Endoplasmic reticulum protein synthesis

Endoplasmic reticulum Protein synthesis, steroid synthesis, glycosylation,... 

Meaden, P., Hill, K., Wagner, J., Slipetz, D., Sommer, S. S., and Bussey, H. (1990). The yeast KRE5 gene encodes a probable endoplasmic reticulum protein required for (l-6)-/ -glucan synthesis and normal growth. Mol. Cell. Biol. 10, 3013-3019. 

Sato, M., Sato, K., Nishikawa, S., Hirata, A., Kato, J., and Nakano, A. (1999). The yeast RER2 gene, identified by endoplasmic reticulum protein localization mutations, encodes aVprenyltransferase, a key enzyme in dolichol synthesis. Mol. Cell Biol. 19, 471-483. 

Fig. 2. Consensus structure of the E. coli 70S ribosome and its subunits. A. B, C and D are different orientations of the large (SOS) subunit E, F, G and H are two orientations of the small (30S) subunit On the large subunit, E, M and P represent the nascent protein exit site, the membrane binding site, and the peptidyl transferase site, respectively. 23S 3 indicates the position of the 3 terminus of 23S rRNA. On the small subunit, IF-1,2,3 represents the probable location of initiation factors 1, 2 and 3. EF-Tu represents the binding site of the EF- Tu GTP aminoacyl-tRNA complex (see Protein biosynthesis). EF-G represents the binding site of elongation factor G (see Protein biosynthesis) near the interface area with the large subunit. 16S 3 and 16S 5 indicate the positions of the 3 and 5 termini of 16S rRNA. Numbers preceded by S and L represent ribosomal proteins of the small and large subunits, respectively, which have been mapped by electron microscopic visualization of subunit-antibody complexes. / is a diagrammatic representation of the whole ribosome, showing the probable location of mRNA and newly synthesized polypeptide, and the position and orientation of the ribosome with respect to the membrane of the endoplasmic reticulum during synthesis of secreted proteins.

Vitamin K A cofactor for the carboxylase of the hepatic endoplasmic reticulum, which is responsible for completing the synthesis of blood-clotting proteins. 

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

Pathways are compartmentalized within the cell. Glycolysis, glycogenesis, glycogenolysis, the pentose phosphate pathway, and fipogenesis occur in the cytosol. The mitochondrion contains the enzymes of the citric acid cycle, P-oxidation of fatty acids, and of oxidative phosphorylation. The endoplasmic reticulum also contains the enzymes for many other processes, including protein synthesis, glycerofipid formation, and dmg metabolism. 

Figure 46-1. Diagrammatic representation of the two branches of protein sorting occurring by synthesis on (1) cytosolic and (2) membrane-bound polyribosomes. The mitochondrial proteins listed are encoded by nuclear genes. Some of the signals used in further sorting of these proteins are listed in Table 46-4. (ER, endoplasmic reticulum GA, Golgi apparatus.)...

The synthesis of the core proteins occurs in the endoplasmic reticulum, and formation of at least some of the above linkages also occurs there. Most of the later steps in the biosynthesis of GAG chains and their subsequent modifications occur in the Golgi apparatus. 

Albumin (69 kDa) is the major protein of human plasma (3.4-4.7 g/dL) and makes up approximately 60% of the total plasma protein. About 40% of albumin is present in the plasma, and the other 60% is present in the extracellular space. The liver produces about 12 g of albumin per day, representing about 25% of total hepatic protein synthesis and half its secreted protein. Albumin is initially synthesized as a preproprotein. Its signal peptide is removed as it passes into the cisternae of the rough endoplasmic reticulum, and a hexapeptide at the resulting amino terminal is subsequently cleaved off farther along the secretory pathway. The synthesis of albumin is depressed in a variety of diseases, particularly those of the liver. The plasma of patients with liver disease often shows a decrease in the ratio of albumin to globulins (decreased albumin-globuhn ratio). The synthesis of albumin decreases rela-... 

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. 

The ion channel receptors are multi-subunit proteins which may be either homomeric (made up of multiple copies of a single type of subunit) or heteromeric (composed of more than one subunit type). These subunits come together after synthesis in the endoplasmic reticulum to form the mature receptor. Notice that stoichiometry is denoted by a subscript number. A receptor composed of two a and three /I subunits is therefore denoted as having a stoichiometry of This can cause confusion when related subunits are given sequential numbers /II, j]2, 3, etc. The convention is therefore that subunits are numbered normally while stoichiometry is indicated by subscripts so that a pentamer of a4 and j33 subunits might have a stoichiometry of a42/133. 

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. 

The site of synthesis of numerous proteins is remote from their site of function. During transfer from one site to the other, proteins must, therefore, cross cellular membranes [43] [44], Proteins are usually synthesized as precursors containing an amino terminal extension, called the signal (leader) peptide, the sequence of which contains the necessary information to guide the protein to and across a specific membrane. After transmembrane transport (called translocation), the signal peptide is cleaved off by specific signal peptidases, which are found in the rough endoplasmic reticulum, and the... 

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