Endoplasmic reticulum ribosomes

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

Electron microscopic examination of midge microsomes prepared by a slightly different procedure than Table VIII revealed a homogeneous mixture of vesicles derived from rough and smooth endoplasmic reticulum, ribosomes and a few mitochondria. Midge preparations are similar in composition to microsomal fractions of southern armyworm fat body and gut (44). 

A bacterial cell may contain about 10,000 such particles. In animal cells as many as 1-10 million ribosomes are found that are usually associated with the internal membranes of the endoplasmic reticulum. Ribosomes can be isolated from other cell components by subjecting tissue extracts in the ultracentrifuge to speeds equivalent to more than 100,000 times gravity. This treatment shows that ribosomes consist of subunits with different sedimentation values (S). Table 6-8 shows some typical values for ribosomes, their component subunits, and associated types of rRNA. The various subunits are associated with varying numbers of different proteins that are believed to be involved in certain aspects of protein synthesis. Bacterial ribosomes may contain up to 37% protein, while plant and animal ribosomes consist of approximately equal amounts of RNA and protein material. 

Ribosomes and microsomes consisting of endoplasmic reticulum, Golgi, and plasma membrane fragments... 

The signal recognition particle (SRP) is a cytosolic ribonucleoprotein complex which binds to signal sequences of nascent membrane and secretory proteins emerging from ribosomes. The SRP consists of a 7S RNA and at least six polypeptide subunits (relative molecular masses 9, 14, 19, 54, 68, and 72 kD). It induces an elongation arrest until the nascent chain/ ribosome/SRP complex reaches the translocon at the endoplasmic reticulum (ER) membrane. 

The membranes of the endoplasmic reticulum contain the enzyme system for acylglycerol synthesis, and the ribosomes are responsible for protein synthesis. 

The life span of the normal red blood cell is 120 days this means that slightly less than 1% of the population of red cells (200 billion cells, or 2 million per second) is replaced daily. The new red cells that appear in the circulation still contain ribosomes and elements of the endoplasmic reticulum. The RNA of the ribosomes can be detected by suitable stains (such as cresyl blue), and cells containing it are termed reticulocytes they normally number about 1% of the total red blood cell count. The life span of the red blood cell can be dramatically shortened in a variety of hemolytic anemias. The number of reticulocytes is markedly increased in these conditions, as the bone marrow attempts to compensate for rapid breakdown of red blood cells by increasing the amount of new, young red cells in the circulation. 

Like other cells, a neuron has a nucleus with genetic DNA, although nerve cells cannot divide (replicate) after maturity, and a prominent nucleolus for ribosome synthesis. There are also mitochondria for energy supply as well as a smooth and a rough endoplasmic reticulum for lipid and protein synthesis, and a Golgi apparatus. These are all in a fluid cytosol (cytoplasm), containing enzymes for cell metabolism and NT synthesis and which is surrounded by a phospholipid plasma membrane, impermeable to ions and water-soluble substances. In order to cross the membrane, substances either have to be very lipid soluble or transported by special carrier proteins. It is also the site for NT receptors and the various ion channels important in the control of neuronal excitability. 

Potter, M. D., and Nicchitta, C. V. (2002). Endoplasmic reticulum-bound ribosomes reside in stable association with the translocon following termination of protein synthesis. J. Biol. Chem. 277, 23314-23320. 

FIGURE 1-5 Detail of the nuclear envelope showing a nuclear pore (single arrow) and the outer leaflet connected to the smooth endoplasmic reticulum (ER) (double arrows). Two cisternae of the rough ER with associated ribosomes are also present. X80,000. 

FIGURE 1 8-3 Intracellular pathway of bioactive peptide biosynthesis, processing and storage. Neuropeptide precursors are synthesized on ribosomes at the endoplasmic reticulum and processed through the Golgi. Axonal transport of the large dense-core vesicle to the synaptic site of release precedes the actual secretion. 

The VMN responds more rapidly and extensively to estradiol (E) than ARC. VMN neurons respond to E within 2h cell body and nuclear diameters are increased nucleolar size increases and rough endoplasmic reticulum and ribosomal RNA increase in the cytoplasm. 

Surprisingly, it turned out that some of peroxisomal membrane proteins are synthesized at the ER, cotranslationally. This seems a unique example that breaks the independence between the free ribosome system and the membrane-bound ribosome system (another example is found in a sorting mechanism into the vacuole). This phenomenon may be interpreted that the peroxisome may originate from the endoplasmic reticulum, evolutionally. 

Ribosomes Ribosomes are organelles that process the cell s genetic instructions to create proteins. These organelles can float freely in the cytoplasm or be connected to the endoplasmic reticulum. 

Endoplasmic Reticulum (ER) A single membrane system of two distinct types, rough and smooth. The rough ER has ribosomes attached to the membrane, whereas the smooth ER does not,... 

The endoplasmic reticulum (ER) consists of iayered membranes surrounding the nucleus. It is invoived in the transport of chemicais throughout the cytopiasm. Rough endoplasmic reticulum is studded with ribosomes, which are the site of protein assembly from mRNA. Smooth ER lacks ribosomes, and provides channeis for transport of moiecuies... 

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