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CellBio 2
cytoskeleton
88
Biology
Undergraduate 4
04/04/2008

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Term
what is the cytoskeleton
Definition
intricate network of protein filaments that extend throughout the cytoplasm
Term
what are the 3 main components of the cytoskeleton
Definition

intermediate filaments

actin filaments

microtubule filaments

Term
what holds together the subunits of the cytoskeleton
Definition

non-covalent bonds

hydrophobic interactions

Term
what are the 4 functions of the cytoskeletn
Definition

support cellular cytoplasm

intracellular transport

cell shape

motility

Term
which type cytoskeltal filament is twisted like a cable
Definition
intermediate filaments
Term
where are the 2 main locations where intermediate filaments are found
Definition

nuclear lamina

surrounding nucleus and extending to cell periphery

Term
which types of cells would be high in intermediate filaments
Definition

any that stretch (intermediate filaments have

high tensile strength)

muscle, GI, epithelial, etc

Term
what are the 2 types of actin subunits? what is the difference?
Definition

G actin - 'free' actin, globular, not in a filament

F actin - 'filamentous actin', assembled in filaments

Term
which type of actin subunit is bound to ATP
Definition
F actin
Term
what is the plus end of an actin filament?
Definition
the end that is assembled and disassembled quickly
Term
what are 3 main actin functions
Definition

muscle contraction

cleavage furrow formation

cell movement

Term
what are microvilli
Definition
fingerlike projections of a cell formed by actin arrangement
Term
where is actin located in a cell?
Definition
dispersed throughout cytoplasm but most concentrated in cortex
Term
what is the cortex. what are its main roles?
Definition

the layer of cytoplasm just beneath the plasma membrane.  high in actin concentration

1) maintain cell shape

2) help in formation of cell surface extensions (ex microvilli)

Term
what is the general structure of microtubules?
Definition
long, hollow cyliders
Term
what protein are microtubules made of?
Definition
tubulin
Term
which cytoskeletal protein is a heterodimer
Definition
tubulin (alpha and beta)
Term
which tubulin protein is always GTP bound (does not bind GDP)
Definition
alpha tubulin
Term
what are protofilaments?
Definition

tubulin dimers bound together in chains that make up microtubule walls

Term
what are the 4 main microtubule functions
Definition

intracellular transport

anchoring intracellular organelles

form mitotic spindle

csome separation during cell division

Term
what is a centrosome
Definition

the microtubule organizing center

Term
what is meant by dynamic instability
Definition
rapid interconversion between growing and shrinking state
Term
what is catastrophe
Definition
when an elongating microtubule shifts rapidly to shrinking
Term
what is rescur
Definition
when a shortening microtubuleshifts rapidly to elongation
Term
whhich type of cells have microtubules that are not dynamic?
Definition
neurons, axons packed w microtubules
Term
explain how microtubules find a cellular target
Definition
dynamic instability - grow in one direction, if they don't find something they disassemble and try again
Term
what is the general name of proteins that bind to microtubules
Definition

microtubule associated proteins (MAPs)

Term
what are the two main functions of MAPs
Definition

microtubule stability

motor function

Term
what are the two main motor MAPs? what is the main difference
Definition

kinesin - moves toward + end

dynein - moves toward - end

Term
what are the three main parts of a motor MAP
Definition

motor head

cargo

tail

Term
what MAP associated with muscle contraction
Definition
myosin II
Term
what are mysoin proteins
Definition
a family of similar proteins that bind to actin filaments and hydolyze ATP to move in the + direction
Term
explain the structure of a myosin molecule
Definition

head domain/motor domain = 2 light chains

tail domain = 2 heavy chains, twisted together

Term
what does the sliding filament model explain?
Definition

muscle movement in vertebrates.

myosin molecules connect actin filaments, move in opp directions to pull filaments together.

myosin fibers along a sarcomere 'walk' along adjacent actin strands, pulling the 'z line' together

Term
what is a sarcomere. what are 2 main connecting strands
Definition

a functional unit of skeletal muscle.

thick filaments (mostly myosin)

thin filaments (mostly actin)

Term
explain role of ATP in myosin movement
Definition

ATP attached to mysoin

1. hydrolysis to ADP causes conformationaly change to head region allowing it to bind actin

2. when ATP binds actin-bound myosin head get release from actin

3. repeat

Term
how is calcium involved in muscle contraction
Definition

when Ca is absent: tropomysin/tropin complex inhibits binding of actin and myosin

when Ca present: tropomysin/tropin complex released, allows movement 

Term
where is the calcium needed to initiate muscle movement stored in cells
Definition
in the sarcoplasmic reticulum (special type of smooth ER)
Term
summarize muscle contracton from impulse to contraction.
Definition

1. neurotransmitter triggeres surface receptor on cell

2. sarcoplasmic reticulum releases Ca

3. Ca causes tropomysin/tropin complex to release from actin

4. ATP-ADP causes myosin to bind actin

5. ADP-ATP causes mysoin to release actin

6. Adjacent actin filaments pulled together

Term
what role does actin play in the formation of a cleavage furrown
Definition
actin filaments make a ring around cell that 'cinches' together for cytokinesis
Term
what protein involved in contractile ring 'cinching'
Definition
myosin II
Term
when is the contractile ring formed
Definition
early anaphase
Term
how are microtubules involved in cytokinesis of animal cells
Definition
carry vessicles (via motor proteins) containing phospholipids and proteins needed to form new cell membrane
Term
explain cytokinesis in plant cells in regards to cytoskeletal components
Definition

early Anaphase - small vessicles containing polysaccharides and glycoproteins needed to form cell wall travel from Golgi on microtubules via motor proteins and align along equatorial region of the spindle

 

Term
what are some examples of cells that move by protruding cytoplasm
Definition
stem cells, macrophages, sex cells, fibroblases, amoeba
Term
what are the 3 main events of cell locomotion through cytoplasm extension
Definition

protrusion

adhesion

contraction

Term
what is the protrusion of cytoplasm used for cell movement called. how is this formed
Definition

lamellipodium.

myosin I pushes + end actin filaments against plasma membrane

Term
what proteins involved in the adhesion step of cell locomotion. what are they connected to
Definition

integrins.

intracellular domain - connected to actin filaments

extracellular domain - connected to ECM

Term
what happens in the contraction step of cell locomotion. what protein may be involved
Definition

back of cell contracts, pushing rest forward.

myosin II may be involved

Term
what is the structure of kinesin and dynein. how diff from mysoin? what drives movement? how diff functionally
Definition

head - 2 globular heavy chains

tail - 2 light chains, twisted

(mysoin has light head, heavy tail)

ATP driven

kinesin - + end directed

dynein - - end directed

Term
what drives microtubule movement? which microtubules are + directed
Definition

ATP

kinesisn + myosin I/II = plus end directed

dynein = neg end

Term
which MAP involved in csome attachemnt? separation?
Definition

kinesin - attachment (+ end)

dynein - separation (- end)

Term
what is the kinetochore
Definition
complex of proteins + RNA that attach to centromere. link csome and spindle fiber
Term
what are 3 classifications of microtubules in cell division
Definition

astral microtubules -face csome side of centrosome

polar microtubules - face pm side of centrosome

kinetochore microtubule - astral mctble that is attached to csome

Term
how doea csome separtation occur
Definition
tubulin subunits taken off of both ends of microtubule (kintetochore end and centrosome end)
Term
which protein associated w centrosome end of microtubule? kinetochore end?
Definition

centrosome end (-) - kinesin

kinetochore end (+) - dynein

Term
how do csomes align during metaphase?
Definition
Term
what are growth factors? how linked to cancer
Definition

extracellular signal proteins that bind surface receptors and cause intracellular signaling resulting in expression of genes needed for cell division

- in some cancer, growth factors are continually bound to their recpetors

Term
what is a main checkpoint involved in monitoring DNA replication
Definition
S/G2 checkpoint
Term
what are the 4 stages of the cell cycle
Definition

S

G2

M

G1

Term
what is metastasis. how does it ocur
Definition

migration of cancer cells.

1) adhesion to neighboring cells broken

2) migration via actin filaments to other parts of the body

Term
what are 2 cancer drugs that target MTs? how diff
Definition

Vinblastine - binds MTs, causes disassembly

Taxol - binds MTs, prevents disassembly

Term
other than cancer, what other disease have MTs been implicated in
Definition
Alzheimer's, Parkinsons - axon MTs should be fixed, may be collapsing in these disease
Term
how do proteins synthesized in cell find target in cytoplasm
Definition
localization signals - small aa sequences that are specific to destination
Term
what is the nuclear envelope
Definition
double nuclear membrane containing nuclear pore complex
Term
what is the basic structure of a nuclear pore
Definition

octagonal structure of repeating subunits

called nucleoporins with fibrils extending into cytoplasm and nycleus making up the nuclear cage

Term
what is the nuclear cage
Definition
fibrils associated w nuclear pore that extend into nucleus and into cytoplasm
Term
what types of molecules are transported into the nuc? out?
Definition

in = histones, nucleotides, helicase, transcription and replication enzymes

out = mRNA, ribosomes

Term
what is facilitated diffusion
Definition
movement across a membrane through a channel
Term
how do small molecules such as water and ions travel across nuc membrane
Definition
facilitated diffusion
Term
explain transport of large molecules across nuc membrane
Definition

1. beta importin binds alpha importin to form active transport protein

2. transport protein binds adaptor proteins attached to nuc localization signal on molecule.

3. importins bind FG repeats on nucleoporins

4. GTP associated w pore is cleaved changing pore shape and allowing transport across memb.

5. importins released

Term
what is the benefit of adaptor proteins
Definition
allow importins to bind many diff nuc localization signals.
Term
explain nuclear export
Definition

1. molecules have nuclear export signals

2. export signals bind nuc export receptors (soluble proteins)

3. export receptors bind nucleoporin

4. GTP cleaved to open pore

5. transported across

Term
what are the 2 types of ribosomes
Definition
free and ER bound
Term
explain how proteins transported into ER
Definition

1. cytosollic (free) ribosome begins translation of mRNA

2. ER signal sequence on protein directs ribosome to ER

3. Signal recognition particle releases from ER, attaches to signal sequence

4. Translation is paused

5. SRP binds SRP receptor on ER surface

6. SRP releases, returns to ER membrane, translation resumes

7.  Peptide threaded through protein translocator/Sec61 pore protein

Term
what does cotranslational transport mean
Definition
tansport occurs as protein is being made (ex ER transport)
Term
what is the structure of SRP. what allows it to bind to many proteins
Definition

6 polypeptides w an RNA.

has pocket of methionines (flexible, multi-binding)

Term
what enzyme cleaves a soluble protein after it is threaded into the ER? what portion left in membrane?
Definition

signal peptidase enzyme

signal sequence left in membrane

Term
what sequence associated with a single pass TM protein?
Definition
stop transfer signal
Term
what is unique about a multi-pass TM protein?
Definition
signal sequence is in the middle of the polypeptide
Term
why are chaperones needed in the lumen of the ER?
Definition
because proteins threaded in need to be refolded to be active
Term
what are 2 types of chaperone proteins
Definition

binding proteins

heat shock proteins

Term
what are 2 ways that a chaperone protein can work
Definition

protect protein from misfolding

lower energy

Term
what is one way a chaperone can protect a protein from misfolding
Definition
forming a larger aggregate that prevents degradation
Term
how can a chaperone lower energy required for a protein to fold?
Definition
add side chains and/or cause conformational change that lowers E required
Term
explain how protein import occurs in mitochondria and chloroplasts
Definition

protein synthesized on cytosollic ribosomes

signal sequence casues migration to organelle

protein imported

signal peptidase cleaves protein

(post translational import)

Term
explain an example of the symbiotic nature of mitochondria and nucleus
Definition
many transcription factors needed to activate mitochondrial/chloroplast DNA produced by nucleus
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