week 3: 10.3 continued

Question 1

A band

Answer 1

regions of overlapping thick (myosin) and thin (actin) filaments
contains three sub divisions

Question 2

three sub divisions of the A band

Answer 2

M line
H band
zone of overlap

Question 3

M line

Answer 3

-centre of the A band
-proteins of the M line connect the central portion of each thick filament to neighboring thick filaments
-these dark-staining proteins help stabilise the positions of the thick filaments

Question 4

H band

Answer 4

-lighter region on either side of the M line
- thick filaments only

Question 5

zone of overlap

Answer 5

dark region where thin filaments are located between thick filaments
- three thick filaments surround each thin filament
- six thin filaments surround each thick filament

Question 7

T tubules and sarcomere arrangement

Answer 7

T tubules encircle each sarcomere

Question 8

where are the triads containing the T tubules located

Answer 8

zones of overlap, at the edges of the A band

Question 9

significance of triad location

Answer 9

calcium ions released by the SR enter region where thick and thin filaments can interact

Question 10

I band

Answer 10

region of the sarcomere that contains thin filaments

Question 11

what does the I band extend from

Answer 11

A band of one sarcomere to A band of next

Question 12

Z line and I band interaction

Answer 12

Z line bisects I band and marks boundaries between adjacent sarcomeres

Question 13

Z line consists of

Answer 13

actinins proteins
interconnect thin filaments of adjacent sarcomeres

Question 14

titin

Answer 14

extends from tips of thick filaments to attachment sights at Z line

Question 15

function of titin

Answer 15

-helps to keep thick and thin filaments in proper alignment and aids in restoring resting sarcomere length after contraction
-helps muscle fiber resist extreme stretching that would disrupt contraction mechanism

Question 16

thin filaments molecular structure

Answer 16

5-6 nm diamneter
1μm long
contains 4 main proteins: F-actin, nebulin, tropomyosin, troponin

Question 17

Filamentous actin

Answer 17

twisted strand composed of two rows of 300-400 individual globular molecules of G actin

Question 18

nebulin

Answer 18

-nebulin holds the F-actin strand together
-long strand of nebulin extends along F-actin strand in the cleft between the rows of G-actin molecules

Question 19

what does each G-actin molecule contain

Answer 19

active sight where mysoin can bind

Question 20

binding sight on G-actin in resting state

Answer 20

-troponin-tropomyosin complex prevents myosin binding
- strands of tropomyosin cover active sights on G-actin preventing actin-mysosin interaction

Question 21

tropomyosin

Answer 21

double stranded protein that covers 7 active sights
bounded to one molecule of troponin midway along its length

Question 22

troponin

Answer 22

3 globular subunits

Question 23

how are troponin and tropomyosin locked into a complex

Answer 23

one globular subunit of troponin binds to tropomyosin locking them together as a complex

Question 24

how is the troponin- tropomyosin complex locked into position

Answer 24

troponins second globular subunit binds to G actin holding complex into position

Question 25

third subunit of troponin

Answer 25

has a receptor that binds to 2 Ca2+ ions

Question 26

third troponin subunit in resting muscle

Answer 26

Ca2+ conc very low, binding sight is empty

Question 27

when can a contraction occur

Answer 27

when the troponin-tropomyosin complex changes position,
exposing active sight on actin

Question 28

when is the active sight on actin exposed

Answer 28

when calcium ions bind to receptors of troponin molecules

Question 29

thick filaments

Answer 29

10-12nm diameter
1.6 μm long

Question 30

mysoin arrangment in thick filament

Answer 30

contains approx 300 myosin molecules, each molecule made up of a pair of myosin subunits twisted around one another

Question 31

long tail of myosin bound to

Answer 31

other myosin molecules in the thick filament

Question 32

free head of myosin molecule

Answer 32

projects outwards to the nearest thin filament
two globular subunits

Question 33

how are myosin molecules arranged

Answer 33

tails pointing towards the M line
no myosin heads in H region
elsewhere on filament, myosin heads arranged in spiral each facing one of the surrounding thin filaments

Question 34

changes in sarcomere during contraction

Answer 34

A band stays the same width
Z lines move closer together
I band gets smaller

Question 35

when the ends of a myofibril are free to move,

Answer 35

sarcomeres shorten simultaneously and the ends of the myofibril are pulled towards its centre

Question 36

when one end of a myofibril is in a fixed position

Answer 36

the free (the insertion) end is pulled towards the fixed end (the origin)

Question 37

what causes bone movement

Answer 37

muscle fibre contracts, pulls on tendons collagen fibers which are embedded in the bone,