Subcellular organelle

Question What does a typical animal cell look like  

There is no such thing as a typical animal cell, since cells vary in overall size, shape, and distribution of the various subcellular organelles. Fig. 1-3 is, however, a composite diagram that indicates the relative sizes of the various microbodies. 

The plasma membrane (Fig. 1-4) is the outer boundary of the cell it is a continuous sheet of lipid molecules (Chap. 6) arranged as a molecular bilayer 4-5 nm thick. In it are embedded various proteins that function as enzymes (Chap. 8), structural elements, and molecular pumps and selective channels that allow entry of certain small molecules into and out of the cell, as well as receptors for hormones and cell growth factors (Chap. 6). 

The endoplasmic reticulum (ER) is composed of flattened sacs and tubes of membranous bilayers that extend throughout the cytoplasm enclosing a large intracellular space. The luminal space (Fig. 1-5) is continuous with the outer membrane of the nuclear envelope (Fig. 1-10). It is involved in the synthesis of proteins and their transport to the cytoplasmic membrane (via vesicles, small spherical particles with an outer bilayer membrane). The rough ER (RER) has flattened stacks of membrane that are studded on the outer (cytoplasmic) face with ribosomes (discussed later in this section) that 

What mass fraction of the lipid membranes of a liver cell is plasma membrane  

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The next steps of glucose catabolism are called the citric acid cycle. The pyruvic acid formed in glycolysis is transported into the mitochondria, which arc subcellular organelles with double (inner and outer) membranes. They are referred to as the powerhous-... 

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. 

Mitochondrion A subcellular organelle in which oxidative phosphorylation occurs, leading to the generation of ATP. 

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... 

The biocatalyst is incorporated in different physical forms as an isolated enzyme, a whole cell, a subcellular organelle or a tissue slice depending on... 

The lysosome is the subcellular organelle responsible for physiological turnover of cellular constituents. Their combined incidence is estimated to be 1 8,000 [2]. Knowledge about the molecular and cellular defects has advanced a great deal in recent years. Platt and Walkley [3] have proposed a new classification based on the nature of the molecular defects (Table 41-1). This system will be used here. 

We also demonstrated the induction of apoptosis by PDT mediated by BF4 and by BF6 in CT26 cells at 4-6 h after illumination. The relatively rapid induction of apoptosis after illumination might suggest the fullerenes are localized in subcellular organelles such as mitochondria, as has been previously shown for PS such as benzo-porphyrin derivative (Granville et al., 1998 Gupta et al., 1998 Li et al., 2003). 

Haem synthesis is a good example of a pathway that is partly compartmentalized. The pathway (Figure 5.16) occurs in all cell types for the production of respiratory cytochromes and begins within mitochondria but the majority of the reactions occur in the cytosol cell. Because mature red cells have no subcellular organelles, haem synthesis occurs only in early RBC progenitor cells. Although this is a relatively simple pathway, there are a number of well-known enzyme defects that cause a group of diseases called the porphyrias. 

Fatty acid utilized by muscle may arise from storage triglycerides from either adipose tissue depot or from lipid stores within the muscle itself. Lipolysis of adipose triglyceride in response to hormonal stimulation liberates free fatty acids (see Section 9.6.2) which are transported through the bloodstream to the muscle bound to albumin. Because the enzymes of fatty acid oxidation are located within subcellular organelles (peroxisomes and mitochondria), there is also need for transport of the fatty acid within the muscle cell this is achieved by fatty acid binding proteins (FABPs). Finally, the fatty acid molecules must be translocated across the mitochondrial membranes into the matrix where their catabolism occurs. To achieve this transfer, the fatty acids must first be activated by formation of a coenzyme A derivative, fatty acyl CoA, in a reaction catalysed by acyl CoA synthetase. 

There should be no confusion between Eubacteria and Archaea, though both are unicellular and both lack nuclei and subcellular organelles. In addition to differences in the structures of certain RNA molecules, there are a number of other clear distinctions between the two domains. There are distinct sensitivities to antibiotics. For example, antibiotics such as kanamycin and streptomycin that are effective against a broad spectrum of bacteria have no effect on archaeans. Moreover, the genetic complement of Eubacteria and Archaea are distinct about 30% of all Archaea genes are unique to archaeans. Finally, the lipids that constitute the cell membrane are distinct. There are clear and compelling distinctions between these two great domains of life. 

Eukaryotes are differentiated from the Archaea and Eubacteria by the possession of a nucleus in the cell enclosed by a membrane as well as by membrane-enclosed subcellular organelles. The nucleus houses the basic genetic information of these organisms, their genomes, as I will describe in chapter 14. The eukaryotes are a diverse set of species, including but not limited to all plants and animals. Remarkably, the Archaea are more closely related to Eukarya than they are to the Eubacteria. This reflects a striking origin of the eukaryotic cell. 

All eukaryotic cells possess subcellular organelles known as mitochondria. The central function of the mitochondria, though not the only one, is to produce ATP, the cellular energy currency, coupled to the oxidation of food-derived molecules. 

Mitochondria are subcellular organelles that are energy-generating machines. The electron transport chain is key to ATP generation in mitochondria. 

The measurements can be made at various levels from that of subcellular organelles, to single cells, cell populations and even tissues. They can be made on either fixed cells or on live cells that are incubated under physiological conditions. They can be made in end point assays or kinetically, in real time. Compared to previous manual methods, automation provides a marked improvement in the capacity for sample and experiment throughput, the precision of measurement and in the sheer number and diversity of parameters measureable for an experiment. Consolidation of the technical capabilities allo vs unparalleled vhthin-experiment, cross-comparisons of biochemical, morphological and functional parameters. Compared to flo v cytometry it offers substantially greater analytic capability for morphometric and kinetic parameters, although for substantially lo ver numbers of cells. 

After cell disruption, gross fractionation of the properly stabilized, crude cell homogenate may be achieved by physical methods, specifically centrifugation. Figure 7.11, Chapter 7, outlines the stepwise procedure commonly used to separate subcellular organelles such as nuclei, mitochondria, lysosomes, and microsomes. 

The photosynthetic process in green plants occurs in subcellular organelles called chloroplasts. These organelles resemble mitochondria they have two outer membranes and a folded inner membrane called the thy-lakoid. The apparatus for photosynthesis, including the chlorophyll reaction centers and electron carriers, is in the thylakoid membrane. The chemical reactions of the Calvin cycle take place in the stroma, the region around the thylakoid membrane. 

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