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Related Concept Videos

Mitochondrial Membranes01:45

Mitochondrial Membranes

A single mitochondrion is a bean-shaped organelle enclosed by a double-membrane system. The outer membrane of mitochondria is smooth and contains many porins - the integral membrane transporters. Porins enable free diffusion of ions and small uncharged molecules through the outer mitochondrial membrane but limit the transport of molecules larger than 5000 Daltons. Further, the outer mitochondrial membrane forms a unique structure called membrane contact sites with other subcellular organelles,...
The Inner Mitochondrial Membrane01:28

The Inner Mitochondrial Membrane

The inner mitochondrial membrane is the primary site of ATP synthesis. The inner membrane domain that forms a smooth layer adjacent to the outer membrane is called the inner boundary membrane. This domain contains membrane transporters that drive metabolites in and out of the mitochondria.  In contrast, the inner membrane network that invaginates into the matrix space is called the cristae membrane. This domain accounts for principle mitochondrial function as it accommodates the protein...
Translocation of Proteins into the Mitochondria01:19

Translocation of Proteins into the Mitochondria

Mitochondrial precursors are translocated to the internal subcompartments via independent mechanisms involving distinct protein machineries called translocases.
Sorting of outer membrane proteins:
Mitochondrial outer membrane proteins are of two types: the transmembrane, beta-barrel porins, and the membrane-anchored, alpha-helical proteins. Beta-barrel porin precursors are translocated by the TOM complex and inserted into the outer mitochondrial membrane by the SAM complex. In contrast,...
Porin Insertion in the Outer Mitochondrial Membrane01:12

Porin Insertion in the Outer Mitochondrial Membrane

Porins are beta-barrel proteins translocated to the mitochondrial outer membrane through the TOM complex into the intermembrane space. Porin precursors bind TIM chaperones within the intermembrane space and are guided to the Sorting and Assembly Machinery complex or SAM complex on the outer mitochondrial membrane.
Three models describe the assembly of porins by the SAM complex and their insertion into the outer membrane. Model 1 suggests that porins are assembled outside the SAM channel as the...
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...
Mitochondrial Membranes01:45

Mitochondrial Membranes

A single mitochondrion is a bean-shaped organelle enclosed by a double-membrane system. The outer membrane of mitochondria is smooth and contains many porins - the integral membrane transporters. Porins enable free diffusion of ions and small uncharged molecules through the outer mitochondrial membrane but limit the transport of molecules larger than 5000 Daltons. Further, the outer mitochondrial membrane forms a unique structure called membrane contact sites with other subcellular organelles,...

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Related Experiment Video

Updated: May 11, 2026

Inner Mitochondrial Membrane Sensitivity to Na+ Reveals Partially Segmented Functional CoQ Pools
05:27

Inner Mitochondrial Membrane Sensitivity to Na+ Reveals Partially Segmented Functional CoQ Pools

Published on: July 20, 2022

Tim23 links the inner and outer mitochondrial membranes.

M Donzeau1, K Káldi, A Adam

  • 1Institut für Physiologische Chemie der Universität München, Germany.

Cell
|June 1, 2000
PubMed
Summary

Tim23, a mitochondrial protein translocase, spans two membranes, connecting the outer and inner mitochondrial membranes. This novel structure enhances protein import efficiency by facilitating precursor transfer.

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An Improved Method to Isolate Mitochondrial Contact Sites
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Using Live Cell STED Imaging to Visualize Mitochondrial Inner Membrane Ultrastructure in Neuronal Cell Models
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Using Live Cell STED Imaging to Visualize Mitochondrial Inner Membrane Ultrastructure in Neuronal Cell Models

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Related Experiment Videos

Last Updated: May 11, 2026

Inner Mitochondrial Membrane Sensitivity to Na+ Reveals Partially Segmented Functional CoQ Pools
05:27

Inner Mitochondrial Membrane Sensitivity to Na+ Reveals Partially Segmented Functional CoQ Pools

Published on: July 20, 2022

An Improved Method to Isolate Mitochondrial Contact Sites
07:55

An Improved Method to Isolate Mitochondrial Contact Sites

Published on: June 16, 2023

Using Live Cell STED Imaging to Visualize Mitochondrial Inner Membrane Ultrastructure in Neuronal Cell Models
08:48

Using Live Cell STED Imaging to Visualize Mitochondrial Inner Membrane Ultrastructure in Neuronal Cell Models

Published on: June 30, 2023

Area of Science:

  • Mitochondrial biology
  • Membrane protein topology
  • Protein import machinery

Background:

  • Tim23 is a crucial component of the mitochondrial preprotein translocase.
  • It is anchored in the inner mitochondrial membrane with a domain in the intermembrane space.
  • The precise topology and function of Tim23 in coordinating inter-membrane protein transfer were not fully understood.

Purpose of the Study:

  • To elucidate the complete topology of Tim23 within the mitochondrial membranes.
  • To investigate the functional consequences of Tim23's novel membrane-spanning characteristic.
  • To understand how Tim23 integrates the outer and inner mitochondrial membranes.

Main Methods:

  • Biochemical and cell biological approaches were used to determine Tim23 topology.
  • Analysis of protein exposure on the mitochondrial surface.
  • Functional assays to assess protein import efficiency.

Main Results:

  • Tim23 possesses a novel topology, with its N-terminal domain exposed on the outer mitochondrial membrane surface.
  • Tim23 spans both the inner and outer mitochondrial membranes, a previously undescribed characteristic.
  • This dual membrane integration forms direct contacts between the outer and inner mitochondrial membranes.

Conclusions:

  • The unique two-membrane-spanning topology of Tim23 is essential for its function.
  • Tim23 acts as a molecular tether, linking the TOM and TIM23 complexes.
  • This tethering significantly enhances the efficiency of precursor protein transfer and import into mitochondria.