Helicase "unzips" the two strands of DNA. During DNA replication.
Answer and Explanation:
The steps of the sliding filament theory are:
Muscle activation: breakdown of energy (ATP) by myosin.
Before contraction begins, myosin is only associated with a molecule of energy (ATP), which myosin breaks down into its component molecules (ADP + P) causing myosin to change shape.
Muscle contraction: cross-bridge formation
The shape change allows myosin to bind an adjacent actin, creating a cross-bridge.
Recharging: power (pulling) stroke
The cross-bridge formation causes myosin to release ADP+P, change shape, and to pull (slide) actin closer to the center of the myosin molecule.
Relaxaction: cross-bridge detachment
The completion of the pulling stroke further changes the shape of myosin. This allows myosin and ATP to bind, which causes myosin to release actin, destroying the cross-bridge. The cycle is now ready to begin again.
The repeated cycling through these steps generates force (i.e., step 2: cross-bridge formation) and changes in muscle length (i.e., step 3: power stroke), which are necessary to muscle contraction.
Answer:
The correct answer will be option-E.
Explanation:
Chordae tendinae are the string-like structure in the heart which is composed of dense regular connective tissue called collagen and elastin proteins. They arise from the papillary muscles of the heart and branches out in the ventricle portion of the heart.
These play an important role in the closure of the AV valves to prevent the backward flow of the blood to the atria during ventricular contraction by holding cusps of the valve into the dome-shaped structure.
Thus, option-E is the correct answer.
