Cells alive 3- cytoskeleton

Question 1

what are the functions of the cytoskeleton?

Answer 1

• support
• movement
• resistance to mechanical forces

Question 2

what are the 3 types of filaments in a cytoskeleton?

Answer 2

-microfilaments
- intermediate filaments
- microtubules

Question 3

what are the monomers in microfilaments?

Answer 3

actin

Question 4

what size are microfilaments

Answer 4

v small: 5-9nm

Question 5

what are microfilaments made of and how are they assembled?

Answer 5

made of globular proteins called actin which assemble into two stranded helical polymers

Question 6

where do you find microfilaments?

Answer 6

they are dispersed through the cell but concentrated beneath the cortex

Question 7

how are microfilaments distributed?

Answer 7

the actin anchors to the mesh proteins in the cortex and distribute like a web

Question 8

what is the function of microfilaments?

Answer 8

cell shape and motility

Question 9

are microfilaments dynamic?

Answer 9

yes

Question 10

what is the size of intermediate filaments?

Answer 10

10nm diameter (hollow tube)

Question 11

are intermediate filaments more or less dynamic than microfilaments?

Answer 11

less

Question 12

what is the structure of intermediate filaments?

Answer 12

extended alpha-helical regions wind together into dimers which then associate into tetramers, these wind together to form rope-like fibres

Question 13

what is a dimer?

Answer 13

2 joined monomers

Question 14

what is a tetramer

Answer 14

4+ subunits

Question 15

give examples of intermediate filaments

Answer 15

keratins in epithelial cells
desmin in muscle cells

Question 16

what is the function of intermediate filaments?

Answer 16

mechanical support of cell structures

Question 17

what is the size of microtubules?

Answer 17

25nm in diameter

Question 18

what are microtubules made of?

Answer 18

globular proteins called tubulin

Question 19

what is the minimal subunit of microtubules?

Answer 19

dimer of alpha beta subunit

Question 20

how is tubulin formed?

Answer 20

alpha and beta tubulin subunits dimerise to form tubulin

Question 21

what is the structure of microtubules?

Answer 21

• long and straight
• one end (-) is attached to a microtubule organising centre (MTOC) while the other end (+) grows and shrinks

Question 22

what protein “walks” along the microtubule

Answer 22

motor proteins

Question 23

are intermediate filament monomers globular?

Answer 23

no

Question 24

typically microtubules are attached to one point within the cell; what is it called?

Answer 24

microtubule organising centre

Question 25

true or false...Monomers are added to the filaments of the cytoskeleton by covalent interactions.

Answer 25

false

Question 26

within the cytoskeleton what is the concentration at which the rate of monomer addition equals the rate of removal known as?

Answer 26

The critical concentration

Question 27

Microtubules and actin filaments have a fast growing and a slow growing end. Name 2 mechanisms by which this is achieved

Answer 27

- conformation change - nucleotide hydrolysis

Question 28

Name one toxin or drug which affects the assembly or disassembly of the cytoskeleton.

Answer 28

vincristine

Question 29

Which of the following are examples of cytoskeletal motor proteins? - tublin - dynein - actin - myosin - kinesin

Answer 29

- dynein - myosin - kinesin

Question 30

what are the cytoskeletal elements to these motor proteins - dyneins - myosins - kinesins

Answer 30

dyneins = microtubules kinesins = microtubules myosins = actin filaments

Question 31

Put the following in order: Myosin head bound to actin filament... ATP hydrolysed Myosin head changes shape to move forwards Phosphate released and mysoin reattaches to actin Myosin releases actin ADP released and conformation change (power stroke) Myosin binds ATP

Answer 31

1. myosin binds ATP 2. myosin releases actin 3. ATP hydrolysed 4. myosin head changes shape to move forwards 5. phosphate released and myosin reattaches to actin 6. ADP released and conformation change (power stroke)

Question 32

Name two organelles which are held in position by the actions of motor proteins on microtubules.

Answer 32

golgi endoplasmic reticulum

Question 33

Cytoskeletal elements are central to cell motility. Match the form of motility to the element: - flagella and cilia - muscle contraction - cell crawling - microvilli in gut with actin filaments microtubules intermediate filaments

Answer 33

flagella and cilia = microtubules muscle contraction = actin filaments cell crawling = actin filaments microvilli in gut = actin filaments

Question 34

What is the order of the three cytoskeletal elements in order of size? (smallest to largest)

Answer 34

microfilaments, intermediate filaments, microtubules

Question 35

What is the main role of microtubules?

Answer 35

Organelle positioning and intracellular transport

Question 36

Actin filaments and microtubules have fast growing ends. How is this achieved?

Answer 36

nucleotide hydrolysis

Question 37

Myosin, Kinesin, and Dynein are examples of what?

Answer 37

motor proteins

Question 38

Motor proteins on microtubules hold the following organelle(s) in position: ER Golgi Chromosome All of the above

Answer 38

all of the above

Question 39

What is vincristine?

Answer 39

a chemotherapy drug that inhibits tubulin polymerisation

Question 40

What is the default route taken by a protein once it has completed its journey through the Golgi?

Answer 40

constitutive exocytosis

Question 41

How are cells protected from their own lysosomal hydrolases?

Answer 41

these enzymes only work within a membrane at a specific pH range

Question 42

What coat does your protein need if it wants to go from the ER to the Golgi?

Answer 42

COP II

Question 43

What coat does your protein need if it wants to go from the Golgi to the ER?

Answer 43

COP I

Question 44

What coat does your protein need if it wants to go from the plasma membrane to the endosome?

Answer 44

Clathrin

Question 45

What is the name of the protein that links clathrin to the cargo receptor?

Answer 45

adaptin

Question 46

What is the name of the protein that cleaves off the newly formed vesicle?

Answer 46

dynamin

Question 47

What is the process via which certain components can be retrieved from the plasma membrane following exocytosis?

Answer 47

endocytosis

Question 48

How is myosin moving along actin filaments related to muscle contraction?

Answer 48

When a myosin head pulls against actin the sacromere shortens. It is chains of sacromeres that form myofibrils which bundle together to form muscle fibres that stretch the length of the muscle cell.

Question 49

How do kinesins move along microtubules?

Answer 49

It has two globular heads that interacts with the cytoskeleton. Kinesin moves from the negative end of the microtubule to the positive. The globular heads use ATP hydrolysis to power the conformation changes that walk the motors along the microtubules. Each head attahes and releases itself alternately, like moving one foot then the other.

Question 50

How are kinesins moving related to intracellular transport and organisation?

Answer 50

The motor proteins are attached to the organelle or vesicle that they are moving so that as the motor protein moves, so does the organelle.

Question 51

What are the types of cellular motility?

Answer 51

Cell crawling Phagocytosis Microvilli

Question 52

How are microvilli related to cellular motility?

Answer 52

Bundles of actin fibres extend to the tip and there are myosins attached to the cell membrane that 'walk' along the actin filaments, causing the microvillus to wave.

Question 53

What is it called when filaments polymerise and depolymerase rapidly?

Answer 53

nucleation

Question 54

Explain what nucleation is.

Answer 54

Hardest part because bonds between subunits need to be broken. Occurs in lag phase.

Question 55

What occurs in growth phase?

Answer 55

elongation

Question 56

At equilibrium, what is the critical concentration? How do you work it out?

Answer 56

The concentration of monomers free in the cytoplasm after elongation cc = Koff/Kon cc is often greater at one end, which elongates faster. If the concentration of free monomers drops then this end also depolymerises fastest. This is the plus end.

Question 57

Give 3 examples of how the cytoskeleton can hold a tissue together?

Answer 57

Tight junctions seal epithelial membranes and limit the passage of molecules. They contribute to the maintenance of cell polarity Anchoring junctions (can attach cells to each other using adherins junctions and desmosomes. They can bind cells to the extracellular matrix using local adhesions and hemi-desmosomes Gap junctions (directly connect cytoplasm of adjacent cells, hollow junction is made from connexins

Question 58

What type of myosin makes muscles contract?

Answer 58

myosin II

Question 59

what motor proteins bind to microtubules and where do they move?

Answer 59

kinesin moves from - to + dynein moves + to -