Organelle-specific metabolism

Eukaryotic cell— A cell whose genetic material is carried on chromosomes inside a nucleus encased in a membrane. Eukaryotic cells also have organelles that perform specific metabolic tasks and are supported by a cytoskeleton which runs through the cytoplasm, giving the cell form and shape. In contrast, the more primitive prokaryotic cells are smaller than eukaryotes, and have no nucleus, distinct organelles, or cytoskeleton. 

Components of membrane transformation systems include the nucleus with its DNA, nonhistone chromosomal proteins, and the derived informational molecules (e.g., mRNA) for protein synthesis. The mRNA moves into the cytoplasm through the transformation of membranes. For example, the rough endoplasmic reticulum contains ribosomal RNA with its templates for protein synthesis. The system evolves with cytoplasmic organelles and substrates to influence structure and function. During this process the vacuoles, microtubules, endoplasmic reticulum, subcellular organelles, and plasmalemma may release specific metabolic nitrogenous products (conjugates, enzymes) internally or externally. Some of these may be involves in the biosynthesis of cutin and suberin (76). 

What are the advantages of compartmentalizing particular metabolic pathways within specific organelles ... 

The cytosol is the fluid compartment of the cell and contains the enzymes responsible for cellular metabolism together with free ribosomes concerned with local protein synthesis. In addition to these structures which are common to all cell types, the neuron also contains specific organelles which are unique to the nervous system. For example, the neuronal skeleton is responsible for monitoring the shape of the neuron. This is composed of several fibrous proteins that strengthen the axonal process and provide a structure for the location of specific membrane proteins. The axonal cytoskeleton has been divided into the internal cytoskeleton, which consists of microtubules linked to filaments along the length of the axon, which provides a track for the movement of vesicular material by fast axonal transport, and the cortical cytoskeleton. 

Figure 5.6. Metabolism of proteins by proteases found at the cell surface and internal cellular organelles. Intracellular uptake of proteins often involved receptor-mediated endocytosis initial surface binding can be specific for a hormone (e.g., insulin, glucagon).

A second important difference between mitochondrial and peroxisomal fi oxidation in mammals is in the specificity for fatty acyl-CoAs the peroxisomal system is much more active on very-long-chain fatty acids such as hexacosanoic acid (26 0) and on branched-chain fatty acids such as phytanic acid and pristanic acid (see Fig. 17-17). These less-common fatty acids are obtained in the diet from dairy products, the fat of ruminant animals, meat, and fish. Their catabolism in the peroxisome involves several auxiliary enzymes unique to this organelle. The inability to oxidize these compounds is responsible for several serious human diseases. Individuals with Zellweger syndrome are unable to make peroxisomes and therefore lack all the metabolism unique to that organelle. In X-linked adrenoleukodystrophy (XALD), peroxisomes fail to... 

Enzymes with related functions often are compartmentalized into specific organelles, a process that enhances metabolic efficiency in various ways. First, the higher concentrations of enzymes and intermediates resulting from... 

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