MCB 2050 EXAM REVIEW (Answered)
2025/2026, 100% Verified. 494Q&A.
Nucleus
largest organelle, primary difference bt eu/prokaryotes
"control centre"
Nuclear 'compartmentalization'
nucleoplasm, nuclear matrix, nuclear envelope, nuclear lamina
Nuclear envelope
boundary bt cytoplasm and nucleus
nuclear pores
'doorways' in the nuclear envelope. Regulate transport in/out of nucleus
nucleolus
site of ribosome synthesis
nucleoplasm
ordered architecture: site where chromatin is found and where RNA processing takes place
nuclear matrix
fibrillar protein support 'mesh' (network); serves in structural support and chromatin scaffold
Nucleoid
A dense region of DNA in a prokaryotic cell.
differences bt pro and eukaryotes?
eukaryotes - larger, structurally and functionally more complex
'compartmentalization'
each organelle contains both unique and common factors for functioning (metabolism) biogenesis
(formation) maintenance and turnover
2 main nucleus functions
compartmentalization of the cellular genome and its activity
coordination of cellular activity
nucleus separation allows for:
unique (spatial and temporal) regulation of gene expression in eukaryotes
,Nuclear Structure: Nucleoplasm
fluid filled interior of the nucleus
>30 specialized subdomains
e.g., nucleolus - irregular, dense and granular in appearance. Function in ribosome production. Size
and number (1-5) varies with cellular metabolic activity.
Nuclear Structure: Chromosomes
during interphase are organized into discrete subdomains ('territories') within the nucleus
Nuclear organization: interchromosomal channels
regions bt subdomains that serve as barriers to prevent unwanted DNA-DNA and/or DNA-protein
interactions
Nuclear organization: Nuclear speckles
subdomains (appear as 'speckles' under fluroscence microscopy) where mRNA splicing factors are
concentrated (where mRNA processing occurs)
often located in interchromosomal channels next to transcription factories
numerous and highly dynamic - >50 can quickly move, grow, shrink depending on cellular need
Nuclear Structure: Nuclear matrix
insuluble fibrallar-like protein network ('mesh') distributed throughout the cytoplasm
analogous to the cytoskeleton network in the cytoplasm
cytoskeleton network: filament systems
microtubules, actin microfilaments and intermediate filaments
Microtubules
Spiral strands of protein molecules that form a tubelike structure
actin microfilaments
help with cell shape, locomotion, vesicle transport
-are constantly growing and shrinking
intermediate filaments
Threadlike proteins in the cell's cytoskeleton that are roughly twice as thick as microfilaments
Nuclear matrix: Role
maintains overall shape of nucleus (Structural)
serves as a 'scaffold' - organizes nuclear subdomains and anchoring protein factors
Nuclear structure: Nuclear envelope
,seperates te contents of the nucleus from the cytoplasm
barrier, regulates passage of molecules bt nucleus and cytoplasm
probides structural framework of the nucleus
Nuclear Envelope: main parts
membrane
lamina
pore complexes
Nuclear membranes
two (inner and outer) concentric phospholipid bilayers
inner and outer separated by nuclear envelope lumen (10-50nm)
serve as barriers to the passage of ions, solutes and macromolecules bt the nucleus and cytoplasm
outer nuclear membrane
continuous w rough ER
ribosomes attached to cytoplasmic surface of the outer membrane
nuclear envelope lumen is continuous w the ER lumen
inner nuclear membrane
unique protein composition (functionally distinct from outer membrane)
where do inner and outer membranes join?
nuclear pore complexes
Nuclear Lamina
A mesh-like array of protein filaments lining the inner surface of the nuclear envelope, provides it
mechanical support;
helps maintain the shape of the nucleus.
serves as a scaffold for attachment of chromatin and nuclear matrix to the nuclear envelope
ABC nuclear lamins
evolutionarily related to proteins that form the intermediate filaments in the cytoskeleton network
Human diseases caused by LAMIN mutations?
progeria - premature aging disease in children
nuclear lamina is destabilized, causing aberrant changes in nuclear envelope morphology
, Nuclear pore complex (NPC)
channels 'doorways' in the nuclear enveolpe
responsible for the regulated trafficking (import/export) of all substances bt the nucleus and
cytoplasm
3000-4000/nucleus
Nuclear Pore Complex (NPC)
Large, multiprotein structure, composed largely of nucleoporins (nups), that extends across the
nuclear envelope. Ions and small molecules freely diffuse through NPCs; large proteins and
ribonucleoprotein particles are selectively transported through NPCs with the aid of soluble
proteins.
nucleoporins (Nups)
a family of around 30 proteins, are the main components of the nuclear pore complex in eukaryotic
cells
NPC Central Scaffold
scaffold - integral-bound/trans membrane nucleoporins.
Anchors NPC to nuclear envelope.
Forms an aqueous central channel (20-40nm wide)
NPC FG nculeoproins
mostly hydrophilic polupeptides w short repeats of hydrophobic domains inriched in F and G (FG
domains)
unique, highly ordered structure - extended flexible 'mesh'
FG nucleoporins transport
small molecules move freely thru the NPC in either directions (e.g., nucleotides)
39 nm or 40 kDa is the limit for free diffusion
Molecules >40kDa unable to pass through freely, e.g., RNA and most proteins must be selectively
imported/exported by an active process
discovery of FG nup size-exclusion limit
discovered based on studies w microinjected gold particles of various size coated with nuclear
proteins
Y-complexes
cytoplasmic and nuclear rings
2025/2026, 100% Verified. 494Q&A.
Nucleus
largest organelle, primary difference bt eu/prokaryotes
"control centre"
Nuclear 'compartmentalization'
nucleoplasm, nuclear matrix, nuclear envelope, nuclear lamina
Nuclear envelope
boundary bt cytoplasm and nucleus
nuclear pores
'doorways' in the nuclear envelope. Regulate transport in/out of nucleus
nucleolus
site of ribosome synthesis
nucleoplasm
ordered architecture: site where chromatin is found and where RNA processing takes place
nuclear matrix
fibrillar protein support 'mesh' (network); serves in structural support and chromatin scaffold
Nucleoid
A dense region of DNA in a prokaryotic cell.
differences bt pro and eukaryotes?
eukaryotes - larger, structurally and functionally more complex
'compartmentalization'
each organelle contains both unique and common factors for functioning (metabolism) biogenesis
(formation) maintenance and turnover
2 main nucleus functions
compartmentalization of the cellular genome and its activity
coordination of cellular activity
nucleus separation allows for:
unique (spatial and temporal) regulation of gene expression in eukaryotes
,Nuclear Structure: Nucleoplasm
fluid filled interior of the nucleus
>30 specialized subdomains
e.g., nucleolus - irregular, dense and granular in appearance. Function in ribosome production. Size
and number (1-5) varies with cellular metabolic activity.
Nuclear Structure: Chromosomes
during interphase are organized into discrete subdomains ('territories') within the nucleus
Nuclear organization: interchromosomal channels
regions bt subdomains that serve as barriers to prevent unwanted DNA-DNA and/or DNA-protein
interactions
Nuclear organization: Nuclear speckles
subdomains (appear as 'speckles' under fluroscence microscopy) where mRNA splicing factors are
concentrated (where mRNA processing occurs)
often located in interchromosomal channels next to transcription factories
numerous and highly dynamic - >50 can quickly move, grow, shrink depending on cellular need
Nuclear Structure: Nuclear matrix
insuluble fibrallar-like protein network ('mesh') distributed throughout the cytoplasm
analogous to the cytoskeleton network in the cytoplasm
cytoskeleton network: filament systems
microtubules, actin microfilaments and intermediate filaments
Microtubules
Spiral strands of protein molecules that form a tubelike structure
actin microfilaments
help with cell shape, locomotion, vesicle transport
-are constantly growing and shrinking
intermediate filaments
Threadlike proteins in the cell's cytoskeleton that are roughly twice as thick as microfilaments
Nuclear matrix: Role
maintains overall shape of nucleus (Structural)
serves as a 'scaffold' - organizes nuclear subdomains and anchoring protein factors
Nuclear structure: Nuclear envelope
,seperates te contents of the nucleus from the cytoplasm
barrier, regulates passage of molecules bt nucleus and cytoplasm
probides structural framework of the nucleus
Nuclear Envelope: main parts
membrane
lamina
pore complexes
Nuclear membranes
two (inner and outer) concentric phospholipid bilayers
inner and outer separated by nuclear envelope lumen (10-50nm)
serve as barriers to the passage of ions, solutes and macromolecules bt the nucleus and cytoplasm
outer nuclear membrane
continuous w rough ER
ribosomes attached to cytoplasmic surface of the outer membrane
nuclear envelope lumen is continuous w the ER lumen
inner nuclear membrane
unique protein composition (functionally distinct from outer membrane)
where do inner and outer membranes join?
nuclear pore complexes
Nuclear Lamina
A mesh-like array of protein filaments lining the inner surface of the nuclear envelope, provides it
mechanical support;
helps maintain the shape of the nucleus.
serves as a scaffold for attachment of chromatin and nuclear matrix to the nuclear envelope
ABC nuclear lamins
evolutionarily related to proteins that form the intermediate filaments in the cytoskeleton network
Human diseases caused by LAMIN mutations?
progeria - premature aging disease in children
nuclear lamina is destabilized, causing aberrant changes in nuclear envelope morphology
, Nuclear pore complex (NPC)
channels 'doorways' in the nuclear enveolpe
responsible for the regulated trafficking (import/export) of all substances bt the nucleus and
cytoplasm
3000-4000/nucleus
Nuclear Pore Complex (NPC)
Large, multiprotein structure, composed largely of nucleoporins (nups), that extends across the
nuclear envelope. Ions and small molecules freely diffuse through NPCs; large proteins and
ribonucleoprotein particles are selectively transported through NPCs with the aid of soluble
proteins.
nucleoporins (Nups)
a family of around 30 proteins, are the main components of the nuclear pore complex in eukaryotic
cells
NPC Central Scaffold
scaffold - integral-bound/trans membrane nucleoporins.
Anchors NPC to nuclear envelope.
Forms an aqueous central channel (20-40nm wide)
NPC FG nculeoproins
mostly hydrophilic polupeptides w short repeats of hydrophobic domains inriched in F and G (FG
domains)
unique, highly ordered structure - extended flexible 'mesh'
FG nucleoporins transport
small molecules move freely thru the NPC in either directions (e.g., nucleotides)
39 nm or 40 kDa is the limit for free diffusion
Molecules >40kDa unable to pass through freely, e.g., RNA and most proteins must be selectively
imported/exported by an active process
discovery of FG nup size-exclusion limit
discovered based on studies w microinjected gold particles of various size coated with nuclear
proteins
Y-complexes
cytoplasmic and nuclear rings
