key term - Malate

Definition

Malate is a four-carbon dicarboxylic acid that plays a crucial role in metabolic processes, particularly in the citric acid cycle and the transport of reducing equivalents across mitochondrial membranes. It serves as both an intermediate in energy production and as a key player in the C4 and CAM pathways of carbon fixation, connecting various metabolic pathways and facilitating cellular respiration and photosynthesis.

5 Must Know Facts For Your Next Test

1. Malate is formed from oxaloacetate through the action of malate dehydrogenase during the citric acid cycle.
2. It can be transported out of the mitochondria into the cytosol via specific transporters, helping to shuttle reducing equivalents in the form of NADH.
3. In C4 plants, malate is produced in mesophyll cells and then transported to bundle-sheath cells where it releases CO2 for the Calvin cycle.
4. Malate can also serve as a storage form of carbon, allowing plants to adapt to varying environmental conditions by regulating its levels.
5. The conversion of malate back to oxaloacetate generates NADH, which can be used for ATP production during oxidative phosphorylation.

Review Questions

• How does malate function as an intermediate in the citric acid cycle, and what role does it play in energy production?
  • Malate plays a vital role in the citric acid cycle by forming from oxaloacetate through the action of malate dehydrogenase. This reaction also involves the reduction of NAD+ to NADH. Malate then undergoes oxidation back to oxaloacetate, generating another molecule of NADH and allowing the cycle to continue. The NADH produced is crucial for ATP generation during oxidative phosphorylation, making malate essential for cellular energy production.
• Discuss the importance of malate in mitochondrial transport and how it aids in cellular respiration.
  • Malate is important for mitochondrial transport as it helps shuttle reducing equivalents across the mitochondrial membrane. When NADH is generated in the cytosol during glycolysis, it cannot directly enter the mitochondria. Instead, malate is formed and transported into the mitochondria, where it can be converted back into oxaloacetate, generating NADH. This process enables the cell to utilize the reducing power from cytosolic NADH for ATP production within mitochondria, enhancing cellular respiration efficiency.
• Evaluate the role of malate in both C4 and CAM pathways of carbon fixation and its impact on plant productivity.
  • In both C4 and CAM pathways of carbon fixation, malate serves as a crucial intermediate that enhances plant productivity under varying environmental conditions. In C4 plants, malate is produced from phosphoenolpyruvate (PEP) and CO2 in mesophyll cells and transported to bundle-sheath cells, where it releases CO2 for use in the Calvin cycle. In CAM plants, malate accumulates at night when CO2 is fixed, enabling efficient carbon usage during the day while minimizing water loss. This dual functionality of malate allows these plants to optimize photosynthesis and adapt to their environments, improving overall productivity.

Related terms

Oxaloacetate: A four-carbon molecule that combines with acetyl-CoA to form citrate in the first step of the citric acid cycle.

NADH:

A reduced form of nicotinamide adenine dinucleotide, which acts as an electron carrier in cellular respiration, playing a key role in oxidative phosphorylation.

C4 Photosynthesis:

A carbon fixation pathway that allows plants to efficiently capture CO2 and minimize photorespiration, using malate as an intermediate.