Other Eukaryotic Organelles

The structure of the secretory cell is essentially similar to that of other eukaryotic cells. In their normal state, the cells are roughly cubical, c. 10 fim in cross-section. It is estimated that there are c. 5 x 1012 cells in the udder of the lactating cow. A diagrammatic representation of the cell is shown in Figure 1.2d. It contains a large nucleus towards the base of the cell and is surrounded by a cell membrane, the plasmalemma. The cytoplasm contains the usual range of organelles ... 

Comparison of the glyoxylate cycle with the TCA cycle reveals that two of the five reactions of the glyoxylate cycle tire unique to this cycle, whereas the other three reactions are common to both cycles (fig. 13.13). In plant seedlings and many other eukaryotic organisms that possess this capability, the enzymes of the glyoxylate cycle are compartmentalized in specialized organelles called glyoxysomes. 

The endoplasmic reticulum is a eukaryotic organelle with many functions. The outer surface of the structure is often coated with ribosomes undergoing protein synthesis. Proteins to be processed in other ways, such as addition of sugars, are synthesized and transported into the endoplasmic reticulum. Many biological reactions on nonpolar lipid molecules occur in the endoplasmic reticulum. 

A second very important eukaryotic organelle is the mitochondrion, which, like the nucleus, has a double membrane (Figure 1.13). The outer membrane has a fairly smooth surface, but the inner membrane exhibits many folds called cristae. The space within the inner membrane is called the matrix. Oxidation processes that occur in mitochondria yield energy for the cell. Most of the enzymes responsible for these important reactions are associated with the inner mitochondrial membrane. Other enzymes needed for oxidation reactions, as well as DNA that differs from that found in the nucleus, are found in the internal mitochondrial matrix. Mitochondria also contain ribosomes similar to those found in bacteria. Mitochondria are approximately the size of many bacteria, typically about 1 pm in diameter and 2 to 8 pm in length. In theory, they may have arisen from the absorption of aerobic bacteria by larger host cells. 

This conclusion is true not only for our cells and other eukaryotic cells (i.e., sophisticated cells which store their DNA in the special cell organelle called nucleus), but also for more primitive procaryotic cells (which do not... 

In plant cells, as in other eukaryotic cells, the endomembrane system is composed of multiple organelles with distinct morphology and functions. The compartmentalized endomembrane system ensures proper processing and trafficking of macromolecules to the sites of function. A normally functioning endomembrane trafficking machinery is essential for plant growth and development [1]. 

No matter how complex an organism, the cell remains the basic nnit of life. Organisms of interest in this book comprise eukaryotic cells. The plasma membrane fnlflUs two fnnctions it keeps the cell s overall internal environment relatively stable so that the cell can condnct its mnltiple functions and it allows interaction with the variable extracellnlar enviromnent. The additional membranes that snrronnd the cell s nnclens and other intracellnlar organelles create distinct cellnlar compartments with different environmental conditions within the cell s overall environment. These additional membranes effectively create and protect multiple intracellular enviromnents in which different chemical reactions that require different environmental conditions can occur simultaneously (Devlin 2006). 

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