Quyết định ngừng hoạt động không dựa trên bất kỳ trình tự DNA chuyên biệt. Các cơ chế bất hoạt X là không rõ ràng nhưng có thể liên quan đến việc đàn áp bởi heterochromation (positioneffect trạng thái khác nhau về màu sắc) hoặc methyl hóa DNA. Quần thể tế bào Clonally bắt nguồn cho thấy một mô hình X-bất hoạt, và điều này được sử dụng cho các xét nghiệm clonality có sẵn. | 588 LYOPHILIZED COAGULATION FACTOR CONCENTRATES The decision to inactivate is not based upon any specific DNA sequence. The mechanism of X inactivation is unclear but may involve repression by heterochromation positioneffect variegation or DNA methylation. Clonally derived cell populations show a single X-inactivation pattern and this is used for many available clonality assays. LYOPHILIZED COAGULATION FACTOR CONCENTRATES See Coagulation factor concentrates. LYSOSOME A membrane-bounded cytoplasmic organelle containing a variety of hydrolytic enzymes that can be released into a phagosome or to the exterior of the cell. Release of lysosomal enzymes in a dead cell leads to autolysis. Early endosomes are located at the periphery of a cell and late endosomes are located in the perinuclear region with the lysosomes between. Lysosomes are composed of membrane and vesicles containing hydrolytic enzymes. Primary lysosomes are small and contain no inclusions secondary lysosomes are larger and contain partially degraded organelles. Secondary lysosomes are phagocytic vesicles with which primary lysosomes have fused. They often contain undigested material. Functioning at a low pH the enzymes are a series of acid hydrolases including proteases to degrade proteins and polypeptides nucleases to degrade RNA and DNA and phosphatases among others. Their function is to mediate in the degradation of senescent membrane components and organelles and to digest endocytosed foreign material within the cell. Following contact with bacteria they form phagosomes. Lysosomal Storage Diseases339 Although the first description of a lysosomal storage disorder was that of Tay-Sachs disease in 1881 the lysosome was not discovered until 1955 by Christian De Duve. The first demonstration by Hers in 1963 of a link between an enzyme deficiency and a storage disorder Pompe s disease paved the way for a series of seminal discoveries about the intracellular biology of these enzymes and their substrates
