**Question:** Mitochondrial membrane proteins contain transport of:

**Core Concept:** Mitochondria are essential cellular organelles involved in energy production through the process of cellular respiration. Their outer membrane is primarily composed of transporters, which facilitate the movement of molecules across the membrane. These transporters are integral proteins embedded in the membrane.

**Why the Correct Answer is Right:** Mitochondrial membrane proteins play a crucial role in transporting essential molecules, such as nutrients, ions, and waste products, across the mitochondrial membrane. The correct answer (D) refers to the specific type of transporters found in the mitochondrial membrane: carrier proteins.

Carrier proteins are a group of integral membrane proteins that facilitate the passive transport of molecules across the mitochondrial membrane through a process called facilitated diffusion. This process does not require energy input and is driven by the concentration gradient of the molecules involved.

**Why Each Wrong Option is Incorrect:**

A. Mitochondrial membrane proteins are not involved in active transport, which requires energy input. Active transport is facilitated by ATP-dependent transporters, such as ATPases, and not carrier proteins.

B. Mitochondrial membrane proteins are not involved in secondary active transport, which is also ATP-dependent and involves the transport of one molecule against its concentration gradient.

C. Mitochondrial membrane proteins do not directly facilitate active transport, but rather passive transport through carrier proteins.

**Clinical Pearl:** Understanding the types of transporters in mitochondrial membranes is essential for understanding cellular energy production and the role of mitochondria in various physiological processes, such as glucose uptake, amino acid transport, and ion regulation. For example, glucose is transported into the mitochondria via carrier proteins to be utilized in the citric acid cycle and oxidative phosphorylation.

**Correct Answer:** D. Carrier proteins