cytoskeleton I

Question 1

what is the function of the cytoskeleton?

Answer 1

spatial and mechanical function

Question 2

what makes up the cytoskeleton?

Answer 2

protein filaments and tubules

Question 3

what is the purpose of the cytoskeleton?

Answer 3

cell shape, cell movement, internal structure, intracellular transport, intercellular communication, organelle and cell anchoring

Question 4

what are the three types of cytoskeletal proteins?

Answer 4

actin, microtubules, intermediate filaments

Question 5

what 4 functions does actin have?

Answer 5

cell surface shape, whole cell locomotion, links transmembrane proteins to cytosolic proteins, pinches cell shut after division

Question 6

what 3 functions do microtubules have?

Answer 6

positions organelles, intracellular transport, needed for cell division

Question 7

what 2 functions do intermediate tubules have?

Answer 7

provide mechanical strength, line inside of nuclear envelope

Question 8

which accessory proteins are associated with microtubules?

Answer 8

Motor proteins (dynein, kinesin)

Question 9

where is actin highly concentrated?

Answer 9

cortex of cytoplasm

Question 10

which 2 proteins interact during cell division?

Answer 10

actin and microtubules

Question 11

why must cytoskeleton be dynamic and adaptable? when is this most prevalent?

Answer 11

because of constant changes in cells, esp. during development, cell cycle, phagocytosis or other specific cellular function

Question 12

what does it mean to have strength in numbers? why is this important?

Answer 12

Single filaments are prone to easy breaking so multiples are needed; multiple protofilaments needed to make microtubule thermally stable

Question 13

why can’t microtubules just have strong covalent bonds within a single protofilament? what kind of bonds do they have instead?

Answer 13

it wouldn’t allow them to disassemble quickly; hydrophobic interactions and noncovalent bonds

Question 14

how do motor proteins and microtubules interact? how is it done? what protein is responsible for this?

Answer 14

dynein and kinesin attach to microtubules and “walk” along it; repeated rounds of ATP hydrolysis; tubulin

Question 15

what makes up an actin subunit?

Answer 15

G-actin , carrying an ATP or ADP

Question 16

how are actin subunits assembled? what do they form?

Answer 16

assemble head to tail to form F-actin

Question 17

how do actin subunits demonstrate directionality?

Answer 17

Actin subunits are polar and have structurally different ends (plus end and minus end)

Question 18

how would you describe minus end of an actin subunit?

Answer 18

Slower-growing minus end (pointed end)

Question 19

how would you describe plus end of an actin subunit?

Answer 19

Faster-growing plus end (barbed end), subunits are added here

Question 20

where do actin filaments form a complex?

Answer 20

actin filaments and the motor protein myosin

Question 21

what is filament nucleation? where is it used? how?

Answer 21

process of initial aggregation (clustering); actin filaments; Subunit assembly and disassembly where needed

Question 22

How does branching nucleation work and how does it form the actin web?

Answer 22

Formation Arp2 and 3 (protein complex) serve as nucleation hubs, binding to
a preexisting actin filament to form a web, it then acts as a plus end for monomer addition

Question 23

Give an example of how specialized cells can use cytoskeletal elements to perform their functions.

Answer 23

Myofibrils in striated skeletal muscle cells consist of sarcomeres, here actin and myosin interact

Question 24

what is each band in one sarcomere made of?

Answer 24

light bands= actin only dark bands = actin and myosin

Question 25

what is myosin and how does it function? how does it do this?

Answer 25

motor protein that “slides” along actin polymers for muscle contraction; Uses ATP hydrolysis

Question 26

Why and where is the protein complex troponin important?

Answer 26

Critical for control of muscle contraction; skeletal and cardiac muscles

Question 27

what steps does troponin take to cause a muscle to contract?

Answer 27

Calcium binds troponin, which causes tropomyosin (an accessory muscle protein) to move away from actin, so it can bind to myosin to shorten sarcomere and contract muscle

Question 28

why is troponin measured clinically in cardiac muscles?

Answer 28

If troponin levels are high in the blood, it could be a sign that a heart attack has occurred