Cell mobility: microtubules + actin microfilaments

Question 1

What do cells need to be able to move?

Answer 1

-energy
-guidance
-mechanical interaction with something outside the cell

Question 2

What are the 2 possible ways of moving through 3 dimensions and how?

Answer 2

-swimming - microtubules
-crawling - actin microfilaments

Question 3

What are the 2 types of cargoes in microtubule-based motility?

Answer 3

-cargoes of cells - the cell is what moves e.g sperm
-cargoes of fluids - cell stays in place + the surroundings move e.g respiratory tract

Question 4

Describe the structure of microtubules

Answer 4

-hollow tubes to provide strength
-made of alpha + beta tubulin
-has 13 protofilaments side by side, which is a conserved structure

Question 5

What is the difference in structure between cilia and flagella, and what major functional structure do they both have?

Answer 5

-same structure
-different lengths - flagella are longer
-both have the Axoneme

Question 6

Describe the structure of the axoneme

Answer 6

-9 outer doublets (microtubules) form a ring
-has an inner pair of microtubules
-radial spokes hold the axoneme together

Question 7

Describe the outer doublets of the axoneme

Answer 7

-made of complete A fibres (13 protofilaments) and incomplete B fibres (10 protofilaments)
-have inner + outer dynein arms - motor proteins that work with microtubules to introduce motion

Question 8

Why is there polarity across the axoneme?

Answer 8

There’s contact on one side and none on the other

Question 9

How does sliding occur with dynein?

Answer 9

-dynein tightly bound onto 1 microtubule but can bind to adjacent one
-allows movement between tubules
-2 doublets are connected by dynein arms
-apply ATP + doublets slide past each other

Question 10

What changes are made to achieve flexion instead of sliding?

Answer 10

Add a nexin crosslink between 2 doublets to act as an anchor

Question 11

What are the differences in wave forms between flagella and cilia?

Answer 11

-flagella have a wave like stroke
-cilia have a power stroke followed by recovery stroke

Question 12

What does the wave form that occurs depend on?

Answer 12

-the dynein molecules
-outer arm provides power
-inner arm controls waveform

Question 13

What is the transition zone?

Answer 13

Where the axoneme joins to what inside the cell (basal body)

Question 14

What is the basal body and what’s its structure like?

Answer 14

-anchor point in cell to connect the flagella to cytoskeleton of cell
-similar to axoneme but missing inner pair
-9x3 microtubule array - triplets instead of doublets

Question 15

Describe the structure of an actin filament

Answer 15

-+ive end and -ive end - polarity along the length
-ATP embedded in centre - hydrolysis as molecule polymerises, driving formation of a fibre

Question 16

Describe the finer structure of a microtubule

Answer 16

-has GTP/GDP in centre of each monomer (alpha/beta tubulin) - hydrolysed during polymerisation to act as energy source
-+ive and -ive ends - polarity along the length
-+ive end where we see polymerisation
–ive end stays same or gets broken apart
-actin is added at +ive end and lost at -ive end

Question 17

What is the filament and motor for cilia/flagella and the cytoskeleton/muscle?

Answer 17

-cilia/flagella: filament = microtubule, motor = dynein
-cytoskeleton/muscle: filament = actin, motor = myosin

Question 18

Describe the structure of myosin

Answer 18

-coiled coil of 2 alpha helices
-has a C-terminus + N-terminus (this is the ‘head’)
-neck or hinge region between chain and N-terminus

Question 19

What are the components involved in actin-based motility?

Answer 19

-filopodium - small projections that’re flexible for cells to reach out a short distance to test their environment
-lamellipodium - meshwork of filaments that move the whole front of the cell forward
-stress fibres inside cell pill the cell along by forming parallel bundles
-cortical actin - sheath surrounding the cell responsible for the mechanism of migration