biology

Translocase of the inner membrane

Translocase of the inner membrane is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Translocase of the inner membrane rather than just read about it. In short: The translocase of the inner membrane (TIM) is a complex of proteins found in the inner membrane of the mitochondrion. Components of the TIM complex facilitate the translocation of proteins across the inner membrane and into the mitochondrial matrix.

Key takeaways

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Reference excerpt

The translocase of the inner membrane (TIM) is a complex of proteins found in the inner membrane of the mitochondrion. Components of the TIM complex facilitate the translocation of proteins across the inner membrane and into the mitochondrial matrix. They also facilitate the insertion of proteins into the inner mitochondrial membrane, where they must reside in order to function, these mainly include members of the mitochondrial carrier family of proteins.

The TIM23 complex

The TIM23 complex facilitates translocation of matrix-targeted proteins into the mitochondrial matrix. These proteins contain a cleavable presequence. The TIM23 complex is made up of the subunits Tim17, Tim21 and Tim23, which are thought to contribute to the structural formation of the translocation channel that spans the inner membrane, and Tim44, which is a peripheral membrane protein. Tim44 is only weakly associated with Tim23 and is located on the matrix side of the inner membrane. At the opening of the TIM17-23 complex, Tim44 recruits mitochondrial heat shock protein 70, which further mediates translocation of the precursor through ATP hydrolysis. Following protein entry into the matrix, the presequence is cleaved off by the matrix processing peptidase and the protein undergoes folding into an active conformation, facilitated by HSP60.

The TIM22 complex The TIM22 complex is responsible for mediating the integration of carrier preproteins into the inner membrane. Tim22, a subunit of the TIM22 complex, forms a channel within the inner membrane and is referred to as the carrier translocase. Tim54 and the small Tim proteins, Tim9, Tim10 and Tim12 also contribute to the TIM22 complex as well as Tim18. The function of Tim18 is not yet clear; however it is believed to play a role in assembly and stabilisation of the TIM22 complex, although is not involved in protein insertion into the membrane. Tim54, although it does not associate directly with Tim22, is also believed to assist in the stability of Tim22. Unlike cleavable preproteins, following translocation across the outer membrane via the translocase of the outer membrane, carrier preproteins are bound by the soluble Tim9-Tim10 complex of which the majority of this complex (~95%) is free floating within the intermembrane space. It is possible that this small Tim complex is able to stabilise precursor carrier proteins by acting as a chaperone and preventing the hydrophobic precursors from aggregating in the aqueous environment of the intermembrane space. A small portion of Tim9 and Tim10 (~5%) assembles into a modified complex containing Tim12, on the outer surface of the TIM22 complex. Tim12 is membrane bound and thus may act as a linker molecule docking Tim9 and Tim10 to the face of the TIM22 complex. The carrier preprotein is then inserted into the inner mitochondrial membrane in a potential-dependent fashion. The membrane potential is necessary for both insertion of the precursor into the carrier translocase and lateral release of the protein into the lipid phase of the inner mitochondrial membrane, which completes protein translocation. However this membrane potential-dependent process takes place in absence of ATP-driven machinery.

Subfamilies Mitochondrial import inner membrane translocase, subunit TIMM17 InterPro: IPR005678 Mitochondrial import inner membrane translocase, subunit TIMM23 InterPro: IPR005681

Human proteins containing this domain TIM17A; TIMM17A; TIMM17B; TIMM22; TIMM23;

See also Mitochondria outer membrane translocase TIMM17A TIMM22 TIMM23 TIMM44 Sorting and assembly machinery

References

Worked examples

Example 1 — a first encounter with Translocase of the inner membrane

Start with the simplest possible case. Write down what Translocase of the inner membrane claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Translocase of the inner membrane before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Translocase of the inner membrane ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Translocase of the inner membrane

In research: Translocase of the inner membrane appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Translocase of the inner membrane in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Translocase of the inner membrane is common in secondary-school and first-year university syllabi. It links to neighbouring topics Mitochondrial proteins, Protein complexes, Transmembrane proteins, so understanding it makes those chapters shorter.
In everyday life: Look for Translocase of the inner membrane outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Translocase of the inner membrane in 20 minutes

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Frequently asked questions

What is Translocase of the inner membrane in simple terms?

Why does Translocase of the inner membrane matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Translocase of the inner membrane?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Translocase of the inner membrane.