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trans-Golgi Network: A network of membrane compartments, located at the cytoplasmic side of the Golgi apparatus, where proteins and lipids are sorted for transport to various locations in the cell or cell membrane.

Golgi Apparatus

JoVE 10970

As they leave the Endoplasmic Reticulum (ER), properly folded and assembled proteins are selectively packaged into vesicles. These vesicles are transported by microtubule-based motor proteins and fuse together to form vesicular tubular clusters, subsequently arriving at the Golgi apparatus, a eukaryotic endomembrane organelle that often has a distinctive ribbon-like appearance.

The Golgi apparatus is a major sorting and dispatch station for the products of the ER. Newly arriving vesicles enter the cis face of the Golgi—the side facing the ER—and are transported through a collection of pancake-shaped, membrane-enclosed cisternae. Each cisterna contains unique compositions of enzymes and performs specific protein modifications. As proteins progress through the cis Golgi network, some are phosphorylated and undergo removal of certain carbohydrate modifications that were added in the ER. Proteins then move through the medial cisterna, where they may be glycosylated to form glycoproteins. After modification in the trans cisterna, proteins are given tags that define their cellular destination. Depending on the molecular tags, proteins are packaged into vesicles and trafficked to particular cellular locations, including the lysosome and plasma membrane. Specific markers on the membranes of these vesicles allow them to dock

 Core: Cell Structure and Function

Exocytosis

JoVE 10711

Exocytosis is used to release material from cells. Like other bulk transport mechanisms, exocytosis requires energy.

While endocytosis takes particles into the cell, exocytosis removes them. Sometimes, the released material are signaling molecules. For example, neurons typically use exocytosis to release neurotransmitters. Cells also use exocytosis to insert proteins, such as ion channels, into their cell membranes, secrete proteins for use in the extracellular matrix, or release waste. There are two main types of exocytosis in eukaryotes: regulated and non-regulated (or constitutive). Regulated exocytosis, which requires an external signal, is used to release neurotransmitters and secrete hormones. Unlike regulated exocytosis, constitutive exocytosis is carried out by all cells. Cells use constitutive exocytosis to release components of the extracellular matrix or incorporate proteins into the plasma membrane. There are five major steps in regulated exocytosis and four in constitutive exocytosis. The first step is vesicle trafficking, in which vesicles transport material to the plasma membrane. Motor proteins actively move vesicles along cytoskeletal tracks of microtubules and filaments. The second step is vesicle tethering, in which vesicles are linked to the plasma membrane. In the third step, vesicle docking, the vesicle membrane at

 Core: Membranes and Cellular Transport

Initial Evaluation of Antibody-conjugates Modified with Viral-derived Peptides for Increasing Cellular Accumulation and Improving Tumor Targeting

1Department of Nuclear Medicine and Radiobiology, Université de Sherbrooke, 2Sherbrooke Molecular Imaging Center (CIMS), Université de Sherbrooke, 3Sherbrooke Institute of Pharmacology

JoVE 55440

 Bioengineering
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