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Lysosomes (1)

Lysosomes are the recycling system of the cell. They are small membrane-limited vesicles that contain 50-60 hydrolytic enzymes that are most active around pH 5. They take up old mitochondria, membrane, ribosomes, peroxisomes, lots of things like bacteria that come from outside the cell, individual cytosolic proteins, and they dismember them into their monomeric components. Proteins are broken down to amino acids, polysaccharides to simple sugars, lipids to fatty acids and glycerol, and nucleic acids to nucleosides. Sulfate and phosphate are hydrolyzed from sugars and proteins. These monomeric subunits then escape into the cytoplasm through specific transporter channels and can be reused by the cell to synthesize new macromolecules. Lysosomal recycling is the ultimate response to starvation, and permits a cell to destroy certain components in order to replace and repair others essential for survival.

Several different methods are used for substrates to enter lysosomes.

(1) fusion with an endosome.

(2) fusion with a phagosome.

(3) entry of some proteins through the membrane.

(4) If digestion of a cellular organelle is to occur, a unique mechanism utilizes the use of membrane segments of the RER. By unknown stimuli, double membrane segments of RER membrane without ribosomes surround and engulf organelles like mitochondria and peroxisomes. The resulting structure has a double outer membrane, and is named an autophagosome. Digestion of the contents of the autophagosome follow its fusion with a lysosome. The lifetime of an autophagosome is only 4-8 minutes, and as a result they are seldom observed in electron micrographs of normal cells.Image

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Learn to code

Codecademy is the easiest way to learn how to code. It’s interactive, fun, and you can do it with your friends.

http://www.codecademy.com/

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Proprioception

 
Proprioception (play /ˌprpri.ɵˈsɛpʃən/ PRO-pree-o-SEP-shən), from Latin proprius, meaning “one’s own” and perception, is the sense of the relative position of neighbouring parts of the body and strength of effort being employed in movement.[1] It is distinguished from exteroception, by which we perceive the outside world, and interoception, by which we perceive pain, hunger, etc., and the movement of internal organs.

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