The region at the ends of the $A$-band of two adjoining sarcomeres is called

During muscle contraction,$(P)$ get reduced whereas $(Q)$ retain the length. Here $P$ and $Q$ are $-$

How is $G$-actin converted into $F$-actin?

In a $A$ state,the edge of thin filaments on either side of thick filaments $B$ overlap the free ends of $C$ filaments leaving the central part of thick filaments. This central part of thick filament,not overlapped by thin filaments is called $D$ zone.
Choose the correct options to fill the gaps $A, B, C$ and $D$,so as to complete the given $NCERT$ statement.

$A$ sarcomere is defined as the segment between:

$ATPase$ enzyme needed for muscle contraction is located in