Cytoskeleton lec 1 (lecture 10)

Question 1

Describe the cytoskeleton on whether you think it is dynamic?

Answer 1

SOME!!: highly dynamic

Question 2

10 functions of the cytoskeleton?

Answer 2

• mitosis
• cytokinesis
• traffic (diffusion of protein is not random
  )- Sperm to swim (flagella: eus and pro different (structure))
• White blood cells to crawl (
• Muscle contraction
• Formation of axons/dendrites
• Cell shape
• Growth of plant

Question 3

Three types of cytoskeleton (and their diameters)

Answer 3

• Intermediate filaments (10nm)
• Microtubules (20nm diameter (large))
• Actin filaments (7nm) – smaller

Question 4

Stability of intermediate filaments

Answer 4

STABLE, rarely undergo rearrangement

Question 5

Function of the intermediate filaments, abundance where?

Answer 5

add strength to cells, therefore abundant in cells which require mechanical strength eg skin cells

Question 6

Where else do we find intermediate filaments other than the cytoplasm

Answer 6

nucleus, neurofilaments

Question 7

How do intermediate filaments arrange themselves (generally)

Answer 7

monomers, which self associate to form multimeric structures

Question 8

Keratin?

Answer 8

type of intermediate filament found in epithelial cells

Question 9

Vimentin ?

Answer 9

type of intermediate filament found in connective and nerve tissue

Question 10

Intermediate have what type of termini ? And between?

Answer 10

Globular N and C termini with a long alpha helical stretch of non polar amino acids

Question 11

Average length of an individual intermediate filament?

Answer 11

48nm

Question 12

coiled-coil Dimers of intermediate filaments are formed when?

Answer 12

Two monomers of intermediate filament protein associate to form a dimer by coiling their alpha helices around each other

Question 13

Staggered tetramers are formed by?

Answer 13

Two dimers lining up

antiparallel n >c C>N

Question 14

How to tetramers interact ?

Answer 14

N-termini of the monomers (in one dimer) interact with the C-termini of adjacent monomers (in another dimer).

Question 15

Rope like structures of intermediate filaments are formed when?

Answer 15

Eight tetramers are twisted into a rope of diameter approx 10 nm

Question 16

‘Cell junctions’ cause interaction between cells by?

Answer 16

Indirectly connected to filaments of other cells through cell-cell junctions called desmosomes to neighbouring cells

Question 17

Cadherins function ?

Answer 17

span the two
membranes and bind the 2
cells together

Question 18

Cadherins interact with?

Answer 18

Plaque proteins on the cytosolic side of membranes

Question 19

Plaque proteins interact with?

Answer 19

The plaque proteins interact with keratin filaments

Question 20

Order of interactions between cells and different molecules from one cell to another?

Answer 20

Keratin to plaque to cadherin (in and inside the membrane of both cells) to plaque to keratin

HENCE INDIRECTLY

Question 21

Example of an Intermediate filament disorder?

what type of disorder

effects?

Answer 21

Epidermolysis bullosa simplex

rare, recessive

Keratin cannot form normal filaments in the skin, prone to mechanical injury

Question 22

Nuclear lamina, purpose ?

Answer 22

a network of intermediate filaments beneath the nuclear membrane

Give the nucleus its shape

Question 23

Laminins are what type of proteins?

Answer 23

Extracellular matrix proteins, NOT CYTOSKELETAL proteins

Question 24

When cells are treated with salt or ionic detergent?- iNTERMEDIATE FILAMENTS

Answer 24

They remain largely in tact

Question 25

Actin abundance

Answer 25

very

Question 26

Where is actin found

Answer 26

all eu cells

Question 27

Actin Filaments made up of?

Answer 27

small globular proteins, nearly end to end

Question 28

Stability of actin

Answer 28

- Usually unstable

Question 29

Dynamic nature of actin filaments

Answer 29

DYNAMIC

Question 30

Free actin?

Answer 30

G- actin

Question 31

When G-actin associates

Answer 31

f- actin

Question 32

Experiment with G and F actin?

Answer 32

Take actin monomer and have them in vitro, put g atin in a test tube, add ATP, salt, mg, k, g actin will spontaneously begin to form filaments (F-Actin) (as long as conc of actin is high enough)

Question 33

Critical concentration?

Answer 33

Concentration of G-actin needed to polymerise spontaneously

Question 34

Why in vivo does actin reach a maximum of polymerisation?

Answer 34

``` Polymerisation is balanceed with depolymerisation still changing (dynamic) but chain length is not increasing ```

Question 35

Polarity of acton filaments?

Answer 35

POLARITY NOT DUE TO ELECTRICAL CHARGE - Globular - 2 lobes - Minus end (ATP binding clef exposed) - Plus end (dome of actin exposed)

Question 36

proteins which bind to actin to modify its properties (6)

Answer 36

``` Monomer binding proteins Nucleating proteins Cross linking proteins Capping proteins Bundling proteins Motor proteins ```

Question 37

Motor proteins function ?

Answer 37

Associates with actin, moves along filaments (have directionality)

Question 38

Nucleating proteins function?

Answer 38

actin filaments at membranes | determines where assemble happens

Question 39

Describe the function of the drug Cytoclasin D?

Answer 39

binds to the +ve end of F-ACTIN, prevenst further addition at + end

Question 40

Phalloidin drug function?

Answer 40

mushroom, binds to F-actin and prevents actin filaments from depolymerising, stabilises, stops cells from crawling

Question 41

Functions of actin

Answer 41

Mechanical strength and cell shape Cell crawling Muscle contraction Organelle movement

Question 42

Where are actin filaments concentrated?

Answer 42

are usually concentrated in a layer just below the plasma membrane (cortex)

Question 43

Actin binding proteins function?

Answer 43

Actin binding proteins link actin filaments into a meshwork

Question 44

Actin filaments provide what characteristic to cells?

Answer 44

Provide mechanical strength and cell shape

Question 45

Filipodia

Answer 45

are finger/needle like projections of the plasma membrane

Question 46

Lammelipodia

Answer 46

are sheet like projections of the plasma membrane

Question 47

Intergrins function within cell crawling?

Answer 47

Integrins (filopodia and lammelipodia) adhere to extracellular matrix, cells use internal contractions to pull itself forward

Question 48

Cell crawling is controlled by

Answer 48

rho and rac gtpases