Mitochondria metabolic functions

E. Gluconeogenesis requires ATP, which is in short supply, turning up the catabolism of glucose to lactate in the absence of an intact electron transport chain. ADP cannot be transported into the mitochondrion because ATP, its antiporter partner, isn t made by oxidative phosphorylation as a result of cyanide inhibition of cytochrome oxidase. Metabolism of fatty acids and ketone bodies requires a functional electron transport chain for their metabolism, and these possibilities are also ruled out. 

Botelho MV, Capela J, Soares P, et al. Somatic and germline mutation in GRIM-19, a dual function gene involved in mitochondrial metabolism and cell death, is linked to mitochondrion-rich (Hurthle cell) tumours of the thyroid. Br J Cancer. 2005 92 1817-1818. 

The enzymes are functionally similar to their mammalian counterparts. The dihydro-orotate oxidase, unlike that of the kinetoplastids, is associated with the parasite mitochondrion (99). However, the last two enzymes, the cytoplasmic orotate PRTase and OMP decarboxylase, are separate enzymes instead of being arranged in a bifunctional complex as is found in mammalian cells (99,100). Metabolic studies indicate that CTP synthetase must be present. 

One of the characteristic features of mammalian cells in contrast to bacteria is their compartmented structure. Due to the existence of various cell organelles, for example, nucleus, mitochondrion, endoplasmic reticulum (ER), and Golgi apparatus, mammaUan cells are divided into compartments with specific functions. Nevertheless, several transport mechanisms form connections between the different compartments and show that local processes are part of a global cellular network. This chapter focuses on the basics of cellular structure and metabolism in the context of the global cellular network. 

Because the mitochondrial membrane is impermeable to ATP/ADP and NAD/NADH, two transport systems are necessary for the function of the R.c. One is the ATP/ADP carrier, which effects facilitated exchange diffusion, and the other is a metabolic shuttle (see Hydrogen metabolism) which allows reducing equivalents generated in the cytoplasm to enter the mitochondrion. 

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