Abstract: The living cell is a kind of factory on the microscopic scale, in which an assembly of modular machines carries out, in a spatially and temporally coordinated way, a whole range of activities internal to the cell, including the synthesis of substances essential to its survival, intracellular traffic, waste disposal, and cell division, but also activities related to intercellular communication and exchanges with the outside world, i.e., the ability of the cell to change shape, to move within a tissue, or to organise its own defence against attack by pathogens, injury, and so on. These nanomachines are made up of macromolecular assemblies with varying degrees of complexity, forged by evolution, within which work is done as a result of changes in interactions between proteins, or between proteins and nucleic acids, or between proteins and membrane components. All these cell components measure a few nanometers across, so the mechanical activity of these nanomachines all happens on the nanometric scale. The directional nature of the work carried out by biological nanomachines is associated with a dissipation of energy. As examples of protein assemblies, one could mention the proteasome, which is responsible for the degradation of proteins, and linear molecular motors such as actomyosin, responsible for muscle contraction, the dynein–microtubule system, responsible for flagellar motility, and the kinesin–microtubule system, responsible for transport of vesicles, which transform chemical energy into motion. Nucleic acid–protein assemblies include the ribosome, responsible for synthesising proteins, polymerases, helicases, elongation factors, and the machinery of DNA replication and repair; the mitotic spindle is an integrated system involving several of these activities which drive chromosome segregation. The machinery coupling membranes and proteins includes systems involved in the energy metabolism, such as the ATP synthase rotary motor, signalling cascades, endocytosis and phagocytosis complexes, and also dynamic membrane–cytoskeleton complexes which generate protrusion forces involved in cell adhesion and migration. The ideas of molecular recognition and controlled interfaces between biological components provide the underlying mechanisms for biological machinery and networks [1]. Many proteins illustrate this principle by their modular organisation into domains. The juxtaposition of catalytic domains of known function and domains of interaction with different partners leads to the emergence of new biological functions. It can also create threshold mechanisms, or biological switches, by triggering the activity of a given domain only when several partners interact with the regulatory domains. Many of these interaction domains are well understood. They exist inside different proteins, in particular, in cell signaling networks, and could potentially be used as building blocks in the construction of new proteins.

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   |texte=   Living Nanomachines
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