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Lysosome Degradation
Lysosomes, Protein Turnover and Peroxisomes
| Question | Answer |
|---|---|
| Name key features of the lysosome | Has a battery of hydrolases, about 50-60 hydrolases that are capable of degrading polymeric structures |
| True or False: Lysosome cannot remove modifications | False. They remove modifications and take off phosphate groups |
| What can nucleases degrade? Proteases? | Nucleases: Degrade DNA and RNA into bases. Proteases: Degrade proteins into amino acids |
| What pH do nucleases and proteases operate at? | Acidic pH around 5-6 |
| What is the pH in the cytoplasm? | 7.2 |
| Why is the interior of lysosome maintained at an acidic pH? | Because of the active pumping of hydrogen ions at the expense of ATP hydrolysis |
| What do acid phosphatase remove? | Phosphate groups from proteins |
| Where are the hydrolases of the lysosome originally translated? | In the RER by standard pathways |
| Where does N-linked glycosylation occur? | In the ER |
| What are hydrolases glycosylated with? | A mannose sugar from RER and transferred to cis golgi |
| Describe the modification of the mannose sugar on hydrolases | Phosphotransferase puts a precursor sugar on then there is a trimming reaciton and M6P is end product |
| What are M6P receptors recognized by? | By specific M6P receptors and they cluster in a region |
| What do the region of M6P gets coated with? | Clathrin coat |
| What does the coating of clathrin cause? | Results in the pinching off of the coat |
| After the vesicle loses its clathrin coat what happens? | It goes to the endolysosome |
| Describe LAMP proteins | Classic ER-Golgi pathway. Hydrolases within many tissues may have specific tag mechanism whereby there are delivered to the interior |
| What are macrophages? | Specialized for phagocytosis |
| Describe how complements can play a role in phagocytosis | May coat a bacteria and have it specifically recognized by receptors and internalized for cells specific for phagocytosis |
| Describe pinocytosis | Invagination of the plasma membrane. Means drinking of the extracellular fluid (Particle is not concentrated after being taken up) |
| Other endocytosis process are more complex because vesicles can take on tubular shapes and more changes. Describe | pH gets more acidic as they go from plasma membrane becoming more mature lysosomes |
| Can the more complex endocytosis be mediated? | Yes. It can be receptor mediated so that ligand can bind to specific receptors. Receptors can concentrate what is being taken in |
| Describe autophagy | Internal contents of the cell are enclosed by a membrane and will become a lysosome by vesicular fushion |
| Described receptor-mediated endocytosis | A ligand outside binds to receptors and is coated by clathrin. Pinching off of pit and removal of clathrin. Maturation process called elongation |
| Study that lead to receptor mediated endocytosis being worke out | Hypercholesterolemia: Pre-mature aging and defects in LDL receptors |
| Describe microautophagy | Lysosome can undego internalization of membrane. Take in some cellular components consitutively which results in degradation of intracellular soulble proteins |
| Describe Macroautophagy | Resuls in degadation of organelles like mitochondria and vacuoles that form from SER. Forms autophagic vacuoles |
| Describe Direct Protein transfer | Direct uptake of proteins by macroautophagiv vacuoles |
| What induces macroautophagy and direct protein transfer? | Nutritional starvation |
| How is it possible that receptors get degraded along with ligands? | Ubiquitin can cause internalization of the membrane so the receptor is trapped inter-lumenal instead of recycled to PM |
| True or False: Direct protein uptake is chaperone mediated | True. Certain proteins have specific amino acid sequence (signal) |
| True or False: During starvation Direct protein uptake kicks in before macroautophagy | False macroautophay kicks in first then direct protein uptake kicks in for selectivity and can extend for a long period of time |
| Describe lysosomal storage disease | One particular hydrolase is defective or not expressed at all. Accumulation of products in lysosome. (can be fatal) |
| Example of lysosomal storage disease | Tay-Sachs disease (genetic). Develops from absence of Hexosaminidase A. Accumulation of gangliosids |
| Describe the UB-Proteasome system | ATP dependent. Important for tagging proteins that are going to be degraded. Proteasome unwinds the protein so it can fit (Like garbage disposal) |
| True or False: Proteins can be degraded only after translation | False. Can be degraded during translation or after |
| Describe Peroxisomes | Produces hydrogen peroxide. Creates fatty acids and alcohol metabolism. Contribute to cholesterol metabolism. Make myelin |
| What is the role of peroxisomal catalase | Breaks peroxide down to water |
| What is Adrino Leuko Deficiency | Rare disease that results from insufficient myelin synthesis |
| True or False: Peroxisomes are from classic ER-Golgi | False. Thought the membrane may bud off of the ER |
| Where are most proteins of peroxisomes made? | In the cyotsol then translated then imported into peroxisome (signal sequence regulated) |
| What is the 3 amino acid C-terminus of peroximal proteins? | Site that is recognized by a specific transport protein and channels for uptake |
| Waht is Zellwaggers Syndrome | Defect in receptor that recognizes C-terminal tripeptides. Don't get peroxisomes that are properly incorporating their proteins. Can be fatal |
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