Cell Biology: The Cytoskeleton

The three main classes of the cytoskeleton are microfilaments (composed of actin), intermediate filaments (IFs), and microtubules (MT).

Microtubules act as 'tracks' for the movement of organelles and materials, and also provide a framework for the organization of organelles.

Microfilaments are involved in the growth of axons and also form the force-generating apparatus for cell motility.

<p>Microtubules are hollow tubular structures with 13 protofilaments, composed of alternating a- and b-tubulin subunits, which results in their structural and functional polarity.</p> Signup and view all the answers

<p>MAPs play a role in increasing microtubule stability and promoting the assembly of tubulin subunits, and many are regulated by phosphorylation.</p> Signup and view all the answers

<p>Hyperphosphorylated Tau protein is incapable of binding to microtubules, and is found in neurofibrillary tangles and plaques, which is linked to various forms of dementia.</p> Signup and view all the answers

<p>Microtubules provide structural support and their arrangement determines the overall shape of the cell.</p> Signup and view all the answers

<p>The association with integral membrane proteins, such as cellulose synthase, influences the organization of microtubules by determining the location and orientation of cellulose microfibrils, which in turn determines plant cell shape and growth.</p> Signup and view all the answers

<p>Microfilaments play roles in structural support, cellular motility, intracellular motile processes, and muscle contraction.</p> Signup and view all the answers

<p>Intermediate filaments provide mechanical strength to cells, particularly those that undergo large amounts of stress, such as nerves, muscles, and epithelia.</p> Signup and view all the answers

<p>The basic structure of all intermediate filaments consists of a central α-helical fibrous domain, terminal globular domains of variable size and sequence, and a nonpolar tetramer formed by the anti-parallel association of dimers.</p> Signup and view all the answers

<p>Intermediate filaments grow through end-to-end association and intercalation within existing filaments, and their polymerization and depolymerization are regulated through phosphorylation.</p> Signup and view all the answers

<p>Cytoplasmic intermediate filaments include proteins such as keratin, desmin, and neurofilaments, which are interconnected to other cytoskeletal filaments by plectin crossbridges.</p> Signup and view all the answers

<p>Keratin intermediate filaments are found radiating throughout epithelial cells and often terminate on desmosomes, which are communication points between cells.</p> Signup and view all the answers

<p>Neurofilaments have sidearms that ensure appropriate spacing between parallel fibers, and their structure is unique due to the presence of these sidearms.</p> Signup and view all the answers

<p>Lamins form a strong, mesh-like grid on the nucleoplasmic side of the inner nuclear membrane, called the nuclear lamina, and provide mechanical support to the nucleus.</p> Signup and view all the answers