclear side of NPC
What are cytoplasmic filaments?
part of the NPC
- long filament shaped Nups that extend into the cytoplasm
- involved in nuclear receptor cargo protein recognition and import from the cytoplasm
What is the nuclear basket?
part of the NPC
- basket like structure located on nuclear side of NPC
- linked to y-complez nuclear ring
What is the funtion of the nuclear basket?
nuclear receptor-cargo protein import and export to cytoplasm
