Lecture 2 - nucleus Flashcards by Arden Pappot

What is the largest organelle?

nucleus

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Does nuclear size vary between organisms and cell-to-cell?

yes

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When does the nuclear size increase?

during development and in cancer cells

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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

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What are the two main functions of the nucleus?

compartmentalization of the cellular genome and its activities
coordination of cellular activities

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What does separation of the cytoplasm from the genome allow for?

spatial and temporal regulation of gene expression in eukaryotes

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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

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Which has more gene expression control, euk or pro?

euk, the nuclear envelope limits access of txn factors from cytoplasm to genome

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What is the nucleoplasm?

fluid-filled interior of the nucleus, highly organized

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How many subdomains does the nucleoplasm have?

over 30 specialized subdomains that participate in specific functions

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Are nuclear subdomains membrane bound?

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What is the nucleolus?

subdomain in the nucleoplasm

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What are some physical characteristics of the nucleolus?

irregular shaped, dense and granular in appearance

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How many nucleoli are in the nucleus?

(1-5) size and number depend on metabolic activity of the cell

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What is the relationship between nucleoli and cellular metabolism?

as cellular activity increases, protein synthesis increase and the size/number of nucleoli increases

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What is the function of the nucleolus?

producing ribosomes
- site of ribosomal DNA gene txn, rRNA processing and initial stages of ribosomal subunit assembly

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Where does the final assembly of ribosomes take place?

cytoplasm

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How are chromosomes organized in the nucleus during interphase?

discrete subdomains, location of gene is often related to its activity

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What are interchromosomal channels?

regions between chromosome subdomains that serve as barriers to prevent unwanted DNA-DNA and or DNA protein interactions

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What are transcription factories?

active genes from different subdomains extend into interchromosomal channels to form txn factories where txn factors are concentrated

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What are interchromosomal interactions?

“kissing chromosomes” - gene regulatory regions from one chromosome activate genes on another chromosome

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What are nuclear speckles?

subdomain of the nucleus, where mRNA splicing factors are concentrated

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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?

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