39 Questions
Which of the following is NOT a function of intracellular protein degradation?
Facilitating the synthesis of abnormal proteins
What is the approximate half-life of 'normally' proteins?
100-200 hours
Which type of proteins have a shorter half-life?
Enzymes that catalyze committed steps
In which compartment does lysosomal protein degradation occur?
Lysosomes
What is the pH of lysosomes where protein degradation occurs?
Acidic (pH=4.8)
Which type of proteins are primarily degraded by the cytosol-ubiquitin dependent proteasome system?
Long-lived proteins
What is the half-life of Acetyl CoA carboxylase in a fasted state?
18
Which tissue has the shortest half-life for Lactic Acid Dehydrogenase?
Heart
Which organelles contain digestive enzymes such as lipases, nucleases, and proteases?
Lysosomes
What percentage of protein degradation occurs in the acidified compartment of lysosomes?
10-20%
What is the main process by which vesicles are formed to engulf small amounts of cytoplasm or specific organelles?
Autophagosomes formation
Which nutritional state results in a longer half-life for Acetyl CoA carboxylase?
Fed state
What is responsible for the breakdown of most short-lived proteins in human cells?
Proteosomal degradation
Which protein is tagged by the covalent attachment of ubiquitin for degradation?
Substrate
What is the function of the 19S regulatory particle in the 26S proteasome?
Recognition and binding of polyubiquitinated proteins
What is responsible for the catalysis of the transfer of ubiquitin from E2 to a lysine amino group of the condemned protein?
Enzyme 3 (E3)
What is recycled in the process of proteasomal degradation?
Ubiquitin
Which component is important for the translocation of unfolded proteins into the central core of the proteasome?
19S regulatory particle
What is the critical number of ubiquitin molecules on a target protein for efficient degradation?
4
What is the function of Deubiquitinating enzymes (DUBs)?
Reverse the degradation effects by cleaving the peptide or isopeptide bond between ubiquitin and its substrate protein
Which enzyme family contains relatively small proteins (< 40-kDa)?
UCH (Ubiquitin Carboxyl-terminal Hydrolases)
What is the role of UBP (UBiquitin-specific Processing proteases) gene family?
Reverse the degradation effects by cleaving the peptide or isopeptide bond between ubiquitin and its substrate protein.
What is structurally formed from 7 alpha subunits and 7 beta subunits?
Proteasome 20S core
What is involved in regulation of DNA repair, transcription, and endocytosis?
Ubiquitin
Which organelles contain digestive enzymes such as lipases, nucleases, and proteases?
Lysosomes
What is the pH of lysosomes where protein degradation occurs?
pH=4.8
What is the main process by which vesicles are formed to engulf small amounts of cytoplasm or specific organelles?
Autophagy
Which nutritional state results in a longer half-life for Acetyl CoA carboxylase?
Fed state
What is the critical number of ubiquitin molecules on a target protein for efficient degradation?
Ten ubiquitin molecules
Which component is responsible for the recognition and binding of polyubiquitinated proteins, removal of ubiquitin, unfolding the protein substrate, and translocation into the central core of the proteasome?
19S regulatory particle
What is the critical number of ubiquitin molecules on a target protein for efficient degradation?
Four ubiquitin molecules
What is the function of Deubiquitinating enzymes (DUBs)?
Reversing the degradation effects by cleaving the peptide or isopeptide bond between ubiquitin and its substrate protein
What is the role of UBP (UBiquitin-specific Processing proteases) gene family?
Regulating protein degradation by cleaving ubiquitin from its substrate
What is responsible for the breakdown of most short-lived proteins in human cells?
Proteosomal degradation pathway
Explain the process of protein degradation through ubiquitination and proteasomal degradation. What are the key enzymes and components involved in this process?
Proteins destined for degradation are tagged by the covalent attachment of ubiquitin, followed by degradation by the proteasome. This ubiquitination process involves E1 (ubiquitin activating enzyme), E2 (ubiquitin conjugating enzyme), and E3 (ubiquitin ligase) enzymes. The 26S proteasome, consisting of a 20S core and 19S regulatory particle, is responsible for recognizing and binding polyubiquitinated proteins, removing ubiquitin, unfolding the protein substrate, and translocating it into the central core for degradation.
What is the role of deubiquitinating enzymes (DUBs) in the protein degradation process?
Deubiquitinating enzymes (DUBs) can reverse the degradation effects by cleaving the peptide or isopeptide bond between ubiquitin and its substrate protein. They play a role in regulating the ubiquitination process and can affect protein function.
Describe the structural composition of the 26S proteasome. What are the functions of its core and regulatory particle?
The 26S proteasome consists of a central core (20S) and 19S regulatory particles at either end. The 20S core is formed of 4 rings: the outer rings are formed from 7 alpha subunits and the inner ring is formed from 7 beta subunits. The 19S regulatory particle is important for recognizing and binding polyubiquitinated proteins, removing ubiquitin, unfolding the protein substrate, and translocating it into the central core for degradation.
How is ubiquitin recycled in the process of proteasomal degradation?
Ubiquitin is recycled, not cleaved, during the proteasomal degradation process.
What is the minimum number of ubiquitin molecules required on a target protein for efficient degradation?
A minimum of four ubiquitin molecules on the target protein are critical for efficient degradation of the protein.
Test your knowledge of intracellular protein degradation with this quiz. Learn about the importance of protein turnover and the variation in the half-life of different proteins.
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