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Lysosomes
| Question | Answer |
|---|---|
| Where are they found? | In all mammalian cells except RBCs |
| What are lysosomes? | Degradative compartments in which macromolecules are hydrolysed into their constituent components |
| Basic Lysosome structure please? | Roughly spherical membrane bound organelles, often with dense, protein-rich cores |
| Other functions of lysosomes? (3) | 1. Role in apoptosis 2. Repairing plasma membrane damage 3. Secretory organelle in immune cells |
| What do hydrolases do? | Break materials down into constituent parts break covalent bonds by hydrolysis |
| How many different lysosomal hydrolases in lysosome lumen? | >45 |
| pH of the lysosome lumen? | 4.5 |
| How is pH of lysosome lumen maintained? | vacuolar proton pump vATPase that pumps H+ into lumen energised by ATP hydrolysis |
| pH of the cytosol? | 7.2 |
| How does the lysosome transport water soluble products of degradation to cytosol? | Transporters in lysosomal membrane |
| Transporters in the lysosomal membrane? | Tend to be secondary active transporters that couple transport of substrate with H+ |
| Ways of delivery of material to lysosomes? (3) | 1. Endocytosis 2. Autophagy 3. Phagocytosis |
| What materials are transported with endocytosis? | Extracellular material & plasma membrane proteins |
| How is extracellular material delivered to the lysosome? | Endocytosis - Taken up non-specifically within vesicles OR bound by receptors on plasma membrane |
| How are plasma membrane proteins delivered to the lysosome? (2 ways) | 1. Endocytosis 2. PM derived vesicles delivery to early endosomes that mature into late endosomes & fuse w/ lysosome to deliver contents |
| Types of autophagy? (3) | 1. Macroautophagy 2. Chaperone mediated autophagy 3. Microautophagy |
| What is macroautophagy? | GET RID OF BIG THINGS FROM CELL - removes old organelles, aggregates of proteins & long-lived proteins |
| Macroautophagy method? (2) | 1. Cytoplasmic contents surrounded by double membrane 2. Autophagosome fuses w/ lysosome delivering cytoplasmic components to lysosome for degradation |
| What is observed of lysosomes in apoptotic cells? | Increased permeability of lysosomal membrane |
| What do cathepsins do? (2) | 1. Cleave proteins at cytosolic pH 2. Trigger mitochondrial/intrinsic pathway of apoptosis via protein Bid |
| How do lysosomes help plasma membrane repair? (2) | 1. Exocytosis of lysosomes to damage site triggered by influx of Ca2+ into cell 2. Ca2+ detected by lysosomal membrane protein synaptotagmin 7 |
| What are lysosomal storage diseases? | Group of >50 genetic disorders w/ defects in degradative lysosome function |
| What are lysosomal storage diseases associated with? | Abnormal accumulation of molecules within lysosomes |
| Examples of Lysosomal Storage Diseases? (4) | 1. I-cell disease 2. Pompe disease 3. Fabry disease 4. ISASD |
| What is I-cell disease? | Mucolipidosis type II - autosomal-recessive disorder - gene mutations in GNPTAB gene |
| Function of GNPTAB gene? | Role in trafficking of lysosomal hydrolases |
| I-cell symptoms? (4) | 1. Formation of intracellular inclusion 2. Facial & skeletal abnormalities 3. Severe mvt impairment & intellectual abilities 4. Heart failure in 1st decade |
| I-cell cure? | NO CURE |
| I-cell molecular basis? | Enzyme affected is involved in modification of M6P tag. Hydrolases not tagged so not recognised by M6P receptors and are secreted by cell |
| Pompe disease cause? | Autosomal recessive mutation in gene encoding lysosomal hydrolase: Lysosomal a-D-glucosidase |
| Pompe disease clinical symptoms? (2) | 1. Progressive cardiac & skeletal myopathy 2. Infantile onset - death within 1st year by cardiorespiratory failure |
| Molecular basis of Pompe disease? | Abnormal accumulation of glycogen in cells: - small % glycogen enters lysosome - Lysosomal a-D-glucosidase cleaves glycogen into glucose to transport to cytosol |
| Pompe disease treatment? (1 + 2) | Enzyme Replacement Therapy 1 .Intravenous infusion of M6P modified enzyme given to patients 2. Enzyme taken up by cell surface M6P & delivered to lysosomes |
| What is Fabry disease? | X-linked disorder resulting from mutations in a-galactosidase |
| Fabry disease clinical symptoms? (3) | 1. Facial abnormalities 2. Wide range of non-specific defects (renal & cardiac problems) 3. Progressive organ & tissue damage |
| What causes the Fabry disease symptoms? | Deposition of glycolipid Gb3 in walls of capillaries and other places |
| Fabry disease molecular mechanisms? | Lack of a-galactosidase = accumulation of Gb3 in lysosomes as a-galactosidase removed terminal galactose from Gb3 |
| Fabry disease treatment? | Enzyme Replacement Therapy (M6P modified form of enzyme) MIGALASTAT - binds to a-D-glucosidase mutants in ER & stabilised so they can traffic to lysosomes |
| What is ISASD? | Infantile sialic acid storage disease (Salla disease) |
| yeah but like WHAT IS ISASD? (like mutation wise) | Autosomal recessive mutations in sialin gene |
| ISASD symptoms? (4) | 1. Facial abnormalities 2. Intellectual disability 3. Enlarged heart, liver & spleen 4. Death within first 2 years of life |
| Salla disease symptoms? (2) | 1. Physical & intellectual impairment 2. Life expectancy 50 yrs |
| What is sialin? | A lysosomal membrane transporter that transports sialic acids from the lysosome to the cytosol |
| Molecular basis of ISASD? | Loss of sialin transport activity results in accumuluation of sialic acids in lysosomes - sialin degraded by ERAD or abolish transport activity |
Created by:
rubyroo
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