Week 13: (B) Coupling and Skeletal Muscle Contraction Flashcards
What are the 3 proteins of the thin filament?
Troponin, Actin, Tropomysosin
what are the 3 types of Troponin?
Troponin T, I & C
what does Troponin T do?
binds to trypomyosin-
What does Troponin I do?
bind to actin inhibit contraction
What does Troponin C do?
binds to Ca+
Structure of Actin?
double stranded alpha-helical
Does actin have a binding site?
BS for attachment with myosin cross bridge
What happens to troponin when NOT bound to Ca+?
stabilises tropomyosin in its blocking position over the actin cross bridge BS.
Tropomyosin structure?
2 stranded helixes wrap around each other to form a ribbon, this wraps around the actin and the troponin attached to this
What chains are present in thick filaments?
2 heavy chains, 2 regulatory light chains, 2 chains alkali chains.
What does the Alkali light chain do on the myosin head region?
stabilises head region
What does the regulatory light chain do on the myosin head?
Regulates ATPase activity of myosin
What regulates ATPase activity of myosin?
RLC which is in turn regulated by phosphorylation by kinase
what does the heavy chain do on the head region of myosin?
binding site for actin
binding and hydrolysing ATP
what can the heavy head region also be called?
S1
What do the heads of myosin form?
cross-bridge
what type of myosin attached to actin?
Myosin-ii
what is step 1 of a muscle contraction?
myosin-ii heads bind to actin, cross-bridge becomes distorted, myosin heads detach from myosin
What happens to ATP for myosin heads to move away?
Hydrolysis of ATP
How is a muscle contraction triggered?
increase Ca2+ concentration
What does increased Ca2+ concentration do?
removes inhibition of cross bridge cycling
How does Ca2+ modulate contractions?
regulatory proteins act together to inhibit myosin and actin interactions
What does Ca+ bind to to stimulate a contraction?
Troponin C. release inhibition of Troponin I (bound to actin to block cross-bridge)
Where does ATP bind on Myosin?
Heavy chain
What happens when ATP is bound to Myosin? (pt 1)
Reduce affinity for actin, detachment
How is a muscle cell relaxed?
ATP bound to Myosin
What happens when hydrolysis of ATP on myosin occurs? (pt 2)
Remains on the myosin, myosin swings back.
cocked state
lines up with a new actin monomer
When is the muscle relaxed?
ATP is bound, Myosin head swings back
when will the cross-bridge form?
If intracellular Ca2+ concentrations are high enough
What happens to ADP + Pi when cross-bridge is formed?
inorganic phosphate released, triggers power stroke
What happens in the power stroke?
Myosin head confo change, move ~45 degrees about the hinge, pulls actin towards tail of myosin
what happens after the power stroke?
ADP is released, myosin complex left in a rigid state.
How can the myosin-actin complex be relaxed?
ATP binding to heavy chain on head of myosin= relaxed
Do the thin of thick filaments move when contracting?
Thin slide over thick
Does the sarcomere shorten?
YES as thin filaments move closer together
Does the A band change width?
no, stays the same width
does the I band width decrease?
Yes, don’t overlap thick so shorten
does the H zone decrease?
Yes, similarly to the M line
Does the Z line decrease?
Yes, distance between decrease
What happens in riggor mortis?
Ca2+ rise (starts around 3-4hrs after death, complete in 12hrs)
Allow actin to bind to myosin
No ATP produced from the death body so stuck in rigid state
what happens when Ca2+ binds to Troponin on tropomyosin?
Binds to Troponin C to remove the blocking Troponin I by shifting it to expose the Myosin binding site.
Also TnT moved away from binding site into a groove
