3.3 Cytoskeleton

Question 1

What is the cytoskeleton?

Answer 1

contains actin filaments, intermediate filaments, and microtubules, which maintains cell shape and allows its parts to move

Question 2

How is the cytoskeleton structured?

Answer 2

the protein components interconnect and extend from the nucleus to the plasma membrane in eukaryotic

Question 3

What is the cytoskeleton often compared to?

Answer 3

the bones and muscles of an animal

Question 4

Why is the cytoskeleton dynamic?

Answer 4

because its protein components can assemble and disassemble as needed

Question 5

What are actin filaments?

Answer 5

long, extremely thin, flexible fibres that occur in bundles or meshlike networks

Question 6

What does each actin filament contain?

Answer 6

2 chains of globular actin monomers twisted about one another in a helical manner

Question 7

What is the role of actin filaments?

Answer 7

they play a structural role when they form a dense, complex web just under the plasma membrane, to which they are anchored by special proteins

Question 8

Where are actin filaments also seen?

Answer 8

in the microvilli that project from intestinal cells, and their presence accounts for the formation of pseudopods

Question 9

What are pseudopods (false feet)?

Answer 9

extensions that allow certain cells to move in an amoeboid fashion

Question 10

How do actin filaments produce movement?

Answer 10

they interact with motor molecules

Question 11

What are motor molecules?

Answer 11

proteins that can attach, detach, and reattach farther along the actin filament

Question 12

Give an example of a motor molecule.

Answer 12

myosin in muscle cells pull actin filaments along using the energy of ATP

myosin has both a head and a tail

the tails of several myosin molecules are joined to form a thick filament, while the heads interact with ATP and the actin filament

Question 13

How are actin filaments involved in animal cell division?

Answer 13

the two new cells form when actin, in conjunction with myosin, pinches off the cells from one another

Question 14

What are intermediate filaments?

Answer 14

roplelike assembly of fibrous polypeptides that vary according to the type of tissue

Question 15

What’s the size of intermediate filaments?

Answer 15

intermediate in size between actin filaments and microtubules that will perform a structural role in the cell

Question 16

What is the function of intermediate filaments?

Answer 16

• some support the nuclear envelope
• some support the plasma membrane
• some take par in the formation of cell-to-cell junctions

Question 17

What do intermediate filaments do in skin cells?

Answer 17

intermediate filaments made of the protein keratin, provide mechanical strength

they are dynamic structures

Question 18

What are microtubules?

Answer 18

small, hollow cylinders

have 13 rows of tubular dimers, surrounding what appears to be an empty central core

Question 19

What are microtubules made up of?

Answer 19

the globular protein tubulin, which is of the 2 types, alpha and beta

Question 20

What is the regulation of microtubule assembly controlled by?

Answer 20

a microtubule organizing centre

Question 21

What is the centrosome?

Answer 21

the main microtubule organizing centre that lies near the nucleus in most eukaryotic cells

Question 22

What do microtubules do?

Answer 22

they radiate from the centrosome, helping to maintain the shape of the cell and acting as tracks along which organelles can move

Question 23

What motor molecule are associated with actin filaments?

Answer 23

myosin

Question 24

What motor molecules are associated with microtubules?

Answer 24

kinesin and dynein

Question 25

How are microtubules involved in cell division before it occurs?

Answer 25

they disassemble and then reassemble into a structure called a spindle

Question 26

What is a spindle?

Answer 26

the spindle apparatus attaches to the chromosomes and ensures that they are distributed in an orderly manner

Question 27

Are microtubules involved during cell division?

Answer 27

yes

Question 28

How are microtubules involved after cell division?

Answer 28

the spindle disassembles and microtubules reassemble once again into their formal array

Question 29

In animal cells, what do centrosomes contain?

Answer 29

2 centrioles lying at right angles to each other

Question 30

What are centrioles involved in?

Answer 30

may be involved in the process of microtubule assembly and disassembly

Question 31

What are centrioles?

Answer 31

short cylinders of microtubules with a 9+0 pattern of microtubule triplets (ring with 9 sets of microtubule triplets with none in the middle)

Question 32

How are centrioles involved before animal cell division?

Answer 32

the centrioles replicate such that the members of each pair are again at right angles to one another

then, each pair becomes part of a separate centrosome

Question 33

What happens to centrosomes after cell division?

Answer 33

centrosomes move apart and may function to organize the mitotic spindle

Question 34

What are cilia and flagella?

Answer 34

hairlike projections that can move either in an undulating fashion, like a whip, or stiffy, like an oar

Question 35

How do unicellular organisms called paramecia move?

Answer 35

by means of cilia

Question 36

How do sperm cells move?

Answer 36

by means of flagella

Question 37

What do cilia do in the human body?

Answer 37

the cells that line our upper respiratory tract have cilia that sweep debris trapped within mucus back up into the throat where it can be swallowed or ejected, this helps keep lungs clean

Question 38

Describe cilia and flagella in eukaryotic cells.

Answer 38

• cilia are much shorter than flagella, but they have a similar construction
• both are membrane-bound cylinders
• cylinders are composed of 9 microtubule doublets arranged in a circle around 2 central microtubules
• 9+2 pattern of microtubules
• cilia and flagella move when the microtubule doublets slide past one another

Question 39

What is the shaft of a flagellum or cillium?

Answer 39

the shaft of the flagellum has a ring of 9 microtubule doublets anchored to a central pair of microtubules

contains microtubule doublets whose side arms are motor molecules that cause the projection to move