answers: Microfilaments
context: appear to be more closely related to eukaryotes than they are to other prokaryotic bacteria. The current system has the following listed kingdoms in the three domains: Domain Archaea – prokaryotic, no nuclear membrane, distinct biochemistry and RNA markers from bacteria, possess unique ancient evolutionary history for which they are considered some of the oldest species of organisms on Earth; traditionally classified as archaebacteria; often characterized by living in extreme environments. Some examples of archaeal organisms are methanogens which produce the gas methane, halophiles which live in very salty water, and thermoacidophiles which thrive in acidic high temperature water. Domain </s> (triheme), cytochrome "c" (tetraheme), and high-molecular-weight cytochrome "c" (Hmc), cointaining 16 heme groups with only 30-40 residues per heme group. The 3D structures of a number of cyt "c" proteins have been determined. The proteins consist of 4-5 α-helices and 2 β-sheets wrapped around a compact core of four non-parallel hemes, which present a relatively high degree of exposure to the solvent. The overall protein architecture, heme plane orientations and iron-iron distances are highly conserved. Cytochrome "c" proteins containing other prosthetic groups besides heme C, such as flavocytochromes "c" and cytochromes "cd" belong to class IV. An example is the </s> realization that bacteria possess proteins that are homologous to tubulin and actin; the main components of the eukaryotic cytoskeleton. Eukaryotic cells contain three main kinds of cytoskeletal filaments: microfilaments, microtubules, and intermediate filaments. Each cytoskeletal filament type is formed by polymerization of a distinct type of protein subunit and has its own characteristic shape and intracellular distribution. Microfilaments are polymers of the protein actin and are 7 nm in diameter. Microtubules are composed of tubulin and are 25 nm in diameter. Intermediate filaments are composed of various proteins, depending on the type of cell in which they are found; they
question: the smallest of the cytoskeleton elements is the