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Chapter 46: Vesicular Transport and ψ-Path Translocation

"In vesicular transport, ψ creates cellular highways—membrane-bound carriers shuttling proteins between compartments, maintaining organization through controlled trafficking."

46.1 The Transport Network​

Vesicular transport represents ψ's solution to intracellular logistics—moving proteins between membrane-bound compartments while maintaining organelle identity and preventing inappropriate mixing.

Definition 46.1 (Transport Routes): ER→COPIIGolgi→ClathrinPM/Endosome\text{ER} \xrightarrow{\text{COPII}} \text{Golgi} \xrightarrow{\text{Clathrin}} \text{PM/Endosome} Golgi→COPIER\text{Golgi} \xrightarrow{\text{COPI}} \text{ER}

Bidirectional trafficking pathways.

46.2 COPII Vesicle Formation​

Theorem 46.1 (Cargo Selection): Sar1-GTP→Sec23/24→Sec13/31→Vesicle\text{Sar1-GTP} \rightarrow \text{Sec23/24} \rightarrow \text{Sec13/31} \rightarrow \text{Vesicle}

Sequential coat assembly capturing cargo.

46.3 Cargo Recognition​

Equation 46.1 (Export Signals): Kdcargo-coat=f(Export signal affinity)K_d^{\text{cargo-coat}} = f(\text{Export signal affinity})

Di-acidic, di-hydrophobic motifs recognized.

46.4 SNARE Machinery​

Definition 46.2 (Fusion Mechanism): v-SNARE+t-SNARE→4-helix bundle\text{v-SNARE} + \text{t-SNARE} \rightarrow \text{4-helix bundle}

Coiled-coil formation driving membrane fusion.

46.5 Rab GTPases​

Theorem 46.2 (Identity Markers): Rab-GDP→GEFRab-GTPmembrane\text{Rab-GDP} \xrightarrow{\text{GEF}} \text{Rab-GTP}_{\text{membrane}}

Compartment-specific small GTPases.

46.6 The Golgi Apparatus​

Equation 46.2 (Cisternal Progression): cis→medial→trans→TGN\text{cis} \rightarrow \text{medial} \rightarrow \text{trans} \rightarrow \text{TGN}

Protein modification during transit.

46.7 Clathrin-Coated Vesicles​

Definition 46.3 (Triskelion Assembly): Clathrin=3 heavy chains+3 light chains\text{Clathrin} = \text{3 heavy chains} + \text{3 light chains} Assembly→Polyhedral cage\text{Assembly} \rightarrow \text{Polyhedral cage}

Self-assembling transport coat.

46.8 Adaptor Proteins​

Theorem 46.3 (Cargo Sorting): AP complex+Sorting signal→Cargo capture\text{AP complex} + \text{Sorting signal} \rightarrow \text{Cargo capture}

Recognition of tyrosine and dileucine motifs.

46.9 Retrograde Transport​

Equation 46.3 (Recycling): kanterograde≈kretrogradek_{\text{anterograde}} \approx k_{\text{retrograde}}

Balanced flow maintaining compartment size.

46.10 Vesicle Uncoating​

Definition 46.4 (Coat Removal): GTP hydrolysis→Coat disassembly→Fusion competence\text{GTP hydrolysis} \rightarrow \text{Coat disassembly} \rightarrow \text{Fusion competence}

Preparing vesicles for fusion.

46.11 Quality Control in Transport​

Theorem 46.4 (Selective Export):

1 \quad \text{if properly folded} \\ 0 \quad \text{if misfolded} \end{cases}$$ Only mature proteins exported. ## 46.12 The Path Principle Vesicular transport embodies ψ's principle of compartmentalized flow—maintaining cellular organization through controlled movement of membrane-bound carriers along defined paths. **The Transport Equation**: $$\psi_{\text{destination}} = \mathcal{V}[\psi_{\text{origin}}] \times \prod_i \text{Checkpoint}_i$$ Vectorial transport with quality checks. Thus: Vesicle = Carrier = Path = Organization = ψ --- *"In vesicular transport, ψ creates order through movement—proteins packaged in membrane bubbles, addressed with molecular tags, delivered to precise destinations. Each vesicle is a cellular package, maintaining compartment identity while enabling communication."*