Final answer:
The part of ATP synthase composed of the stalk and a knob is the a) F1 complex, which includes the α and β subunits arranged in a ring and the central γ subunit.
Step-by-step explanation:
Components of ATP Synthase:
The part of ATP synthase that is composed of the stalk and a knob is the option a) F1 complex.
The F1 complex protrudes into the matrix of the mitochondria and is associated with ATP synthesis. It includes a set of three α and three β subunits arranged in a ring, with a central γ subunit that connects to the rotary part of the enzyme (the Fo complex) acting as the axis. This central γ subunit along with other components forms the rotor. The F1 complex performs the synthesis of ATP through conformational changes in the β subunits during rotation. Therefore, it can be visualized like a mushroom head, with the F1 complex forming the knob and the connection to the Fo complex forming the stalk.
On the other hand, the F0 complex is hydrophobic and embedded in the mitochondrial inner membrane, containing subunits that form a proton channel and make up the rotor portion that couples proton flow to the rotation necessary for ATP production.