6/21/2023 0 Comments Er lumen positive charged![]() In some cells there are dilated areas like the sacs of rough endoplasmic reticulum. The Smooth ER consists of tubules and vesicles that branch forming a network. The Smooth ER also contains the enzyme Glucose-6-phosphatase which converts glucose-6-phosphate to glucose, a step in gluconeogenesis. Smooth endoplasmic reticulum is found in a variety of cell types (both animal and plant) and it serves different functions in each. The smooth endoplasmic reticulum has functions in several metabolic processes, including synthesis of lipids, metabolism of carbohydrates and calcium concentration, drug detoxification, and attachment of receptors on cell membrane proteins. N-linked glycosylation: if the protein is properly folded, glycosyltransferase recognizes the AA sequence NX S or NX T (with the S/T residue phosphorylated) and adds a 14 sugar backbone (2 N-acetylglucosamine, 9 branching mannose, and 3 glucose at the end) to the side chain nitrogen of Asn.This is either N-linked or O-linked (O-linked may likely occur in the golgi). initial glycosylation as assembly continues.Rab proteins are key in targeting the membrane, SNAP and SNARE proteins are key in the fusion event. integral membrane proteins that stay imbedded in the membrane as vesicles exit and bind to new membranes.Secreted proteins, either secreted constitutively with no tag, or regulated secretion involving clathrin and paired basic amino acids in the signal peptide.lysosomal enzymes with a Mannose-6-phosphate marker added in the cis-Golgi network.The rough endoplasmic reticulum works in concert with the Golgi complex to target new proteins to their proper destinations. COP II brings vesicles to the golgi and COP I brings the membrane back. Although there is no continuous membrane between the rough ER and the Golgi apparatus, membrane bound vesicles shuttle proteins between these two compartments. The membrane of the rough endoplasmic reticulum is continuous with the outer layer of the nuclear envelope. This makes it easy for the complex to loop the sequence through the hydrophobic membrane. The free ribosome begins producing the polypeptide until a cytosolic signal recognition particle recognizes the pre-piece of 5-15 hydrophobic AAs preceded by a positively charged (basic) amino acid. The ribosomes only bind to the ER once it begins to synthesize a protein destined for sorting. But it should be noted that these ribosomes are not resident of the endoplasmic reticulum initially. The surface of the rough endoplasmic reticulum is studded with protein-manufacturing ribosomes giving it a "rough" appearance (hence its name). The three varieties are called rough endoplasmic reticulum, smooth endoplasmic reticulum, and sarcoplasmic reticulum. The functions of the endoplasmic reticulum vary greatly depending on the exact type of endoplasmic reticulum and the type of cell in which it resides. The phospholipid membrane encloses a space, the cisternal space (or lumen), from the cytosol. The general structure of the endoplasmic reticulum is an extensive membrane network of cisternae (sac-like structures) held together by the cytoskeleton. 1 Nucleus 2 Nuclear pore 3 Rough endoplasmic reticulum (rER) 4 Smooth endoplasmic reticulum (sER) 5 Ribosome on the rough ER 6 Proteins that are transported 7 Transport vesicle 8 Golgi apparatus 9 Cis face of the Golgi apparatus 10 Trans face of the Golgi apparatus 11 Cisternae of the Golgi apparatus ![]()
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