Golgi-endoplasmic reticulum-lysosomes

There may, however, be some reason to attribute the origin of the cell membrane nucleoside diphosphatase to the Golgi apparatus as it is involved in the GERL (Golgi-endoplasmic reticulum-lysosomes) structure... 

Golgi apparatus, endoplasmic reticulum, ribosomes, lysosomes, peroxisomes, and cytoskeleton... 

Transport of proteins and lipids occurs between the organelles of the secretory pathway, i.e. endoplasmic reticulum (ER), Golgi, endosomes, lysosomes and the plasma membrane. 

Figure 46-6. Flow of membrane proteins from the endoplasmic reticulum (ER) to the cell surface. Horizontal arrows denote steps that have been proposed to be signal independent and thus represent bulkflow. The open vertical arrows in the boxes denote retention of proteins that are resident in the membranes of the organelle indicated. The open vertical arrows outside the boxes indicate signal-mediated transport to lysosomes and secretory storage granules. (Reproduced, with permission, from Pfeffer SR, Rothman JE Biosynthetic protein transport and sorting by the endoplasmic reticulum and Golgi. Annu Rev Biochem 1987 56 829.)...

In neurons and non-neuronal cells, kinesin is associated with a variety of MBOs, ranging from synaptic vesicles to mitochondria to lysosomes. In addition to its role in fast axonal transport and related phenomena in non-neuronal cells, kinesin appears to be involved in constitutive cycling of membranes between the Golgi and endoplasmic reticulum. However, kinesin is not associated with all cellular membranes. For example, the nucleus, membranes of the Golgi complex and the plasma membrane all appear to lack kinesin. Kinesin interactions with membranes are thought to involve the light chains and carboxyl termini of heavy chains. However, neither this selectivity nor the molecular basis for binding of kinesin and other motors to membranes is well understood. 

In microorganisms, visualization of the lysosomal system of different species of malaria parasites, (19), the endoplasmic reticulum-Golgi complex system of Tritrichomonas foetus (20) and the Golgi complex and primary lysosomes of Pneumocystis carinii (30) has been attempted using ZIO staining. 

Figure 1.6 Vesicular transport of proteins within the cell. Vesicles from the endoplasmic reticulum [A] carry protein to the Golgi complex, they are repackaged in the Golgi from which they leave to form primary lysosomes [B] or fuse with the plasma membrane this is to add proteins or to be secreted from the cell [C]. In the Golgi, new vesicles are formed to transport the proteins to the plasma membrane (e.g. transport proteins or proteins for export) or the lysosomes. This system transports, safely, dangerous hydrolytic enzyme to the lysosomes and it also protects membrane proteins, or proteins for export, from degradation in the cytosol.

A process similar to endocytosis occurs in the reverse direction when it is known as exocytosis (Figure 5.11). Membrane-bound vesicles in the cytosol fuse with the plasma membrane and release their contents to the outside of the cell. Both endocytosis and exocytosis are manifestations of the widespread phenomenon of vesicular transport, which not only ferries materials in and out of cells but also between organelles, e.g. from the endoplasmic reticulum to the Golgi and then to the lysosomes or to the plasma membrane for secretion (Chapter 1). Many hormones are also secreted in this way, as are neurotransmitters from one nerve into a synaptic junction that joins two nerves (Chapters 12 and 14). 

The most important membranes in animal cells are the plasma membrane, the inner and outer nuclear membranes, the membranes of the endoplasmic reticulum (ER) and the Golgi apparatus, and the inner and outer mitochondrial membranes. Lysosomes, peroxisomes, and various vesicles are also separated from the cytoplasm by membranes. In plants, additional membranes are seen in the plastids and vacuoles. All membranes show polarity—e., there is a difference in the composition of the inner layer (facing toward the cytoplasm) and the outer layer (facing away from it). 

Topical eukaryotic cells (Fig. 1-7) are much larger than prokaryotic cells—commonly 5 to 100 pm in diameter, with cell volumes a thousand to a million times larger than those of bacteria. The distinguishing characteristics of eukaryotes are the nucleus and a variety of membrane-bounded organelles with specific functions mitochondria, endoplasmic reticulum, Golgi complexes, and lysosomes. Plant cells also contain vacuoles and chloroplasts (Fig. 1-7). Also present in the cytoplasm of many cells are granules or droplets containing stored nutrients such as starch and fat. 

Membrane-bounded organelles Absent Mitochondria, chloroplasts (in plants, some algae), endoplasmic reticulum, Golgi complexes, lysosomes (in animals), etc. 

Cellular location of ribosomes In eukaryotic cells, the ribosomes are either "free" in the cytosol or are in close association with the endoplasmic reticulum (which is then known as the "rough" ER or RER). The RER-associated ribosomes are responsible for synthesizing proteins that are to be exported from the cell, as well as those that are destined to become integrated into plasma, ER, or Golgi membranes, or incorporated into lysosomes (see p. 167 loan overview of the latter process). [Note Mitochondria contain their own set of ribosomes and their own unique, circular DNA.]... 

Glycolipids are synthesized in the endoplasmic reticulum and Golgi. They are degraded in the lysosomes by hydrolytic enzymes that sequentially remove groups from the glycolipid in the reverse order from which they were added during synthesis ("last on, first off ). 

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