Molecular contraction mechansism

12 important questions on Molecular contraction mechansism

Which 3 muscle types exist?

Cardiac muscle (heart)
Skeletal muscle (leg, arm etc)
Smooth muscle (intestines)

--> all contraction by actin-myosin interaction

What are the main functional differences between the muscle types?

See table

What is the anatomy of the cardiomyocyte?

Exists of myofilaments, myofibrils and mitochondria
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What is the hexagonal lattice structure?

Each myosin filament is connected to 6 actin filaments

What is the function of titin?

Structural: Keeps myosin centered in the sarcomere, extends from Z-line to M-line (half sarcomere)
Functional: works as (non-linear) spring
- increased stiffness during stretch
- passive 'restoring force' during shortening

What is the anatomy of a myosin filament?

Head, hinge (neck) and tail region
thick filament

What is a myosin II molecule?

- pair of identical myosin I molecules, each composed of a myosin heavy chain with tail, hinge and head domain and 2 myosin light chains

What is the function of myosin light chains?

Have structural (stabilising) and regulatory funciton.
MLC-2 phospholylation leads to cross-bridge interaction

What is the function of myosin head?

Binding places for actin (to form cross-bridges) and for ATP

What controls the actin-myosin interaction? And how?

Intracellular Ca2+ controls interaction
The troponin complex regulates the binding:
- tropomyosin is connected to actin, TnT connects to tropomyosin, TnC binds to TnT and TnI binds to TnC and actin. 

TnI inhibits binding of myosin by blocking the binding site. Binding of Ca2+ to TnC makes the myosin binding site available

What is the cycle of the cross-bridge between myosin and actin?

1. Attached state (rigor mortis), ATP binding to myosin head
2. Released state, ATP hydrolysis
3. Cocked state, cross-bridge formation
4. Weak cross-bridge state, P release
5. Strong cross-bridge state, power stroke
6. Post power stroke state, ADP release
7. Attached state

How does the myofilament generates force (tension) or movement?

Movement by cross-bridge cycling
Forse when filament sliding is prevented

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