BIOL 315 Cell Bio Quiz 3

Diameter of microtubules

25nm

Diameter of microfilaments

7nm

Diameter of Intermediate filaments

8-12nm

Subunits of microfilaments (before binding)

G - actin

cells are chemically preserved, then labeled with fluorescent compounds that bind to the cytoskeletal proteins (such as antibodies), causing them to glow in the fluorescence microscope

fluorescence microscopy on fixed specimens

fluorescent version of cytoskeletal proteins are made and introduced into living cells, which are then observed under the fluorescence microscope and digitally recorded

live cell fluorescence microscopy

high resolution images from a video or digital camera (attached to a microscope) are processed by computers to increase contrast and remove background features

computer enhanced digital video microscopy

can resolve individual filaments; cells prepared by thin section, quick freeze deep-etch, or direct mount techniques

electron microscopy

microtubules that pervade the cytoplasm to maintain or alter cell shape, construct mitotic and meiotic spindles, and serve as tracks for motor proteins to walk vesicles and organelles

cytosolic microtubules

microtubules located in cell surface projections such as cilia and flagella, generating cell motility or sweeping fluid/mucus across epithelial surfaces

axonemal microtubules

globular protein subunits of microtubules. they fold similar and bind together. Each has an N-terminal GTP-binding domain and a C-terminal that interacts with microtubule-associated proteins (MAPs)

alpha and beta tubulin subunits

The fundamental building block of microtubules, consisting of one alpha-tubulin and one beta-tubulin subunit tightly bound together in a specific, non-covalent, head-to-tail orientation

tubulin heterodimer

Closely related structural variants of $\alpha$- and $\beta$-tubulin encoded by distinct genes within an organism

tubulin isoforms

(in microtubules) A longitudinal, linear array of alternating alpha- and beta-tubulin heterodimers stacked head-to-tail

protofilament

fast growing end of a microtubule where beta-tubulin is exposed; lower critical concentration for dimer addition

plus end

slow-growing or anchored end of a microtubule where alpha-tubulin is exposed; higher critical concentration for dimer addition

minus end

A single hollow cylinder composed of 13 complete protofilaments (found in cytosolic microtubules)

singlet

One complete 13-protofilament ring (A tubule) fused to an incomplete 10–11 protofilament ring (B tubule); characteristic of axonemal cilia and flagella

doublet

One complete 13-protofilament ring (A tubule) fused to two incomplete rings (B and C tubules); characteristic of basal bodies and centrioles

triplet

The initial, slow phase of microtubule assembly where individual tubulin heterodimers coalesce into small, unstable clusters called oligomers (which serve as "seeds")

nucleation

The rapid growth phase where tubulin heterodimers are rapidly added onto the ends of existing oligomers or growing microtubule ends

elongation

The steady-state phase where free tubulin dimer concentration drops, balancing the rate of dimer addition and disassembly

plateau phase

The threshold concentration of free tubulin heterodimers required for microtubule assembly. Growth occurs above it, while disassembly occurs below it

critical concentration

A phenomenon occurring when the free tubulin dimer concentration is above the critical concentration for the plus end but below that for the minus end. Heterodimers are continuously added to the plus end while simultaneously detaching from the minus end, making the microtubule appear to "walk" or move through space without changing its overall length

treadmilling

A stabilizing region of GTP-bound tubulin heterodimers at the growing plus end of a microtubule that protects it from disassembly

GTP Cap

The continuous alternation between rapid microtubule growth and sudden shrinkage driven by GTP hydrolysis

dynamic instability

In microtubules, the sudden, rapid disassembly and peeling apart of protofilaments caused when GTP hydrolysis catches up to the growing tip and the protective GTP cap is lost

catastrophe

The abrupt transition from catastrophe back to growth when a new GTP cap is re-established by adding fresh GTP-bound tubulin dimers

rescue

Drugs that bind to free tubulin heterodimers (beta-tubulin) to prevent dimer addition, destabilizing microtubules and promoting disassembly/catastrophe to block cell division

colchicine, vinblastine, nocodazole

A chemotherapy drug that binds to beta-tubulin in GDP-bound heterodimers and forces their shape to mimic GTP-bound heterodimers, preventing dissociation by “freezing” microtubules in place. This prevents cancer cell division

taxol

binds at regular intervals along the microtubule wall and interacts with other structures and filaments. it can bundle microtubules together

MAP (tau)

proteins that capture and stabilize the growing ends of a microtubule

+- TIP proteins (EB1)

proteins that promote depolarization or peeling apart of subunits of microtubules

catastrophins (MCAK)

3 functions of microfilaments

cell movement, cell shape, molecule movement

muscle actin

alpha actin

nonmuscle actin

beta and gamma actin

the plus end of a microfilament is ____

barbed

the minus end of a microfilament is ____

pointed

(drug) fungal metabolites that prevent the addition of new monomers to existing microfilaments. Filaments eventually depolymerize

cytochalasins

(drug) toxin that sequesters actin monomers and prevents them from adding to microfilaments

latrunculin A

(drug) stabilizes microfilaments and prevents them from depolymerizing

phalloidin

architecture of actin - made of stress fibers

contractile bundle

architecture of actin - crosslinks just beneath the plasma membrane

gel

architecture of actin - branched network used for movement

lamellipodium

architecture of actin - parallel bundle used for movement

filopodium

regulatory protein that binds and sequesters free G-actin to slow down microfilament assembly

thymosin beta 4

regulatory protein that binds free G-actin but does not sequester it

profilin

regulatory protein that binds the end of a microfilament to prevent further loss or addition of subunits

capZ

regulatory protein that moves along the end of a growing microfilament and promotes polymerization

formins

regulatory protein that nucleates new branches on the sides of existing microfilaments, activated by WASP proteins

Arp 2/3

structures of crosslinked microfilaments that increase the surface area of intestinal mucosal cells

microvilli

regulatory protein that “splices” together overlapping microfilaments to form crosslinks

filamen

proteins that bundle microfilaments in microvilli

fimbrin and villin

network of filaments connected to the base of microvilli

terminal web

main type and function of intermediate filaments

keratin, mechanical strength

subunit of intermediate filaments

variable

name for building block unit of intermediate filaments; these are bundled together to form long filamentous structures

protofilament

linker protein that connects intermediate filaments, microfilaments and microtubules

plectin

primary MTOC, located near the nucleus; nucleates, organizes, and anchors the minus ends of cytosolic microtubules, acting as the focal point for the microtubule network and the mitotic spindle during cell division

centrosome

individual, barrel shaped structural subunit located inside the centrosome; it has a cylindrical wall made of 9 triplet microtubules, and there are two of them positioned perpendicular to each other at a right angle

centriole

motor protein that transports vesicles toward the plus end of microtubules near the cell periphery

kinesin

motor protein that transports vesicles toward the minus end of microtubules near the cell center

cytosolic dynein

region that binds cytoskeletal filaments and hydrolyzes atp to generate mechanical force (blue)

motor domain

coiled-coil region connecting the filament-binding heads to the cargo-binding tail (gray)

stalk domain

carboxy-terminal region that attaches to specific cellular cargo or vesicles (purple)

tail domain

protein assembly that connects cytosolic dynein to membrane-bound cargo (green)

dynactin complex light chain

microtubule-based movement of vesicles along the long axon of a neuron

fast axonal transport

short, abundant cell projections that beat like oars to move fluid across tissue surfaces

cilia

long, scarce cell projections that move with a wave-like motion to propel a cell through fluid

flagella

microtubule-based structural core inside cilia and flagella arranged in a 9+2 pattern

axoneme

microtubule-organizing center at the base of cilia and flagella made of nine triplet microtubules

basal body

motor protein attached to outer doublets that generates sliding forces to bend the appendage

axonemal dynein

structural bridges projecting inward from outer doublets to translate microtubule sliding into bending (gray)

radial spokes

protein bridge connecting adjacent outer doublets to limit sliding and enforce structural bending (purple)

nexin linker

asymptomatic condition where all internal organs are mirrored left-to-right due to ciliary defects

sinus inversus totalis

severe developmental condition where only some internal organs are reversed in orientation

heterotaxy

multi-step process where a cell crawls over a substrate via protrusion, adhesion, and contraction

cell migration

transmembrane proteins that link internal actin filaments to extracellular matrix proteins

integrins

attachment complexes anchored by integrins that connect the cell to the substrate

focal adhesions

regulatory enzyme that controls the assembly and turnover of attachment sites in cell migration

focal adhesion kinase

actin-based motor protein superfamily that hydrolyzes atp to exert force or contract microfilaments

myosin

rearward translocation of actin filaments from the leading edge powered by polymerization and motor activity

retrograde flow

motor protein activated by rho at the cell rear to drive cell body contraction and detachment

nonmuscle myosin ii

polarized sheets of cells with discrete apical and basal functional domains

epithelium

loosely organized connective tissue cells attached to each other or a rigid matrix

mesenchymal cells

cell connections that anchor the cytoskeleton to the plasma membrane and link adjoining cells

adhesive junctions

cadherin-mediated cell-cell junctions anchored internally to actin microfilaments

adherens junctions

calcium-dependent transmembrane proteins that zip together extracellularly to bind neighboring cells

cadherins

cytosolic linker proteins like alpha and beta variants that connect cadherins to actin microfilaments

catenins

process where structured cell sheets lose adhesion and transform into mobile, loosely organized cells

epithelial-mesenchymal transition

button-like points of strong cell-cell adhesion abundant in tissues under mechanical stress

desmosomes

cytosolic plaque protein that anchors intermediate filaments like keratin

desmoplakin

beta-catenin family protein that binds desmosomal cadherins to desmoplakin (red)

plakoglobin

cell-cell seals that eliminate extracellular space and prevent molecule movement between cells

tight junctions

integral membrane proteins with four transmembrane domains that form sealing ridges (pink)

claudins

transmembrane protein that aids in forming permeability barriers between cells in tight junctions

occludin

intercellular regions where aligned plasma membranes allow direct passage of small molecules and ions

gap junctions

hollow cylindrical channel in an intercellular junction formed by six protein subunits

connexon

protein subunit that assembles into six-member rings to form passage channels between cells in gap junctions

connexin

network of structural proteins and polysaccharides providing strength and support to tissues

extracellular matrix