Question

Compare and contrast the functions of the malateaspartate and glycerol- 3 -phosphate mitochondrial shuttle systems.

Short answer

Question: Compare and contrast the functions of the malate-aspartate shuttle system and the glycerol-3-phosphate shuttle system in cellular respiration. Answer: Both the malate-aspartate and glycerol-3-phosphate shuttle systems transfer reducing equivalents (NADH) from the cytosol to the mitochondria for cellular respiration. The malate-aspartate shuttle is more efficient in ATP production because it generates 3 ATP molecules per NADH molecule, while the glycerol-3-phosphate shuttle generates 2 ATP molecules per NADH molecule due to FADH2 involvement. As a result, the malate-aspartate shuttle is predominantly found in tissues with high energy requirements, like the liver, heart, and kidneys, while the glycerol-3-phosphate shuttle is more common in tissues with lower energy requirements, such as skeletal muscles and the brain.

Step-by-step solution

Briefly describe the Malate-Aspartate Shuttle System

The malate-aspartate shuttle system is a set of biochemical reactions that help transfer reducing equivalents (NADH) from the cytosol to the mitochondria. It is a reversible process that involves the interconversion of malate and aspartate, and the transport of these molecules across the mitochondrial membrane. The process generates NADH within the mitochondrial matrix, which can participate in oxidative phosphorylation to produce ATP.

Briefly describe the Glycerol-3-Phosphate Shuttle System

The glycerol-3-phosphate shuttle system is another biochemical pathway that transfers reducing equivalents from the cytosol to the mitochondria. It involves the conversion of dihydroxyacetone phosphate (DHAP) to glycerol-3-phosphate in the cytosol by cytosolic glycerol-3-phosphate dehydrogenase, which also facilitates the transfer of electrons from NADH to glycerol-3-phosphate. In the mitochondria, glycerol-3-phosphate is reconverted to DHAP, and the electrons are passed to the electron transport chain, generating FADH2.

Compare the efficiency of both shuttle systems

The most significant difference between the malate-aspartate and glycerol-3-phosphate shuttle systems lies in their efficiency in generating ATP. In the malate-aspartate shuttle, NADH generated in the mitochondria directly participates in the electron transport chain, resulting in the production of 3 ATP molecules per NADH molecule. However, in the glycerol-3-phosphate shuttle, the electrons are passed onto FADH2, which results in the production of only 2 ATP molecules per NADH molecule. Thus, the malate-aspartate shuttle is more efficient in ATP production compared to the glycerol-3-phosphate shuttle.

Compare the tissue distribution of both shuttle systems

The malate-aspartate shuttle system is predominantly found in tissues with high energy requirements, such as the liver, heart, and kidneys, due to its higher efficiency in ATP production. In contrast, the glycerol-3-phosphate shuttle system is predominantly found in tissues with relatively lower energy requirements, such as skeletal muscles and the brain, where the less efficient conversion of NADH to ATP is sufficient for energy needs.

Summary of the comparison and contrast

The malate-aspartate and glycerol-3-phosphate shuttle systems both serve to transfer reducing equivalents from the cytosol to the mitochondria, aiding in cellular respiration. The primary difference between the two systems is their efficiency in ATP production, with the malate-aspartate shuttle being more efficient due to direct NADH participation in the electron transport chain. As a result, the malate-aspartate shuttle is more commonly found in tissues with high energy requirements, whereas the glycerol-3-phosphate shuttle is more common in tissues with lower energy requirements.