Short and medium chain fatty acids do not require help from membrane transporters to enter the mitochondria. Longer chain fatty acids do.
In this video I discuss about the carnitine system:
- in the cytosol, activated fatty acids are esterified to CoA and transesterified to carnitine (via CPT-I)
- fatty acyl-carnitine moves into the intermembrane space of the mitochondria
- they enter the mitochondrial matrix through facilitated diffusion by carnitine/acyl-carnitine translocase
- carnitine is freed and fatty acyl CoA reform (via CPT-II); carnitine can diffuse back across the IMS through the same translocase
- the process can take place all over again
The video makes it easier to understand.