Inner membrane

The correct answer is option 'B', the inner membrane.

Overview of Mitochondria
Mitochondria are double-membraned organelles found in eukaryotic cells that are responsible for producing energy in the form of ATP through cellular respiration. They have an outer membrane and an inner membrane, which are separated by an intermembrane space. The inner membrane is highly folded, forming structures called cristae, which increase the surface area available for ATP production. The space enclosed by the inner membrane is called the matrix.

Accumulation of Proteins
Proteins play crucial roles in the function of mitochondria, and they are synthesized both within the mitochondria and in the cytoplasm before being imported into the organelle. Once inside the mitochondria, proteins are targeted to different compartments depending on their specific functions.

Protein Import into Mitochondria
Protein import into mitochondria occurs through specific mechanisms involving protein translocases located in the outer and inner membranes. The import process ensures that proteins are correctly targeted to their respective compartments within the organelle.

Outer Membrane Proteins
Proteins that are targeted to the outer membrane of mitochondria contain specific targeting sequences, such as a signal peptide, which allow them to be recognized and transported by the translocase of the outer membrane (TOM complex). These proteins are translocated across the outer membrane and inserted into it.

Intermembrane Space Proteins
Some proteins are targeted to the intermembrane space of mitochondria. These proteins contain a signal peptide that directs them to the TOM complex in the outer membrane. Once in the intermembrane space, these proteins can perform various functions, such as participating in redox reactions or assisting in protein import.

Inner Membrane Proteins
Proteins that are destined for the inner membrane or matrix of mitochondria have specific targeting sequences that allow them to be recognized and transported by the translocase of the inner membrane (TIM complex). The TIM complex facilitates the translocation of these proteins across the inner membrane into the matrix or insertion into the inner membrane.

Conclusion
In conclusion, proteins accumulate in the inner membrane of mitochondria. The inner membrane is responsible for ATP synthesis and contains proteins that are involved in this process. These proteins are imported into the mitochondria and targeted to the inner membrane through specific mechanisms involving protein translocases. Understanding the mechanisms of protein import and localization within mitochondria is essential for understanding their function and the role they play in cellular energy production.