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Related Concept Videos

Post-translational Translocation of Proteins to the RER01:27

Post-translational Translocation of Proteins to the RER

A sizable fraction of proteins destined for ER are first synthesized in the cell cytosol and then transported across the ER membrane–a process called post-translational translocation. Similar to cotranslationally translocated proteins, these proteins also use the Sec translocon complex to enter the ER lumen.
Targeting proteins to the ER
Hsp40 and Hsp70 chaperone molecules bind the translated proteins in the cytosol to prevent their folding. The chaperone binding helps to keep the signal...
Protein Translocation Machinery on the ER Membrane01:28

Protein Translocation Machinery on the ER Membrane

The translocon complex situated on the ER membrane is the main gateway for the protein secretory pathway. It facilitates the transport of nascent peptides into the ER lumen and their insertion into the ER membrane.
Sec61 protein conducting channel
In eukaryotes, the translocon complex comprises a core heterotrimeric translocator channel called the Sec61 complex. This channel includes three transmembrane proteins, Sec61α, Sec61β, and Sec61γ, and is the largest subunit of the translocon complex.
Overview of Protein Sorting and Transport01:45

Overview of Protein Sorting and Transport

Eukaryotic cells have different membrane-bound organelles with distinct protein requirements. The process by which proteins are targeted to a specific organelle is called protein sorting.
Protein sorting can be of two types: signal-based sorting and vesicle-based trafficking. In signal-based sorting, specific amino acid sequences called sorting signals target proteins to the proper location inside the cell either via gated transport or by protein translocation.  In gated transport, folded...
Cotranslational Protein Translocation01:20

Cotranslational Protein Translocation

Translocation of proteins across membranes is an ancient process that occurs even in bacteria and archaebacteria. In fact, the components of the translocation machinery are still conserved between prokaryotes and eukaryotes.
Sec61 channel partners for cotranslational translocation
During cotranslational translocation, the Sec61 channel partners with the signal recognition particle (SRP), the signal recognition particle receptor (SR), and the ribosomes to transport the nascent polypeptide chain...
Protein Diffusion in the Membrane01:24

Protein Diffusion in the Membrane

Proteins show rotational as well as lateral diffusion across the membrane. The lateral diffusion of proteins was confirmed through the cell fusion experiment where mouse and human cells were fused, resulting in hybrid cells. When the human and mouse cells fused, the specific membrane proteins on human and mouse cells were marked with the red and green-fluorescent markers, respectively. Initially, the red and green fluorescence was located on the respective hemisphere of the cell. As time...
Protein Transport into the Inner Mitochondrial Membrane01:34

Protein Transport into the Inner Mitochondrial Membrane

Nuclear encoded mitochondrial precursors are imported to the inner membrane in a multistep process involving two separate translocons, TIM22 and TIM23. TIM23 is a cation-selective pore that remains closed by the N terminal segment of the protein. Negative charges on the TIM23 act as a receptor for the incoming precursor, pulling the positively charged matrix-targeting sequence for peptide insertion and translocation.
Transport of mitochondrial precursors across the TIM23 channel is driven by...

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Solid-state Graft Copolymer Electrolytes for Lithium Battery Applications
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Solid-state Graft Copolymer Electrolytes for Lithium Battery Applications

Published on: August 12, 2013

Origin of translocation barriers for polyelectrolyte chains.

Rajeev Kumar1, M Muthukumar

  • 1Department of Polymer Science and Engineering, Materials Research Science and Engineering Center, University of Massachusetts, Amherst, Massachusetts 01003, USA.

The Journal of Chemical Physics
|November 26, 2009
PubMed
Summary
This summary is machine-generated.

The free energy barrier for charged macromolecule translocation through a pore is primarily due to conformational changes, not electrostatics. Factors like salt concentration and ionization affect this entropic barrier.

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Assembly and Characterization of Polyelectrolyte Complex Micelles
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Assembly and Characterization of Polyelectrolyte Complex Micelles

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Area of Science:

  • Polymer physics
  • Statistical mechanics
  • Biophysics

Background:

  • Translocating charged macromolecules through nanopores is crucial for applications like DNA sequencing.
  • The initial approach to the pore is hindered by free energy barriers.
  • These barriers arise from complex interactions including electrostatics and conformational entropy.

Purpose of the Study:

  • To evaluate factors contributing to the free energy barrier during the initial stage of single-file polyelectrolyte translocation.
  • To differentiate the roles of conformational entropy and electrostatic interactions in barrier formation.

Main Methods:

  • Utilizing self-consistent field theory for polyelectrolyte behavior.
  • Employing coupled Poisson-Boltzmann equations for ion distribution without radial symmetry.
  • Analyzing contributions to the free energy barrier.

Main Results:

  • The translocation barrier is predominantly entropic, driven by conformational changes of the macromolecule.
  • At moderate to high salt concentrations, the barrier resembles that of uncharged self-avoiding walks.
  • Electrostatic effects slightly increase the free energy barrier.

Conclusions:

  • Conformational entropy is the dominant factor determining the translocation barrier height.
  • Increased ionization, stronger electrostatic interactions, lower salt concentrations, and poorer solvent quality all elevate the barrier.
  • Understanding these barriers is key for controlling translocation processes.