Cell and Molecular Bio Exam 4

cytoskeleton

structure that supports cell shape and motion

functions of cytoskeleton

keep cell shape, mediate cytokinesis, pull apart chromosomes during cell division, motion, muscle cell contraction, intracellular vesicular trafficking

cytoskeletal filaments

make up cytoskeleton and made up of individual protein monomer components

why can cytoskeletal filaments assemble and/or disassemble easily and rapidly?

they are linked together by weak, non-covalent interactions

what are the three types of filaments

actin filaments, microtubules, intermediate filaments

filaments depend on ____ to perform

accessory proteins that link the filaments to other cell components and to each other

actin filaments

flexible 5-9 nm thick, composed of two-stranded helix made of acitn protein monomers

function of actin filaments

determine shape of cell's surface and mediate cell movement

microtubules

25 nm thick, hollow cylinders made up of tubulin protein monomers; usually attached to a centrosome near the nucleus; make up cilia and flagella on cell's surface

function of microtubules

chromosomal segregation, determine position of membrane-bound organelles and direct intracellular transport

intermediate filaments

ropelike filaments 10 nm thick made up of intermediate filament proteins and extend in circular protein

function of intermediate filaments

strengthen epithelium, provide mechanical strength and resistance to shear stress

protofilaments

string that cytoskeletal filaments assemble into and are thermally unstable5

time course

pattern in which polymerization of filaments follow

tubulin subunits are ___

heterodimers

how are alpha and beta tubulin subunits held together

non-covalent bonds

plus end of filament

more dynamic end where both growth and shrinkage takes place faster

minus end of filament

where growth and shrinkage take place slower

treadmilling

the minus end of the filament is shrinking and the plus end is growing which makes it appear as it is moving

dynamic instability

the continuous growth and shrinking that takes place on the plus and minus end of the filament individually (continuous sequence of rescue and catastrophe)

rescue

individual act of filament growth that occurs when the GTP cap is regained

catastrophe

individual act of filament shrinkage that occurs when the GTP cap is lost

A growing microtubule has a ____ which provides stability. The rest of subunits have ____ bound, making them less stable

GTP-cap, GDP

_______ and ________ allow subunits to be continously recycle and permit microtubules and actin to be continously remodeled

dynamic instability, treadmilling

MAP proteins

accessory proteins that stabilize the end of growing microtubules by binding to the plus end (rescues increase)

catastrophin proteins

accessory proteins that destabilize the end of growing microtubules by disassembling the plus end (catastrophes increase)

centrosome

major microtubule organizing center (MTOC) of the cell

how can microtubules find the center of the cell independently?

when a piece of a cell is cut off, the microtubules in the cell reorganize themselves and form a MTOC without centrioles and arrange themselves to form the "star-like" shape even in the absence of the nucleus

MAP2 proteins

accessory proteins that binds two microtubules and keeps them organized in a lattice

Tau proteins

accessory protein that bind along a single microtubule acting as a spacer (tighter spacing between microtubules)

toxins

affect filament assembly by binding filaments or bind free actin and tubulin subunits to prevent them from assembling

intermediate filaments

prominent in cells subject to mechanical stress; not easy to break

keratins are ____

intermediate filaments

plectin

cross-links intermediate filaments to other microtubules and myosin to the interior of the cell membrane

Mutations in the genes that encode proteins can cause diseases whose pathology consists of _____.

blistering, muscular distrophy, neurodegeneration

_____ can be arranged in different types of arrays depending on its function within the cell

actin

What three different arrays can actin bundles form

stress fibers, cell cortex, filopedia

stress fibers

actin is arranged in contractile bundles

cell cortex

actin filaments are arranged in a gel-like network

filopedia

actin filaments are arranged in tight parallel bundles

contractile bundles

actin filaments are spaced by cross linking proteins called alpha-actinin

parallel bundles

actin filaments are spaced by cross linking proteins called fimbrin

villin

cross-linking protein that packs actin filaments very close together in microvilli

microvilli

projections of the epithelium that increase the absorption surface of cells

focal adhesion contacts

connects stress fibers (peripheral actin filaments) to integrins

integrins

transmembrane adhesion proteins

vinculin

adaptor protein that attaches integrins to actin in focal adhesion contacts

actin staining shows _____ and vinculin staining shows ____

actin filaments, location of focal adhesion contacts

quiescent cells

cells that do not receive much stimulation and have actin filaments in the cortex and few focal adhesion contacts

RHO activated cells

rapidly assemble in prominent stress fibers and show many focal adhesion contacts

RAC activated cells

form large lamellipodia that extend the entire circumference of the cell and don't require focal adhesion contacts

Cdc42 activated cells

develop long filopodia at the cell periphery that form focal adhesion contacts with the substrate

RHO, RAC, and Cdc42 are _____

GTPases

molecular motors

proteins that bind the cytoskeleton and use energy from ATP to move along filaments
- exist in eukaryotic cells
- carry membrane-enclosed organelles (mitochondria, golgi, secretory vesicles)

myosin II

elongated protein formed from two heavy chains and four light chains and mediates muscle contraction

myosin light-chain kinase (MLCK)

enzyme that phosphorylates myosin light chain

two effects of MLCK

1) change in conformation of myosin head exposing actin-binding site
2) release of myosin tail from stick path on myosin head

myosin spontaneously assembles into _____ once activated by MLCK

bipolar filaments

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cont. from slide 35 lecture 17

myosin II bipolar filaments structure

- heads project outside
- bare zone - central portion without myosin heads

function of myosin heads

move actin filaments spontaneously with addition of ATP; almost all walk toward + end, contain motor domain

All myosins have highly conserved _______. The tails domains in the C-terminus and the N-terminus ends

motor domains

Myosin II mediates ______ in vertebrates.

muscle contraction

Myosin VI is the only one that walks toward the _______ of acting filaments

minus end

kinesins an dyneins are _____ that walk on microtubules.

molecular motors

kinesins

family of motor proteins

both myosin II and kinesins are similar becayse they:

1. walk toward the plus end
2. have 2 heavy chains and 2 light chains

dyneins

family of motor proteins that travel toward the minus end of microtubules and have 3 heavy chains and a variable number of light chains

function of cytoskeleton

holds organelles in place

motor proteins

mediate intracellular transport of vesicles

Arp1 filaments

actin-related proteins that act as intermediate elements in the attachment of dynein to the vesicle

myoblasts

muscle cell precursors that fuse to form huge multinucleated cells

myofibrils

makes up the cytoplasm of myoblasts and cylindrical and consists of sarcomeres

sarcomeres

contractile units that make up myofibrils and are composed of an ordered array of parallel, partly overlapping thin and thick filaments

thin filaments

composed of actin and associated proteins attached at the plus end to a Z disc, minus ends extend toward the center of the sarcomere (appear as light bands)

thick filaments

composed of myosin II bundles (dark bands)

During muscle contraction, what happens to actin and myosin filaments?

they slide past one another shortening the length of the sarcomere but not the filaments themselves

titin

large protein that holds thick myosin filaments in the center of the sarcomere

tropomodulin

caps actin filaments at the minus end

cap Z

caps actin filaments at the plus end

actin filaments are coated with ____________.

nebulin, tropomyosin, troponin

Muscle contraction is initiated by a sudden rise in _________.

cytosolic calcium

muscle contraction

sliding of myosin II molecular motors along actin filaments

cilia and flagella are highly specialized structures that mediate ___________.

cell movement

flagella

found on sperm cells and protozoa, propel the cell forward and undulating motion

cilia

found on surface of epithelial cells and on protozoa, beat with a whip-like motion in one direction and flow back to the original position

axoneme

precise microtubule organization arranged in 9+2 of flagella and cilia

A microtubules

whole microtubule filaments

B microtubules

partial microtubules

axonemal dyneins

large molecular motors attached to axonemal A microtubules that toward the minus end of B microtubules

What causes axoneme bending and flagellar motion

when axonemal dyneins walk towards the minus end

cell cycle

controls multiplication of cells

cell-cycle control system

complex network of regulatory proteins that governs progression through the cell cycle
- basis: DNA replication, segregation of replicated chromosomes

Mitosis (M) phase

prophase, metaphase, anaphase, telophase, cytokinesis

interphase/"non-splitting phase"

longest stage of cell division

Interphase phases

G1, S, G2

G1 and G2 (GAP) phases

cell grows and increases in volume, length of phase varies

S phase

cell duplicates its genome (DNA synthesis)

G0

special sate that cells enter when extracellular conditions are unfavorable

cell cycle control system

controls the cell cycle like an automatic washing machine