week 3: 10.3 continued Flashcards
A band
regions of overlapping thick (myosin) and thin (actin) filaments
contains three sub divisions
three sub divisions of the A band
M line
H band
zone of overlap
M line
-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
H band
-lighter region on either side of the M line
- thick filaments only
zone of overlap
dark region where thin filaments are located between thick filaments
- three thick filaments surround each thin filament
- six thin filaments surround each thick filament
T tubules and sarcomere arrangement
T tubules encircle each sarcomere
where are the triads containing the T tubules located
zones of overlap, at the edges of the A band
significance of triad location
calcium ions released by the SR enter region where thick and thin filaments can interact
I band
region of the sarcomere that contains thin filaments
what does the I band extend from
A band of one sarcomere to A band of next
Z line and I band interaction
Z line bisects I band and marks boundaries between adjacent sarcomeres
Z line consists of
actinins proteins
interconnect thin filaments of adjacent sarcomeres
titin
extends from tips of thick filaments to attachment sights at Z line
function of titin
-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
thin filaments molecular structure
5-6 nm diamneter
1μm long
contains 4 main proteins: F-actin, nebulin, tropomyosin, troponin
Filamentous actin
twisted strand composed of two rows of 300-400 individual globular molecules of G actin
nebulin
-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
what does each G-actin molecule contain
active sight where mysoin can bind
binding sight on G-actin in resting state
-troponin-tropomyosin complex prevents myosin binding
- strands of tropomyosin cover active sights on G-actin preventing actin-mysosin interaction
tropomyosin
double stranded protein that covers 7 active sights
bounded to one molecule of troponin midway along its length
troponin
3 globular subunits
how are troponin and tropomyosin locked into a complex
one globular subunit of troponin binds to tropomyosin locking them together as a complex
how is the troponin- tropomyosin complex locked into position
troponins second globular subunit binds to G actin holding complex into position