Cell environment

Question 1

Actin filaments function

Answer 1

determine the shape of the cell, provide mechanical stiffness and allow cell movement and muscle contraction.

Question 2

Actin filaments structure

Answer 2

• individual filaments are 5-9 nm in diameter
• can be bundled together into thicker filaments which are much stronger than individual filaments.
• rigid, compared to the plasma membrane which is elastic and fluid.

Question 3

Which end does actin filament grow and how

Answer 3

Actin monomers join a growing filament at the plus end if they are bound to ATP.

Growth of actin filaments at the front of the cell (pink ends) push the plasma membrane forward. This piece of the membrane then attaches to the surface allowing the cell to pull itself forward.

Question 4

Actin

Answer 4

one of the most highly conserved proteins across species and makes up 1-5% of a typical cell by weight (20% in muscle)

Question 5

Cytoskeleton

Answer 5

• Actin filament
• Microtubules
• Intermediate filaments

Question 6

Microtubules function

Answer 6

• help position organelles,
• provide an internal transport system in cells
• essential for cell division.
• help shape the cell
• involved in cell movement.

Question 7

Microtubules structure

Answer 7

• larger than actin filaments with an outer diameter of 25nm.
• hollow cylinders
• much more rigid than actin filaments.
• All microtubules typically originate from a single point in the cell called the Microtubule Organising Centre.

Question 8

Which end does microtubule grow and how

Answer 8

Tubulin monomers (alpha and beta tubulin) bind to the plus end when bound to GTP.

Microtubules grow and shrink from the plus end, with the minus end usually anchored to the microtubule organising centre.

Question 9

Intermediate filaments structure

Answer 9

Intermediate filaments are more diverse than microtubules or actin filaments, composed of a wider range of proteins.

Rope-like fibres that are typically 8-12 nm in diameter

Dimer > Teramer> Protofilaments > Intermediate filament

Question 10

Intermediate filaments function

Answer 10

• Provide mechanical strength to the cell and are used to connect cells together in tissues
• Also form the nuclear lamina, just beneath the nuclear membrane that helps anchor chromosomes and the nuclear pore complex.

Question 11

The cytoskeleton of a cell is fixed T/F

Answer 11

False

The cytoskeleton of a cell is extremely dynamic and is constantly re-organising

Question 12

What happened to the actin filaments as the cell senses it’s environment?

Answer 12

Actin filaments extend and contract constantly, pushing out the plasma membrane as the cell senses it’s environment.

As cells move the entire actin network can be remodelled extremely rapidly.

Question 13

Microtubules are dynamic T/ F

Answer 13

True
Microtubules are also dynamic and remodel to allow the cell to send organelles or vesicles to new parts of the cell or during cell division when the mitotic spindle forms.

Question 14

A cell in telophase would undergo ________

Answer 14

cytokinesis- cleavage furrow (contractile ring of actin filaments) seperated the two daughter cells

Question 15

treadmilling

Answer 15

• The cell has a finite pool of actin monomers
• To keep growing actin filaments disassemble from the back (minus end) and re-assemble at the front (plus end). With G- actin, the actin monomers, adding onto the plus end of the F- actin, the body) and shrink at the minus end

Question 16

Microtubules exhibit dynamic instability because ?

How to stablise microtubules ?

Answer 16

Microtubules shrink about 100 times faster than they grow and therefore exhibit dynamic instability.

Cells cap the ends of microtubules to stabilise them.

Question 17

Steps in the migration cycle include -

Answer 17

• Protrusion
• Adhesion
• Retraction

Question 18

Cell migration is important in -

Answer 18

• cancer metastasis
• angiogenesis
• wound repair
• pregnancy
• embryo development
• immune response

Question 19

Re-organisation of the cytoskeleton is essential for

Answer 19

cells to be able to move

Question 20

the migration cycle steps are important in

Answer 20

in other biological processes such as platelet spreading, axonal projection and mechanosensing.

Question 21

chemotaxis

Answer 21

Cell migration

The dynamic nature of acting filaments and the rest of the cytoskeleton allows the cell to very rapidly change shape or its direction of movement in response to signals from the environment, such as nutrient source

Question 22

Interfering with the cytoskeleton has no effect to the cell. T/F

Answer 22

False

is usually extremely harmful to the cell.

Question 23

Many drugs and toxins are known to either _______ or _______ microtubules or actin filaments.

Drugs can target the _________. Some of these drugs are used to treat __________

Answer 23

either stabilise or destabilise

cytoskeleton / cancer and other diseases.

Question 24

Drugs that target the cytoskeleton

Answer 24

Check table on Lec 17- 18 Slide 20

Question 25

Joining the cytoskeleton of cells through actin filaments or ________ ___________ provides________ ______ to tissues.

Answer 25

intermediate filaments

mechanical strength

Question 26

Organising cells into epithelial tissues, mechanical stresses are

Answer 26

transmitted from cell to cell by cytoskeletal filaments anchored to cell- matrix and cell- cell adhesion sites

Question 27

Organising cells into connective tissues, mechanical stresses are

Answer 27

the mechanical stresses of compression and tension directly beared by extracellular matrix

Question 28

Joining the cytoskeleton of cells allow ______ action, such as in _______ and _______ muscle, where the actin filaments are _______ to allow ________ ______ __________

Answer 28

• co-ordinated action
• cardiac and skeletal muscle
• aligned (arrange in line to be parallel)
• allow efficient muscle contraction.

Question 29

In skeletal muscle the cells _____with each other to create _________. During fusion the actin filaments are ____________.

Answer 29

• fuse
• one long multi-nucleate cell
• aligned between cells