muscles

Question 1

how is F-actin (filamentous) assembled?

Answer 1

actin subunits head to tail assemble to form tight righthanded helix

Question 2

what is myosin II composed of?

Answer 2

two heavy chains and four light chains (dimerization when two alpha helices wrap around each other)

Question 3

how does myosin walk towards tail of actin?

Answer 3

with energy from binding and hydrolyzing ATP (head)

Question 4

how does actin tail interactions work in skeletal muscle?

Answer 4

form large bipolar thick filaments with lots of myosin heads orientated in opposite directions

Question 5

how does skeletel muscle cells (fibers) formed?

Answer 5

fusion of many muscle cell precursors

Question 6

what are sarcomeres formed from?

Answer 6

miniature array of parallel and partly overlapping thin and thick filaments

Question 7

what is a myofibril?

Answer 7

cylindrical stucture that is often as long as the muscle cell
made of repeated chain of tiny sacromeres

Question 7

what is the sliding filament theory?

Answer 7

muscle fiber contracts when myosin filaments pulla ctin filaments closer together to shorten sacromeres within fiber

Question 8

how are myosin and actin filaments packed together?

Answer 8

with crystalline regularity

Question 8

what is sacromere shortening caused by?

Answer 8

myosin filaments sliding past actin thin filaments (no change in length of either)

Question 9

where are filaments anchored in sarcomeres?

Answer 9

thin filaments (actin) anchored + ends to Z disc
thick filaments anchored to M line

Question 10

what does alpha-actinin do?

Answer 10

holds actin thin filaments together in regularly shaped bundle

Question 11

what is the Z disc built from?

Answer 11

CapZ

Question 12

what is titin?

Answer 12

acts as molecular sping
has long serires of immunoglobulin domains that unfold as stress is applied
keeps thick filaments poised in middle of sarcomere

Question 13

what does nebulin do?

Answer 13

maintains length and stability of thin filaments

Question 14

what initiates muscle contraction?

Answer 14

sudden rise in cytosolic Ca2+ concentration

Question 15

what does the signal from the nerve trigger (muscle contraction)?

Answer 15

action potential in plasma membrane which spreads to T tubules and extend around each myofibril

Question 16

what happens when incoming action potential to T tubule?

Answer 16

activates Ca2+ channel in membrane, opens Ca2+ release channel in sarcoplasmic reticulum membrane

Question 17

what does Ca2+ flooding in cytosol iniate?

Answer 17

contraction of myofibrils through the troponin complex and tropomyosin

Question 18

what is tropomyosin?

Answer 18

elongated protein that binds along groove of actin filament helix

Question 19

what is troponin?

Answer 19

a complex of three polypeptides

Question 20

what happens in resting muscle?

Answer 20

troponin pulls tropomyosin into position on actin filament interfering with myosin heads

Question 21

what is stretch activation?

Answer 21

intrinsic length sensing mechanism that allows muscles to function with autonomous regulation (no Ca)