Thermal ratchet model > Two models have been proposed to explain how ATP hydrolysis by mitochondrial hsp70 drives protein import.In the thermal ratchet model (Figure 12-28A), the emerging chain slides back and forth in the TIM23 translocation channel by thermal motion. Each time a sufficiently long portion of the chain is exposed in the matrix, an hsp70 molecule binds to it, preventing further backsliding and thereby making the movement directional. Thus, a hand-over-hand binding of multiple hsp70 proteins translocates the polypeptide chain into the matrix. ![Image- thermal ratchet]( What does thermal motion mean here? I will be obliged if somebody could explain it.

To repeat @Malijam comment, by `thermal motion` it is referring to the "random giggling" of molecules.

Temperature difference is nothing but a change in the frequency at which molecule move randomly. This movement has no specific direction. If a given molecule is prevented from moving into one specific direction (due to attachement to another molecule) but allowed to move into another, then the molecule will move directionally pushed by nothing but its thermal kinetic. This create a so called thermal ratchet.