lecture 9 - cytoskeleton

Question 1

What is the cytoskeleton?

Answer 1

• Network of protein filaments throughout the cytoplasm
• Important for supporting a large volume of cytosol
• Highly dynamic
• Responsible for cell shape and movement

Question 2

What are the functions the cytoskeleton?

Answer 2

• Mitosis
• Cytokinesis
• Traffick
• Support
• Sperm to swim
• White blood cells to crawl
• Muscle contraction
• Formation of axons/dendrites
• Cell shape
• Growth of plant cell wall

Question 3

what are the 3 types of cytoskeletal filament?

Answer 3

• Intermediate filaments (10 nm)
• Microtubules (25 nm)
• Actin filaments (7 nm)

Question 4

What do intermediate filaments do?

Answer 4

• approx 10 nm in diameter
• provide tensile strength
• abundant in cells that are subject to mechanical stress such as muscle, epithelial cells

Question 5

How are intermediate filaments grouped?

Answer 5

• Keratin filaments in epithelial cells
• Vimentin related filaments in connective tissues , muscles and nervous tissues
• Neurofilaments

Question 6

How are intermediates constructed?

Answer 6

• made up of monomers with central rod and a globular region at either end
• they must dimerise

Question 7

What does a intermediate filament look like?

Answer 7

• helices coil around each other, this is called a coiled coil dimer
• two dimer line up in a staggered tetramer
• opposite ends, N terminus to C terminus
• no polarity
• form tetramers

Question 8

What are keratins?

Answer 8

• span the interior of the epithelial cells from one side to the other
• indirectly connected to filaments of other cells through cell to cell junctions called desmosomes

Question 9

How are desmosomes formatted?

Answer 9

There is a keratin filaments attached to a plaque protein, the plaque protein is also attached to cadherins which span the membrane

Question 10

What do cadherins do?

Answer 10

span the two membranes and bind two cells together

Question 11

What do plaque proteins do?

Answer 11

They are attached to integral membrane proteins

Question 12

What do keratin filaments do?

Answer 12

anchored to the cytoplasmic plaque

Question 13

What is a intermediate filament disorder?

Answer 13

• epidermolysis bulls simplex
• rare genetic disorder
• keratin cannot form normal filaments in the epidermis
• skin is highly susceptible to mechanical injury

Question 14

What is the nuclear lamina?

Answer 14

The network under the nucleus which gives it is strength

Question 15

Where are Actin filaments found?

Answer 15

in all eukaryotic cells

Question 16

A description of actin filaments

Answer 16

• diameter of 7nm and are the smallest of the 3 types of filaments
• made up of globular monomers that associate head to tail
• the filaments are unstable without associated proteins

Question 17

What is G- actin ?

Answer 17

The monomer on its own

Question 18

What is F - actin?

Answer 18

When G - actins form polymers

Question 19

How is actin polymerised?

Answer 19

Actin monomers in the cytosol carry ATP
The ATP is hydrolysed to ADP soon after assembly into filament. The ADP bound monomer is less stable in the filament
The ADP cannot be exchanged for ATP until the monomer disassembles

Question 20

Why does an actin filament get to a stage when it doesn’t elongate anymore?

Answer 20

• rate of addition is the same as the rate of removal

- not growing but it is changing

Question 21

Which filaments have polarity?

Answer 21

• Actin

Intermediate filaments do not,

Question 22

What proteins bind to actin to modify its properties?

Answer 22

• monomer binding proteins
• nucleating proteins
• cross linking proteins
• capping proteins
• bundling proteins
• motor proteins , move along actin filaments, move from minus end to the plus end of the microfilament

Question 23

What does Cytochalasin D do in the cell?

Answer 23

• binds to the positive end of the F -actin and prevents further addition of - actin

Question 24

What does Phalliodin do in the cell?

Answer 24

• binds o F - actin and prevents actin filaments from depolymerising

Question 25

What are the overall functions of actin?

Answer 25

Mechanical strength and cell shape
Cell crawling
Muscle contraction
Organelle movement

Question 26

How do cells ‘crawl’?

Answer 26

Extensions called filopodia or lammelipodia extend a region of plasma membrane.
Integrins adhere to extracellular matrix
Cells use internal contractions to pull itself forward