Sarcomere structure Flashcards
Describe the arrangements of muscle fibres
Endomysium separates individual muscle fibres
Perimysium lies between fasiculi (bundles of fibres)
Epimysium is the dense sheeth covering the surface
Myosatellite cells give rise to what cells?
Myoblasts which will mature into myoctyes. This differentiation process is blocked by myostatin
What are myofibrils composed off?
Mainly actin and myosin
What is a sarcomere
The portion of a myofibril that lies between two successive Z disks
What is a Z disk?
The disk in the middle of an I band. It is involved in differentiating sarcomeres
What does the H zone consist of?
Myosin only
What does the I band consist of?
Actin only
What does the A band consist of?
Myosin and Actin
What is the function of the M line?
To hold thick myosin strands together
Describe the structure of myosin
Its tail consists of two heavy chains intertwined which lead up to two gloubar heads which extend out forming cross-bridges. The heads contain light bridges along with ATP (myosin-ATPase) and Actin binding sites
Describe the structure of Actin
An intertwined contractile protein which is closely associated with Tropomyosin and Troponin. Each G actin has a binding site for myosin
Describe the function of Tropomyosin
It is a regulatory protein which overlaps the myosin binding sites on actin and therefore inhibits interaction when in a relaxed state.
Describe the function of troponin
It is a regulatory, calcium binding protein which forms a complex with actin and tropomyosin.
Troponin reversibly binds to calcium which changes its conformations to pull tropomyosin away from myosin binding sites allowing for the interaction between actin and myosin.
What is the role of Nebulin?
It helps align actin
What is the role of Titin?
It provides elasticity and stabilizes myosin
Name the structural proteins
Titin, Z-line proteins (alpha actinin), M-line proteins (myomesin, M-protein) and Nebulin
Name the contractile proteins
Acin, Myosin, Troponin complex and Tropomyosin
What gives cardiac and skeletal muscle their striated appearance
Myofibrils
Draw the cross sections through a sarcomere
See week one lecture
What are T-tubules?
They are extensions of the cell membrane, its walls are continuous with the sarcolemma so the fluid within the tubules is continuous with the external environment
What are the sarcoplasmic reticulum and terminal cisternae
Sarcoplasmic reticulum (SR) is the smooth ER of a muscle cell. The terminal cisternae is the part of the SR that is next to the T-tubules
The T-tubule and sarcoplasmic reticulum are connected by what junctions. What proteins are involved in this?
The protein in the T-tubule is a voltage sensitive calcium channels called dihydropyridine. The protein in the SR membrane is known as the ryanodine receptor which forms a Ca channel
