Question

Intermediate filaments are made from elongated fibrous proteins that are assembled into a ropelike structure. Figure Q17-10 shows the structure of an intermediate filament subunit. You are interested in how intermediate filaments are formed, and you create an intermediate filament subunit whose α-helical region is twice as long as that of a normal intermediate filament by duplicating the normal α-helical region while keeping a globular head at the N-terminus and a globular tail at the C-terminus; you call this subunit IFαd. If you were to assemble intermediate filaments using IFαd as the subunit, which of the following predictions describes the most likely outcome?(a) Filaments assembled using IFαd will interact with different cytoskeletal components.

(b) Filaments assembled using IFαd will form dimers that are twice as long as dimers assembled from normal intermediate filaments.
(c) Sixteen tetramers assembled from IFαd will be needed for a ropelike structure to form.
(d) Dimers of IFαd will form by interactions with the N-terminal globular head and the C-terminal globular tail.

Answer 1

The correct answer is option b. The most probable outcome of using an intermediate filament subunit with twice the length of the α-helical region would be the formation of dimers that are twice as long as those formed from normal intermediate filaments.

Step-by-step explanation:

The formation of intermediate filaments involves the polymerization of subunits made from fibrous proteins such as keratin. These subunits have a N-terminal globular head, an α-helical rod-like region, and a C-terminal globular tail. When subjected to a hypothetical modification where the α-helical region is doubled in length as in IFαd subunits, the most likely outcome of filament assembly would be b) Filaments assembled using IFαd will form dimers that are twice as long as dimers assembled from normal intermediate filaments.

This prediction is based on the understanding that the coiled rod region, which would be elongated in IFαd, is responsible for the dimerization of monomers. The structural integrity of intermediate filaments, as well as their function in resisting tension and maintaining cell shape, is sort of 'ropelike' due to the coiling and bundling of these proteins. If the basic dimer length is increased, this would proportionately affect the length of the filaments assembled from these dimers, but the mode of interaction between dimers and the ultimate formation of tetramers or higher-order structures would remain unchanged.