Ims: Histo Block 1 Lecture 3

Front 1

What roles does the cytoskeleton play in the cell?

Back 1

Spatial organization, polarity, morphogenesis
Provides framework for cell activities
Micortubules and actin fils provide track for motor proteins involved in intracell transport, motility, contractility

Front 2

How did intermediate fibers get their name?

Back 2

Intermediate in diameter when compared to actin and microfils

Front 3

What roles do intermediate fils play in the cell?

Back 3

Form network to reinforce and anchor cells to one another and to ECM
Help determine shape of many cells

Front 4

Describe role of the protein, plectin.

Back 4

cross-links IM fibers to each other, and to MT's, and to actin fils

Front 5

How is an intermediate fiber constructed?

Back 5

-Monomer with highly conserved central rod domain (alpha-helical) and varying globular heads at N and C-terminus
-2 monomers coil around each other to form dimer
-2 dimers of opp polarity stagger to form tetramer (noncovalent bonds holding together)
8 tetramers form IM fil (many noncovalent bonds)

Front 6

Provide cytoplasmic and nuclear examples of IM fils.

Back 6

Cyto: keratins (in epithelia), vimentin (in connective tissue, muscle, neuro), neurofils (nerve cells)

Nuclear: nuclear lamina (all animal cells)

Front 7

Describe the subatomic structure of microtubules.

Back 7

13 protofilaments comprised of tubulin heterodimers

Each dimer has alpha tubulin at minus end and beta tubulin at plus end, allowing for polarity

MT's form long, unbranched cylinders

Front 8

Describe the structure that allows for growth of microtubules. Provide an overview of the process.

Back 8

Known as Microtubule Organizing Center (MTOC):
A centrosome is a proteinaceous structure containing a pair of centrioles within it (play no role in MT growth) and has gamma-tubulin rings
Gamma tubulin rings nucleate microtubules
Plus end of the MT is away from the centrosome, minus end is at gamma-tubulin ring on centrosome
Dimers add at plus end of MT
GTP is required for MT growth

Front 9

How do MTOC's and MT's give rise to cell polarity?

Back 9

Centrosomes nucleate MT's in interphase cells and occur at poles of the mitotic cell
The polarity of the MT's and the position of the MTOC's provide polarity to the cell bc the centrosome occurs near the anterior of the migrating cell

Front 10

How are MT's affected by drugs that block tubulin dimer dissasembly? That block their assembly?

Back 10

Assembly occurs in absence of disassembly and vice versa.

Front 11

What general roles does actin play in the cell?

Back 11

Can form tight bundles in microvilli to provide support, can form loose networks in cortex (immediately below cell membrane),

Are involved in cell locomotion and cytokinesis

Muscle has highly ordered actin fils for sliding

Front 12

Describe the subatomic structure of actin.

Back 12

Globular monomers of actin (G-actin) join head-to-tail to form a polarized protofilament (plus and minus ends)

Two parallel protofils of actin with same polarity bind around each other to form a right-handed helix and thus become filamentous actin (F-actin)

Front 13

How do actin filaments compare to MT's?

Back 13

actin fils are more flexible and are often shorter than MT's

Front 14

Describe the assembly and disassembly of actin filaments.

Back 14

New actin filaments are nucleated by actin-related protein complexes (ARP)

Actin monomers + ATP can join either end, but it's faster at plus end

ATP is hydrolyzed after incorporation, which makes filament less stable, promoting filament disassembly at other end

Front 15

In what processes are actin polyermization and depolymerization necessary?

Back 15

motor molecule myosin, cell ameboid movement

Front 16

Describe the role of thymosin.

Back 16

Thymosin is a monomer-sequestering protein, it sequesters actin monomers in cytosol so there isn't extensive polymerization of filaments

Front 17

Describe the role of gelsolin.

Back 17

It's a severing protein. It fragments actin-fils.

Front 18

Describe the role of capping proteins.

Back 18

Capping proteins prevent assembly and disassembly of actin fils

Front 19

Describe the role of nucleating proteins.

Back 19

Promote assembly of actin fils.

Front 20

Describe the role of myosin-I in vesicle transport. What does this require?

Back 20

All myosin molecules, except one, move along F-actin towards plus end

Myosin-I tail attaches to vesicle which will be moved along actin-filament to plus end by muyosin head hydrolyzing ATP

Requires ATP to bind, detach, and rebind myosin to actin

Front 21

How could an actin filament be transported along a cell membrane?

Back 21

myosin-I binds cell membrane, moves actin-filament over (along) it

Front 22

Describe the role of myosin-II in actin filaments and overall cell function.

Back 22

Head of myosin-II "walks" along actin towards plus end
Myosin-II is a bipolar filament, so two head domains move toward each other (each head bound to parallel strand of actin)
Thus distance is shortened between plus ends of actin filaments (SLIDING)
This occurs in muscle, and it contractile bundles during cytokinesis

Front 23

How are motor molecules able to "walk" along microtubules? Provide specific names.

Back 23

Motor molecules use hydrolysis of ATP on their head regions (bound to MT's) to conformationally change and walk along MT

Kinesin moves to plus end
Dynein moves to minus end

Front 24

How do motor molecules carry cargo?

Back 24

Tail of motor molecule binds organelle or vesicle (different tail according to cargo carried), kinesin and dynein can move cargo in oppo directions

Cargo can shift from actin fils to MTs and vice versa

Front 25

Contrast cilia with flagella.

Back 25

Flagella occur in small numbers (1 per sperm), cilia occur in large numbers and move in waves where beat of each cilium is slightly out of phase.

Cilia can move liquid over surfaces (like mucus in respiratory tract)

Front 26

How is ciliary bending achieved?

Back 26

In an isolated doublet of microtubules, dynein would produce sliding. So if you use linkage proteins (nexinand radial spokes) convert the sliding into a bending motio.

Front 27

What would the respiratory effects be if a person lacked dynein arms?

Back 27

Wouldn't be able to clear mucus from respiratory tract!

Front 28

What's a primary cilia? Function?

Back 28

SHort structures sans dynein; don't move

Some have signaling proteins and play roles in development, flow sensors in kidneys