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NBME 20 Answers

nbme20/Block 2/Question#22

A 44-year-old woman comes to the physician for a ...

Ubiquitin ligase

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From Amboss on Protein Degradation:

"Endogenous proteins are degraded by proteasomes. Exogenous proteins are degraded by lysosomes"

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submitted by hayayah(525),

In eukaryotic cells, two major pathways—the ubiquitin-proteasome pathway and lysosomal proteolysis—mediate protein degradation.

The major pathway of selective protein degradation in eukaryotic cells uses ubiquitin as a marker that targets cytosolic and nuclear proteins for rapid proteolysis.

The other major pathway of protein degradation in eukaryotic cells involves the uptake of proteins by lysosomes and digestion by proteases.

missi199  Could I ask why it is not Lysosomal protease +4  
smc213  "Certain viruses have evolved to recruit the cellular E3 ligases to induce the degradation of cellular proteins that might have harmful effects on the viral life cycle. For instance, the protein E6 of Human papillomavirus (HPV) recruits the cellular E3 ubiquitin ligase E6-AP to induce ubiquitination and degradation of p53, thereby allowing viral replication." from: https://www.mdpi.com/1999-4915/9/11/322/htm +1  
smc213  USMLE Kaplan: A majority of cellular proteins are degraded via the ubiquitin proteasome pathway, including many proteins that play a role in maintaining cellular homeostasis. These include proteins that regulate the cell cycle, apoptosis, etc. +2