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1005 Lysosomes Peroxisomes Dr Lowrie
UC MED 2015 1005 Lysosomes Peroxisomes Dr Lowrie
28
Medical
Graduate
10/10/2011

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Term
early endosomes
Definition
membrane-enclosed compartments associated with endocytotic pathways. They are restricted to a portion of the cytoplasm near the cell membrane where vesicles originating from the cell membrane fuse. It has a slightly more acidic environment (pH 6.2 to 6.5) than the cytoplasm.
Term
late endosomes
Definition
Late endosomes are found near the Golgi and nucleus. They are more acidic, usually pH 5.5
Term
how substances are transported between the early and late endosomes
Definition
via multivesicular bodies
Term
role of M6P and its receptor in sorting to peroxisome
Definition
M6P is added to the surface of prohydrolase enzymes and acts as a target for M6P receptor. M6P receptors are found in early and late endosomes, lysosomes and the Golgi. The Golgi sends the prohydrolases to endosomes. The acidic environment of the late endosomes causes the release of prohydrolases from the M6P receptors.
Term
why are late endosomes called pre-lysosomes
Definition
because they can turn into lysosomes
Term
how do early endosomes sort proteins
Definition
sort proteins that have been internalized by endocytosis via localized changes in pH
Term
Compartment of Uncoupling Receptor and Ligands (CURLs)
Definition
Another word for early endosome
Term
contents and function of lysosomes
Definition
Lysosomes are digestive organelles that are rich in hydrolytic enzymes, such as proteases, nucleases, glycosidases, lipases and phospholipases. They have a unique membrane that is resistant to hydrolytic digestion.
Term
differences between primary and secondary lysosomes in function and EM
Definition
primary lysosomes are newly formed and and are only solid color in EM. Secondary lysosomes occur when primary lysosomes swallow a substance to be hydrolyzed and have dark clumps within them on EM
Term
chloroquine
Definition
kills malarial parasites by raising the pH of lysosomes, inactivating many lysosomal enzymes, which interferes with digestive processes
Term
Constitutive secretory pathway of targeting lysosomal membrane proteins to lysosome
Definition
lysosomal integral membrane proteins exit the Golgi in coated vesicles and are delivered to the cell surface. Here, they are endocytosed and, via early and late endosomes, reach the lysosomes
Term
Golgi-derived coated vesicle pathway of targeting lysosomal membrane proteins to lysosome
Definition
the membrane proteins exit the Golgi in clathrin-coated vesicles. They travel and fuse with late endosomes
Term
why lysosomal membrane proteins are not digested by lysosomal enzymes.
Definition
because sugar molecules cover almost the entire luminal surface of these proteins. This protects them from digestion.
Term
names of the three pathways for delivery of substances to lysosome for digestion
Definition
using phagosome, using receptor-mediated endocytosis or pinocytosis, autophagy
Term
delivery of substances to the lysosome for digestion using phagosomes
Definition
Extracellular large particles are phagocytosed. A phagosome, with the material internalized within the cytoplasm, receives hydrolytic enzymes to become a late endosome, which matures into a lysosome
Term
delivery of substances to lysosome for digestion using pinocytosis or receptor-mediated endocytosis
Definition
Small extracellular particles are internalized by pinocytosis and receptor-mediated endocytosis. They follow the endocytotic pathway through early and late endosomal compartments and are finally degraded in lysosomes
Term
delivery of substances to lysosome for digestion using macroautophagy
Definition
In macroautophagy, a portion of the cytoplasm or an entire organelle is first surrounded by a double or multilamellar intracellular membrane of ER to form a vacuole called an autophagosome. After delivery of lysosomal enzymes, the autophagosome matures into a lysosome. The isolation membrane disintegrates within the hydrolytic compartment of the lysosome.
Term
delivery of substances to lysosome for digestion using microautophagy
Definition
In microphagy, cytoplasmic proteins are degraded in a slow, continuous process under normal physiologic conditions. Small cytoplasmic soluble proteins are internalized into lysosomes by invagination of the lysosomal membrane.
Term
List two cell types that secrete lysosomal contents into the extracellular space
Definition
Osteoclasts and neutrophils release lysosomal enzymes directly into the extracellular space to digest components of the extracellular matrix.
Term
Lysosomal storage diseases
Definition
Lysosomal storage diseases are caused by the absence of certain lysosomal enzymes, which causes the patholoic accumulation of undigested substrate in residual bodies.
Term
Appearance and function of peroxisomes
Definition
Peroxisomes are single spherical, membrane-bound organelles. They contain oxidative enzymes. Catalase present in peroxisomes breaks down hydrogen peroxide. Peroxisomes also are responsible for β–oxidation of fatty acids. Peroxisomes in hepatocytes convert alcohol to acetaldehyde.
Term
Explain what is produced by the oxidation that occurs in peroxisomes. Name the enzyme in peroxisomes that breaks down the substance produced by oxidation
Definition
Hydrogen peroxide is produced in most oxidation reactions and is broken down by catalase in peroxisomes.
Term
Generation and targeting of peroxisomal enzymes
Definition
Peroxisomal enzymes are synthesized on cytoplasmic ribosomes and are imported into the peroxisome via peroxisomal targeting signal (Ser-Lys-Leu) attached to its carboxy-terminus
Term
Zellweger syndrome
Definition
Zellweger syndrome is when peroxisomes lose their ability to function because of a lack of necessary enzymes. It is caused by a mutation in the gene encoding the receptor for peroxisome targeting signal so that it does not recognize the signal Ser-Lys-Leu at the carboxy terminus of enzymes directed to peroxisomes
Term
Lipofuscin granules
Definition
Lipofuscin is a brownish-gold pigment visible in H&E staining that accumulates during the years as a result of aging. It is a conglomerate of oxidized lipids, phospholipids, metals and organic molecules
Term
Hemosiderin
Definition
Hemosiderin is an iron-storage complex found in the cytoplasm. It is visible in light microscopy as a deep brown granule and is basically indistinguishable from lipfuscin.
Term
glycogen
Definition
Glycogen is a branched polymer used as the storage material for glucose. It is not stained in H&E, but can be seen by PAS and also appears in EM as clusters of granules that occupy significant portions of the cytoplasm.
Term
lipid droplets
Definition
droplets are usually extracted by organic solvents used to prepare tissue for EM and light microscopy. Fat droplets in light microscopy are actually holes in the cytoplasm wehere the lipid had been extracted.
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