How does pyruvate enter the mitochondrion?
A) active transport
B) diffusion
C) facilitated diffusion
D) through a channel
E ) through a pore
The correct answer and explanation is :
The correct answer is:
A) Active transport
Explanation:
Pyruvate, the end product of glycolysis, must enter the mitochondrion for further metabolism in the citric acid cycle (Krebs cycle). However, because pyruvate is a charged molecule (a negatively charged carboxylate ion), it cannot simply diffuse across the mitochondrial membrane. Instead, its transport into the mitochondrial matrix requires active transport.
Mechanism of Pyruvate Transport:
- Transport across the Outer Membrane
- The outer mitochondrial membrane contains large, non-specific porins (voltage-dependent anion channels, or VDACs) that allow small molecules like pyruvate to pass freely.
- Transport across the Inner Membrane
- The inner mitochondrial membrane is highly selective and lacks such pores. Pyruvate requires a specific transport protein called the mitochondrial pyruvate carrier (MPC) to cross into the mitochondrial matrix.
- The MPC functions as an active transport system that utilizes the proton gradient generated by the electron transport chain (ETC).
- This process is a type of secondary active transport, where pyruvate is co-transported with protons (H⁺), using the electrochemical gradient as an energy source.
Importance of Pyruvate Transport:
- Once inside the mitochondrial matrix, pyruvate undergoes oxidative decarboxylation by the pyruvate dehydrogenase complex (PDC) to form acetyl-CoA, which then enters the citric acid cycle.
- Efficient pyruvate transport is crucial for ATP production and metabolic regulation.
Thus, because pyruvate transport depends on energy (proton gradient), the correct answer is active transport (A), not diffusion, facilitated diffusion, or passage through a channel or pore.