Cytoskeleton

cytoskeleton

internal framework of the cell extending throughout the cytoplasm

• represents 25-35% of the total cell proteins

• made of microfilaments, intermediate filaments, and microtubules

microfilaments

AKA actin filaments

• concentrated beneath the plasma membrane

• thin and flexible

• made of 2 helically wound strands of polymerized actin monomers

• functions: plasma membrane support, endocytosis, exocytosis, cell motility

• DYNAMIC

globular

type of actin that is bound to ATP and added to the growing (+) end

filamentous

type of actin that id ADP bound and removed from the depolarizing (-) end

ATP

the assembly/disassembly of microfilaments is ___ dependent

cell motility

the polymerization/growing of microfilaments against the plasma membrane pushes against it and aid in ____ aka movement

functions of microfilaments

• aid in synaptic vesicle trafficking in presynaptic terminal

• provide support and shape for the plasma membrane

• provide anchors for transmembrane proteins

• regulate & support dendritic spine morphology

• provide growth guidance for axons in growth cones

spectrin

microfilaments provide shape and support to the plasma membrane by binding to ___ cross-linked filaments

ankyrin

microfilaments provide anchors for transmembrane proteins by binding to the protein ___ which links the transmembrane proteins to the microfilament network

actin-myosin II, dynamin

___ form a cage-like structure around the nascent endosome and promote membrane tension, while ___ is the protein cutting the new vesicle’s connection to the plasma membrane

dendritic spines

microfilaments form a mesh-like structure inside ___ to stabilize their growth and shape with their rapid polymerization/depolymerization able to respond to the rapid adaptation to signals ___ are subjected to.

AMPA, NMDA

actin-associated proteins are regulated by the calcium (Ca2+) influx caused by the ___ and ___ receptors

intermediate filaments

AKA neurofilaments

• most resilient/tough/durable

• STABLE

• 8-12 nm diameter

• fibrous proteins supercoiled into thicker cable

• specific to the tissues

• maintain cell shape and organelles’ position

neurofilament triplet proteins

• NF-L

• NF-M

• NF-H

structurally related proteins making up the bulk of neurofilaments. They all form alpha helices, and they have a variable C-terminal domain that is longer the heavier the protein is.

nestin

protein expressed in neurofilaments during development

central neurons

___ express mostly internexin and neurofilament triplet proteins

NF-H

high molecular weight protein in neurofilaments

NF-M

middle molecular weight protein in neurofilaments

NF-L

low molecular weight protein in neurofilaments

pH, temperature, ionic strength

neurofilaments assembly is NOT energy dependent, but it does depend on __, __, ___.

dimers, tetramers

neurofilament monomers initially form __, which then assemble into anti-parallel __, and 8 of those assemble into an 8-12nm diameter unit.

phosphorylation

___ of neurofilaments predominate in larger diameter axons for support, to resist the force of myelin wrapping.

• ___ occurs on lysine residues in NF-H and NF-M tail domains

cross-bridges

When the variable C-terminal tail/domain of NF-H and NF-M gets phosphorylated, it forms ___ between neurofilaments and microtubules allowing neurofilaments to immobilize themselves and stabilize the axon/axon caliber.

neuroblast

the neurofilament proteins expressed in the ___ are vimentin and nestin

mature neuron

the neurofilaments proteins expressed in a ____ are the triplet NF proteins and internexin

microtubule

• hollow tubes made of tubulin

• LARGEST

• DYNAMIC

• provide pathways/tracks for intracellular transport

• aid in extension process during development

• establish neuronal polarity & maintain cell shape

alpha-beta tubulin

microtubules are made of protofilament rings, which are made of ____ dimers

GTP

microtubule assembly is ___ dependent

growing +

GTP binds at the ___ end of microtubules

disassembling -

GDP binds to the __ end of microtubules

microtubule-organizing center

aka MTOC

• organize and orient microtubule network

• localized in the cell soma

terminal, cell body

microtubules are polar, and in the axon, the positive end is toward the ___ while the negative end is toward the ___

mixed

microtubules are polar, and in the dendrites, they have __ polarity aka bidirectional traffic

alpha-tubulin

stability of microtubules depends on post-translational modifications of ___

• tyrosinated ___ = dynamic microtubule

• acetylated/de-tyrosinated ___ = stable microtubule

microtubule-associated proteins

aka MAPs

stabilize/regulate microtubule assembly

• MAP1 = axon, dendrite, cell body

• MAP2 = dendrite and cell body only

• Tau = axon only

Tau

__ regulates microtubule spacing

• hyperphosphorylated or post-translationally modified = dissociate/stick out from microtubules

• aggregates into NFTs and involved in Alzheimer’s disease

neurofibrillary tangles

Tau in diseases like Alzheimer’s can aggregate in ___ aka NFTs when abnormally phosphorylated, causing cell death and dysfunction.

• made of helical stack of C-shaped Tau subunits

• cross-beta structure

functions of microtubules

• intracellular transport

• maintain cell shape

• establish neural polarity

• aid in extension during development

functions of neurofilaments

• maintain cell shape

• axonal support

• anchors organelles