Cytoskeleton-MF

Question 1

Smallest cytoskeletal filament

Answer 1

Microfilament
Actin filament
F-actin

Question 2

MF are known for

Answer 2

Their role in muscle contraction

Question 3

Building blocks of MF is

Answer 3

Actin

Question 4

Actin is

Answer 4

Highly conserved globular protein

Question 5

Actin types

Answer 5

Alpha-actin: muscle specific actin
Betta-actin: apical
Gamma-actin: basal

Question 6

Most abundant in all eukaryotic cells

Answer 6

Actin

Question 7

Actin after synthesis

Answer 7

Folds into globular U-shaped molecule that can bind ATP or ADP

Question 8

G-actin (globular actin) will

Answer 8

Polymerize to form microfilaments (F-actin) filamentous actin

Question 9

MF hydrolyze —— but MT hydrolyze ——

Answer 9

ATP
GTP

Question 10

G actin can polymerize reversibly to

Answer 10

Filaments with lag phase, elongation phase

Question 11

F-actin

Answer 11

Composed of two linear strand of polymerized G-actin wound into helix

Question 12

All actin filament have——

Answer 12

Same orientation

Question 13

Actin filament

Answer 13

-two stranded helical polymer
-concentrated beneath the plasma membrane
-easily change cell morphology by assembling/disassembling (Dynamic)
-MF have polarity
-Requires ATP (actin is ATPase)

Question 14

Polarity of MF reflect on

Answer 14

More rapid addition of G-actin at + end than - end

Question 15

After G actin assembles onto MF,

Answer 15

ATP bound to them slowly hydrolyzed
hydrolysis is not required for polymerization

Question 16

Growing end has

Answer 16

ATP actin

Question 17

Most of Mf has

Answer 17

ADP actin

Question 18

Treadmilling can occur in

Answer 18

MT and MF

Question 19

Cells can regulate how MF are assembled such as

Answer 19

1- Cell that crawl: Lamellipodia and Filopodia at leading edge
2- cell that adhere tightly: stress fibers

Question 20

—— organize and behave the MFs

Answer 20

Actin binding proteins

Question 21

Actin binding proteins

Answer 21

1- ARP complex
2- Thymosin Betta 4
3- CapZ/ Tropomoduli
4- Formin
5- Cofilin
6- Filamin/ alpha-actinin
7- Gelsolin
8- Spectrin/Ankyrin

Question 22

Thymosin Betta-4

Answer 22

Bind to (+ end) ATP-actin monomer and prevent them from polymerization

Question 23

Profilin

Answer 23

Binds to ADP-G-actin catalyze the exchange ADP to ATP, promoting polymerization

Question 24

Cofilin

Answer 24

Bind (- end) ADP-actin in MF, severe it promote depolarization

Question 25

Capping proteins

Answer 25

CapZ: bind to + end, prevent addition/loss of subunit Tropomodulin: bind to - end, prevent addition/loss of subunit **physically binding**

Question 26

Sever actin filaments

Answer 26

Gelsolin: break actin MF and caps the newly exposed + end Cofilin: filament-severing proteins, facilitating depolarization

Question 27

Formins

Answer 27

Control the assembly of actin filament Nucleate polymerization of unbranched actin filament Associated with + end, enabling rapid insertion of actin filament and protect the end from capping proteins

Question 28

Some Formins have extensions that can bind

Answer 28

Profilin

Question 29

Cross link filaments

Answer 29

Filamin: join two MF together

Question 30

Bundle actin filament

Answer 30

Fimbrin: bundle Mf in microvilli

Question 31

Link MF to membrane

Answer 31

One or more peripheral membrane proteins: spectrin and Ankyrin

Question 32

Nucleate new filaments

Answer 32

Arp2/3 complex: nucleate new branches, tree-like network

Question 33

Intermediate filament

Answer 33

Are not polarized Support the cytoskeleton by acting as scaffold(bridging molecules) between Mt and MF

Question 34

Intermediate filament assemble from

Answer 34

Fibrous Subunits rather than globular

Question 35

Intermediate filament

Answer 35

-Central rod-shaped alpha-helix domain that is conserved -Has N-terminus and C-terminus that differ greatly -unlike MT and MF can be made of many different proteins -have only been found in animals - expression vary from tissue-to-tissue

Question 36

Intermediate filament classified based on

Answer 36

Degree of AA

Question 37

N terminus and c terminus sequence and structure can vary the most as they can binding site for

Answer 37

-intermediate filament -MF -MT

Question 38

—— can help in diagnosis of certain tumors

Answer 38

Intermediate filament

Question 39

Tumor cells

Answer 39

Lose morphological appearance but retain cytoskeletal proteins By using of antibodies against IF can determine if origin is epithelial, mesenchymal, neural

Question 40

IF proteins synthesize

Answer 40

-Primarily fibrous molecules, globular domain on each end -two polypeptide spontaneously interact, wrapping around each other, create dimer Two dimer assemble creating anti-parallel tetramer(no polarity) Eight tetramers pack laterally to form one unit Unit associate with each other to form elongated IF

Question 41

Unlike MF and MT, in IF,

Answer 41

Units are not removed from ends, rather the interior

Question 42

IF assembly does not

Answer 42

Require energy (ATP or GTP)

Question 43

IF mechanical strength

Answer 43

MT resist bending MF generate tension IF elastic and withstand tensile forces IF are most stable cytoskeleton component IF are not static, dynamically remodeled

Question 44

IF examples

Answer 44

Nuclear Matrix Nuclear Lamina Both supporting structures

Question 45

Nuclear matrix (nucleoskeleton)

Answer 45

Insoluble fibrous network Maintains the shape of nucleus Attachment site for chromatin

Question 46

Nuclear Lamina

Answer 46

Thin dense fibers lining the inner surface of inner nuclear membrane -made of IF composed of Lamina -disassemble prior to mitosis by phosphorylation of Lamins