Organelles in cells

Lipids occur in cell walls, cellular cytoplasm, and in fat storage cells in animals. In contrast, specialized fat storage cells per se do not exist in plants or seeds. Rather, fatty acids are found in surface waxes that reduce the loss of moisture from leaves, stems, fruits, and seeds of plants in seed cell walls and cytoplasm and as stored triacylglycerols in dispersed spherical organelles in cells of seed embryos (48). 

Rizzuto, R., Marisa, B., Pizzo, P., Murgia, M., and Pozzan, T. (1995). Chimeric green fluorescent protein as a tool for visualizing subcellular organelles in living cells. Curr. Biol. 5 635-642. 

Intracellular motility is also of vital importance in the lives of cells and the organisms they form. Material and organelles are transported within cells along microtubules and microfilaments an extreme example of this are the axons of nerve cells which transport materials to the synapses where they are secreted—another motile event. Other examples of intracellular motility include phagocytosis, pino-cytosis, the separating of chromosomes and cells in cell division, and maintenance of cell polarity. 

The polyamines spermidine and spermine (Figure 31-4) function in cell proliferation and growth, are growth factors for culmred mammalian cells, and stabilize intact cells, subcellular organelles, and membranes. Pharmacologic doses of polyamines are hypothermic... 

These sheet-hke structures are noncovaleiit assemblies that are thermodynamically stable and metabohcaUy active. Numerous proteins are located in membranes, where they carry out specific functions of the organelle, the cell, or the organism. 

Hudon, J. and Muir, A.D., Characterization of the reflective materials and organelles in the bright irides of North American blackbirds (Icterinae), Pigment Cell Res., 9, 96, 1996. 

Most receptors (a notable exception being the steroid receptors that influence DNA transcription) are located on the cell surface, and purified cell membranes are thus an obvious choice of preparation. When a tissue is homogenized, however, any membrane fraction isolated may well contain membranes from intracellular organelles in addition to cell membranes from all the cell types present in the tissue. Thus, brain membranes will contain membranes not only from neurons but... 

Bacteria, being procaryotic, do not show compartmentation of the biosynthetic processes. The genome of a bacterium relates directly to the cytoplasm of the cell. Transcription into mRNA can lead directly to translation, and the processes of transcription and translation are not carried out in separate organelles. Animal cells, being eucaryotic, show compartmentation of the transcription and translation processes. Transcription of the genome into mRNA occurs in the nucleus, whereas translation occurs in the cytoplasm. The messenger RNA in the eucaryote is usually modified by adding to it... 

The eukaryotes these include animals, plants, fungi and protozoa, the DNA of which is enclosed in a membrane-enclosed organelle (the cell nucleus). They have a cytoskeleton (a fine membrane-like network in the interior of the cell, which provides stability) and contain mitochondria. Higher plants, as well as algae, are equipped with chloroplasts for photosynthesis. 

---