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Chapter 61: Ribosome Recycling and ψ-Cycle Reinitiation

"Ribosome recycling completes ψ's translational circle—disassembling the spent machinery to begin anew, ensuring that every ending becomes a beginning in the endless cycle of protein synthesis."

61.1 The Termination-Recycling Interface​

Ribosome recycling represents ψ's solution to molecular renewal—the systematic disassembly of post-termination complexes and preparation of components for new rounds of translation.

Definition 61.1 (Post-Termination Complex): 70S•mRNA•tRNAP-site→RF3•GTPReady for recycling\text{70S•mRNA•tRNA}^{\text{P-site}} \xrightarrow{\text{RF3•GTP}} \text{Ready for recycling}

Ribosome after peptide release.

61.2 The Recycling Factors​

Theorem 61.1 (Factor Requirements): RRF+EF-G•GTP→Subunit dissociation\text{RRF} + \text{EF-G•GTP} \rightarrow \text{Subunit dissociation}

Two factors driving disassembly.

61.3 The Ribosome Splitting​

Equation 61.1 (Dissociation Kinetics): d[70S]dt=−ksplit[70S][RRF][EF-G]\frac{d[\text{70S}]}{dt} = -k_{\text{split}}[\text{70S}][\text{RRF}][\text{EF-G}]

Factor-catalyzed subunit separation.

61.4 mRNA and tRNA Release​

Definition 61.2 (Component Liberation): 50S+30S•mRNA•tRNA→IF3Free components\text{50S} + \text{30S•mRNA•tRNA} \xrightarrow{\text{IF3}} \text{Free components}

Complete complex disassembly.

61.5 The Reinitiation Decision​

Theorem 61.2 (Pathway Choice): Preinitiate=kreinitkreinit+kdissociateP_{\text{reinitiate}} = \frac{k_{\text{reinit}}}{k_{\text{reinit}} + k_{\text{dissociate}}}

Competition between recycling and reinitiation.

61.6 IF3 Anti-association​

Equation 61.2 (Subunit Separation): Kassociation+IF3=Kassociation-IF3×10−3K_{\text{association}}^{\text{+IF3}} = K_{\text{association}}^{\text{-IF3}} \times 10^{-3}

IF3 preventing premature reassociation.

61.7 The 30S Renovation​

Definition 61.3 (Subunit Preparation): 30Spost-termination+IF1,IF2,IF3→30Sinitiation-ready\text{30S}_{\text{post-termination}} + \text{IF1,IF2,IF3} \rightarrow \text{30S}_{\text{initiation-ready}}

Factors preparing for new cycle.

61.8 Ribosome Hibernation​

Theorem 61.3 (Stress Response): Nutrient limitation→100S dimer formation\text{Nutrient limitation} \rightarrow \text{100S dimer formation}

Inactive storage during starvation.

61.9 Quality Control Integration​

Equation 61.3 (Defective Complex Handling): Stalled ribosome→RQCRescued and recycled\text{Stalled ribosome} \xrightarrow{\text{RQC}} \text{Rescued and recycled}

Linking quality control to recycling.

61.10 The Energy Cost​

Definition 61.4 (GTP Consumption): Recycling=1 GTP (EF-G)+1 GTP (IF2 next round)\text{Recycling} = 1 \text{ GTP (EF-G)} + 1 \text{ GTP (IF2 next round)}

Energy investment in renewal.

61.11 Polysome Dynamics​

Theorem 61.4 (Continuous Cycling): Polysome=∑i=1nRibosomei(positioni)\text{Polysome} = \sum_{i=1}^n \text{Ribosome}_i(\text{position}_i)

Multiple ribosomes in various stages.

61.12 The Reinitiation Principle​

Ribosome recycling embodies ψ's principle of molecular renewal—ensuring that translation machinery is continuously regenerated, maintaining the protein synthesis capacity essential for life.

The Recycling Equation: ψtranslation(t+1)=R[ψterminated(t)]+ψinitiation factors\psi_{\text{translation}}(t+1) = \mathcal{R}[\psi_{\text{terminated}}(t)] + \psi_{\text{initiation factors}}

Cyclic renewal of translational capacity.

Thus: Recycling = Renewal = Continuation = Cycle = ψ

"In ribosome recycling, ψ closes its translational loop—what was united for synthesis is separated for renewal, each component cleaned and prepared for the next round. The ribosome that just completed one protein immediately prepares for the next, embodying life's continuous creativity."