The cytoskeleton

Question 1

what is the function of a skeleton?

Answer 1

function- allows the cell to keep its shape and modifies the shape due a response to environmental cues. Also controls intracellular movement of organelles

Question 2

what are the general features of a cytoskeleton?

Answer 2

The cytoskeleton is a complex network made of 3 different polymers:

-microtubules
-intermediate filaments
-actin filaments.

Question 3

What is the function of the polymer microtubules?

Answer 3

microtubules:
-organelle positioning
-intracellular transport

Question 4

what is the function of the polymer intermediate filaments

Answer 4

intermediate filaments:
-mechanical strength

Question 5

what is the function of actin filaments?

Answer 5

actin filaments:
-cell shape
-organelle shape
-cell migration

Question 6

definition of accessory proteins

Answer 6

accessory proteins- assist in the function of other proteins

Question 7

what do accessory proteins regulate?

Answer 7

accessory proteins regulate:
-site and rate of filament formation
-polymerisation/depolymerisation
-function

Question 8

what is the structure and function of microfilaments/actin filaments?

Answer 8

Structure:
-helical polymers made of ACTIN
-flexible, organised into 2D networks and 3D gels

Function:
-cell shape
-organelle shape
-cell migration

Question 9

what is the structure and function of intermediate filaments?

Answer 9

structure:
-heterogenous group of filamentous proteins (different types of proteins that forms filaments)
-rope like structure

function:
-gives mechanical strength to the cell

Question 10

what is the structure and function of microtubules?

Answer 10

structure:
-hollow tubes made of TUBULIN
-rigid, long straight

function:
-organelle positioning
-intracellular transport
-cell movement

Question 11

what is the structure of Actin filaments?

Answer 11

Actin filaments:
-twisted chains of monomers of the protein actin (G-actin) this chaoin constitutes the filamentous form of F-actin
-thinnest class of cytoskeleton filaments
-presents structural polarity
-associated with a large number of actin binding proteins

Question 12

How are F-actin filaments formed?

Answer 12

F-actin can grow by addition of actin monomers (G-actin) at either end

Question 13

what is the length o the filament determined by?

Answer 13

The length of the filament is determined by:
-concentration of G-actin
-presence of Actin Binding proteins

Question 14

What are G-actin levels controlled by?

Answer 14

G-actin levels are controlled mainly by 2 ABPs:

-Profillin- facilitates actin polymerization
-Thymosin b4- prevents the addition of actin monomers to F-actin

Question 15

What is the role of Actin Bundling proteins and Cross-linking proteins?

Answer 15

Actin Bundling Proteins- Keeps F-actin in parallel bundles (as the microvilli observed in epithelial cells)

Cross linking proteins- maintains F-actin in a gel like meshwork

Question 16

What is the role of F-actin severing proteins and Motor proteins (Myosin)?

Answer 16

F-actin severing proteins:
-break F-actin into smaller filaments

Motor proteins (Myosin):
-transport of vesicles and/or organelles through actin filaments

Question 17

Describe the structure and function of skeletal muscle?

Answer 17

structure:
-arranged in a para-crystalline array integrated with different ABPs

function- interaction with myosin motors allow muscles to contract

Question 18

describe the structure of non muscle cells

Answer 18

structure:
-cell cortex: forms thin sheath beneath the plasma membrane
-associated with myosin to form a purse string ring.

Question 19

explain cell migration in the actin filaments

Answer 19

-the cell pushes out protrustions at its front.
-actin polymerisation
-these protrustions adhere to the surface
-integrins (link the actin filaments to the extracellular matrix)

Question 20

describe the structure of intermediate filaments (IF) ?

Answer 20

intermediate filaments:
-toughest of the cytoskeleton filaments
-ropelike with many long strands twisted together
-intermediate size (8-12nm)
-forms a network

Question 21

what is each unit of immediate filaments made of?

Answer 21

each unit is made of:
-N-terminal globular head
-C-terminal globular tail
-Central elongated rod-like domain

Question 22

What are 2 types of intermediate filaments?

Answer 22

1) Cytoplasmic
2) nuclear

Question 23

what does a nuclear intermediate filament form?

Answer 23

nuclear intermediate filaments:

-nucleur lamins in all nucleated cells

Question 23

what do cytoplasmic intermediate filaments form?

Answer 23

cytoplasmic intermediate filaments form:

-keratins in epithelia
-vimentin and vimentin-related in connective tissue, muscle cells and neuroglial cells
-neurofilaments in nerve cells

Question 24

explain the role of intermediate filaments binding proteins (IFBP)

Answer 24

IFBP stabilizes and reinforces IF into 3D networks

Question 25

list examples of IFBP

Answer 25

Examples IFBP:
-Fillagrin:
binds keratin filaments into bundles

-Synamin and Plectin:
binds desmin and vimentin
-link IF to the other cytoskeleton compounds

Plakins:

Question 26

what is the function of the IF in the cytoplasm?

Answer 26

IF- tensile strength: this enables the cell to withstand mechanical stress so they can stretch

Question 27

what are the functions of the intermediate filaments in the nucleus?

Answer 27

functions of intermediate filaments in the nucleus:
-present in all nucleated eukaryotic cells
-forms mesh rather than rope-like structure
-line in the inner face of nuclear envelope allows it to strengthen and provide attachment sites for chromatin
-disassemble and reform at each cell division as nuclear envelope

Question 28

what is the structure of microtubules?

Answer 28

structure of microtubules:
-hollow tubes made up of the protein tubulin
-relatively stiff (25nm)
-each filament is polarised
-assemble/disassemble in response to the cells needs

Question 29

definition of microtubule organising centre (MTOC)

Answer 29

MTOC- specialised protein complexes from where the assembly of tubulin starts

Question 30

what are the functions of microtubules?

Answer 30

INTRACELLULAR TRANSPORT:
-act like railway tracks on which molecular motors run
-different motors for different cargoes
-directionality of filaments is vital

ORGANISES POSITION OF ORGANELLES:
-provides polarisation of cells
-directionality of filaments is vital