Histology Wk 5 Flashcards
what are secretory granules
secretory granules are found in cells that store a product until its release by exocytosis is signaled by a metabolic, hor- monal, or neural message (regulated secretion).
The contents of some secretory granules may be up to 200 times more con- centrated than those in the cisternae of the RER.
Secretory granules with dense contents of digestive enzymes are also referred to as zymogen granules.
what are lysosomes
Lysosomes are sites of intracellular digestion and turnover of cellular components.
membrane-limited vesicles that contain about 40 different hydrolytic enzymes and are particularly abundant in cells with great phagocytic activity (eg, macrophages, neutrophils).
acid hydrolyases, phosphatase, phos- pholipases, sulfatases, and β-glucuronidase. As can be seen from this list, lysosomal enzymes are capable of breaking down most macromolecules.
what is the diameter of lysosomes
which are usually spherical, range in diam- eter from 0.05 to 0.5 μm and present a uniformly granular, electron-dense appearance in the TEM
what is the process of endocytosis
Lysosomal hydrolases are synthesized and segregated in the RER and then transferred to the Golgi apparatus, where the enzymes are further modified and packaged in vacuoles that form lysosomes.
The marker mannose-6-phosphate (M6P) is added by a phosphotransferase in the cis Golgi only to the N-linked oligosaccharides of the hydrolases destined for lyso- some.
Membrane receptors for M6P-containing proteins in the trans Golgi network then bind these proteins and divert them from the secretory pathway for segregation into lysosomes.
explain further the process of phagocytosis
Synthesis of lysosomal enzymes occurs in the RER, with packaging in the Golgi apparatus. Endocytosis produces vesicles that fuse with endosomes before merging with lysosomes. Phagocytic vacuoles (or phagosomes) fuse with primary lysosomes to become secondary lysosomes (or heterolysosomes), in which ingested material is degraded. Autophagosomes, such as those depicted here with a mitochondrion in the process of digestion, are formed after nonfunctional or surplus organelles become enclosed with membrane and the resulting structure fuses with a lysosome. The products of lysosomal digestion are recycled to the cytoplasm, but indigestible molecules remain in a membrane-enclosed residual body, which may accumulate in long-lived cells as lipofuscin.
In some cells, such as osteoclasts, the lysosomal enzymes are secreted into a restricted extracellular compartment.
what are proteasomes
not associated with membrane, each approximately the size of the small ribosomal subunit
what are their function
They function to degrade dena- tured or otherwise nonfunctional polypeptides. Proteasomes also remove proteins no longer needed by the cell and provide an important mechanism for restricting the activity of a specific protein to a certain window of time.
how does the proteasome degrade the protein
Ubiquinated proteins are recog- nized by the regulatory particles of proteasomes, unfolded by the ATPase using energy from ATP, and then translocated into the core of the cylindrical structure and degraded by endopeptidases. The ubiquitin molecules are released for reuse and the peptides produced may be broken down further to amino acids or they may have other specialized destinations, such as the antigen-presenting complexes of cells activating an immune response
