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Journal of Lipid Research. Abstract Mitochondria are organized as tubular networks in the cell and undergo fission and fusion.
This Article First Published on January 2, doi: Classifications Cell Biology. Services Email this article to a friend Alert me when this article is cited Alert me if a correction is posted Alert me when eletters are published Similar articles in this journal Similar articles in PubMed Download to citation manager Request Permissions. Responses Submit a Letter to the Editor. Google Scholar Articles by Mehta, K. You can learn more about this topic in the related articles below.
The Cell: A Molecular Approach. 2nd edition.
Read More on This Topic. Microtubule s are long filaments formed from 13 to 15 protofilament strands of a globular subunit called tubulin, with the…. Learn More in these related Britannica articles:. Microtubule s are long filaments formed from 13 to 15 protofilament strands of a globular subunit called tubulin, with the strands arranged in the form of a hollow cylinder. Most microtubule plus ends are….
These tubules are made of the same protein as that in the mitotic spindle, the structure to which chromosomes are attached in cell division. There is no immediately obvious selective advantage of the ratio.
zielizuscoha.gq: Cell Structure: Microtubule
Rather, these commonalities indicate that a few functional patterns…. Since even apparently stable microtubular structures have an intrinsic instability, they are considered to be in a dynamic equilibrium , or steady state. Look here to learn about the difference between a steady state and a true equilibrium. To understand the regulation of microtubule assembly and function in any organism is a difficult task. To study microtubules in cells as complex vertebrate e.
The basic mechanisms can be worked out using a much less complex biological model such as a flagellate. For example, the flagella of the photosynthetic protist Chlamydomonas are composed of microtubules, as are all flagella and cilia.
Cilia and flagella have the same basic structure. They are attached to structures known as basal bodies , which in turn are anchored to the cytoplasmic side of the plasma membrane.
From the basal bodies the microtubule "backbone" extends, pushing the plasma membrane out with it. Each of the two central microtubules consists of a single microtubule with 13 protofilaments arranged to form the wall of a circular tube. Each of the outer nine consists of a pair of microtubules that share a common wall see the cross sections of microtubules in the figure. Look at the complete cross section carefully. The hair-like appearance of flagella and cilia in a light microscope is misleading.
The entire structure lies within the cytoplasm of the cell. The treatment given here to the structure of microtubules ignores their true complexity. Functional microtubules include associated proteins, anchoring sites and organizing centers, sites for enzyme activity, etc. In cilia and flagella, tubulin forms a core structure to which other proteins contribute structures called dynein arms, radial spokes, and nexin links.
The arms, spokes, and links hold microtubules together and allow interaction between microtubules that is superficially similar to the sliding of actin and myosin filaments in muscle contraction.
Ciliary and Flagellar Motion One might appreciate the complexity of microtubular organelles by looking at the motion of cilia and flagella. Despite the similarities in structure, the difference in nature of motility by flagella versus cilia is profound, as one can see by comparing representatives of the groups Ciliophora the ciliates and Mastigophora the flagellates. Ciliates and flagellates behave differently, live in different habitats and occupy different niches, and likely represent two different evolutionary lineages.
"Building blocks" of microtubules - tubulins
The main difference in function is in how they are organized. Flagella are much longer than cilia and are usually present singly or in pairs.
A single flagellum may propel the cell with a whip-like motion. A pair of flagella may move in a synchronized manner to pull the organism through the water, in a way similar to the breast stroke of a human swimmer. Cilia tend to cover the surface area of a cell.