Protein turnover refers to_________________

Question

BlackTom AI · Accepted Answer

Protein turnover is the continuous synthesis and degradation of proteins within cells.

1. Relevant knowledge points and concepts
- Proteostasis: the balance of protein synthesis, folding, trafficking, and degradation that maintains cellular function.
- Two major degradation pathways: the ubiquitin–proteasome system (selective removal of damaged/short-lived proteins) and autophagy–lysosome pathway (bulk degradation of long-lived proteins and organelles).
- Protein half-life: different proteins have characteristic turnover rates, allowing dynamic regulation of cellular processes.
- Functional reasons for turnover: quality control (remove damaged/misfolded proteins), regulation of signaling (rapid change in protein levels), and amino acid recycling.

2. Step-by-step reasoning
Step 1: Interpret the phrase “protein turnover” — turnover implies replacement over time, not a one-time event.
Step 2: Compare choices: “folding” is an intramolecular process, “digestion” usually refers to extracellular breakdown of dietary proteins, “synthesis only” omits removal. Only “continuous synthesis and degradation” captures replacement dynamics.
Step 3: Recall mechanisms: newly synthesized proteins are produced by ribosomes while damaged or unneeded proteins are tagged with ubiquitin and degraded by proteasomes or delivered to lysosomes. This simultaneous synthesis and degradation produces a steady-state concentration.

3. Calculations / intermediate steps
- No numeric calculation required. Conceptual intermediate step: Net protein level = synthesis rate − degradation rate; steady-state achieved when rates equal.

4. Why the correct answer is correct
“Continuous synthesis and degradation” exactly expresses that proteins are constantly made and broken down, which is the defining biological meaning of turnover and explains dynamic control over protein populations.

5. Why other options are incorrect
- Protein folding: only one component of protein life cycle, not turnover.
- Protein digestion: typically refers to digestive processes in the gut, not intracellular turnover.
- Protein synthesis only: incomplete, ignores degradation which is essential to turnover.

6. Conclusion
Therefore the correct choice is “Continuous synthesis and degradation,” which matches the provided answer.

Protein turnover refers to_________________单项选择题

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