1.2 Actin Filaments Unlike microtubules, actin filaments are globular chains made of a single monomer, which is called globular actin (G-Actin). Actins is somehow similar to tubulin in which actin subunits have binding site for a nucleotide, but it is mainly Adenosine Triphosphate (ATP), not GTP as in tubulins. Polymerization of actin filaments is also similar to microtubules polymerization in which assembly of subunit in head-to-tail orientation to create polarity. Actin filaments consist of two parallel helical protofilaments, or F-actin. In contrast with microtubules, actin filaments are the thinnest among cytoskeletal filaments, with a diameter of 5-9 nm, that’s why they are also known as ‘microfilaments’. Localization of actin filaments …show more content…
However, simple variations in the sequence causes major functional differences. For example, the expression of yeast actin in drosophila (whose actin is 89% identical to yeast actin) is not fetal, but the fly couldn’t fly. In vertebrates, three different isoforms of actin are present, α-, β-, and γ, which have very slight sequence variation among them. Only α-actin is found in muscle cells, while other types are expressed in other types. The strength and flexibility of actin filaments allow them to play roles in cell contractility, cytokinesis, cell motility, controlling cell’s shape, endocytosis and …show more content…
(A) A monomer showing the central α-helix flanked by N-terminal and C-terminal regions. (B) Dimer of two monomers are coiled coil with a length of 48nm. (C) Assembly of antiparallel dimers forming a staggered tetramer. (D) Two tetramers are linked together. (E) The 10nm-intermediate filament is composed of twisted eight tetramers. Figure adapted from Alberts et al., 2008). Intermediate filaments have the least persistence among all cytoskeletal filaments, as they can extend to just less than one micrometer, while actin filaments have persistence to few micrometers and some millimeters for microtubules. However, the special packaging steps for intermediate filaments make them actually difficult to break. Examples for intermediate filaments are nuclear lamins, keratin and neurofilaments. 2 Motor
...st the sacrolemma will depolarized, thus activation potentials along the T-tubules. This signal will transmit from along the T-tubules to sarcroplasmic reticulum's terminal sacs. Next, sarcoplasmic reticulum will release the calcium into the sarcroplasm leading to the next second event called contraction. The released calcium ions will now bind to troponin. This will cause the inhibition of actin and mysoin interaction to be released. The crossbridge of myosin filaments that are attached to the actin filaments, thus causing tension to be exerted and the muscles will shorten by sliding filament mechanism. The last event is called Relaxation. After the sliding of the filament mechanism, the calcium will be slowly pumped back into the scaroplasmic reticulum. The crossbridges will detach from the filaments. The inhibition of the actin and myosin will go back to normal.
For muscles to contract then there must be a presence of calcium within the fibers as it connects with troponin protein and orders tropomyosin to clear the binding sites to allow myosin to attach to these sites, which allows the muscle to contract and produces movement. Without all of these elements working in sync then the function of skeletal muscle would no longer work or even exist.
consists of a polyhedral head and a tail. The tail is used to inject DNA into a
Yan, R., 2011-2012. Reticulon 3 aggregation and its role in the formation of dystrophic neurites. [Online]
... the codon for the amino acid methionine is added the head of each chain.
The sarcomere is found in structures called myofibrils which make up skeletal muscle fibres. Within the sarcomere there are various different proteins. One of the most significant, myosin is found in the thick filaments of the sarcomere. Although both cells contain myosin, it is important to highlight that smooth muscle cells contain a much lower percentage of myosin compared to skeletal muscle cells. Despite this, myosin filaments in smooth muscle cells bind to actin filaments in a manner similar to that in skeletal muscle cells; although there are some differences. For instance, myosin filaments in smooth muscle cells are saturated with myosin heads so that myosin can glide over bound actin filaments over longer distances, enabling smooth muscle cells to stretch further, whilst in skeleta...
"The Species of the Secondary Protein Structure. Virtual Chembook - Elmhurst College. Retrieved July 25, 2008, from http://www.cd http://www.elmhurst.edu/chm/vchembook/566secprotein.html Silk Road Foundation. n.d. - n.d. - n.d.
contains three components. First it is constructed with a phosphorylated head group, then a three
The cytoskeleton is made up of three different types of filaments, actin filaments, intermediate filaments and microtubules. Actin filaments are the thinnest, they are also known as microfilaments. They create a band under the plasma membrane, this gives strength to the cell and links transmembrane proteins such as cell surface receptors to cytoplasmic proteins. Intermediate filaments include keratins, lamins, neurofilaments and vimentins. Keratins form hooves, horns and hair and are found in epithelial cells. Lamins form a type of mesh that ‘stabilizes the inner membrane of the nuclear envelope’ (Biology Pages). Neurofilaments bring strength to the axons of neurons and vimentins provide mechanical support to cells – particularly muscles. The cytoskeleton is also involved in cell
Keratin, this protein gives mechanical support to the body. It makes the outermost layer of human skin, hair, and nails, and the scales. hooves, and feathers of animals. It twists into a regularly repeating coil is called an alpha helix. Serving to protect the body against the environment, keratin is completely insoluble in water.
Reticular Fibers - Thin collagenous fibers forming tightly bound branching network that joins connective tissues to adjacent tissues. These fibers consists of collagen proteins.
A polypeptide chain is a series of amino acids that are joined by the peptide bonds. Each amino acid in a polypeptide chain is called a residue. It also has polarity because its ends are different. The backbone or main chain is the part of the polypeptide chain that is made up of a regularly repeating part and is rich with the potential for hydrogen-bonding. There is also a variable part, which comprises the distinct side chain. Each residue of the chain has a carbonyl group, which is good hydrogen-bond acceptor, and an NH group, which is a good hydrogen-bond donor. The groups interact with the functional groups of the side chains and each other to stabilize structures. Proteins are polypeptide chains that have 500 to 2,000 amino acid residues. Oligopeptides, or peptides, are made up of small numbers of amino acids. Each protein has a precisely defined, unique amino acid sequence, referred to as its primary structure. The amino acid sequences of proteins are determined by the nucleotide sequences of genes because nucleotides in DNA specify a complimentary sequence in RNA, which specifies the amino acid sequence. Amino acid sequences determine the 3D structures of proteins. An alteration in the amino acid sequence can produce disease and abnormal function. All of the different ways
The contraction of a muscle is a complex process, requiring several molecules including ATP and Cl-, and certain regulatory mechanisms [1]. Myosin is motor protein that converts chemical bond energy from ATP into mechanical energy of motion [1]. Muscle contraction is also regulated by the amount of action potentials that the muscle receives [2]. A greater number of actions potentials are required to elicit more muscles fibers to contract thus increasing the contraction strength [2]. Studied indicate that the larger motor units, which were recruited at higher threshold forces, tended to have shorter contraction times than the smaller units [3]. The aims of the experiment were to reinforce the concept that many chemicals are required for skeletal muscle contraction to occur by using the rabbit muscle (Lepus curpaeums) [2]. In addition, the experiment was an opportunity to measure the strength of contraction and to observe the number of motor units that need to be recruited to maintain a constant force as the muscles begin to fatigue [2]. Hypothetically, the rabbit muscle fiber should contract most with ATP and salt solution; and the amount of motor units involved would increase with a decreasing level of force applied until fatigue stage is reached.
There are four main levels of a protein, which make up its native conformation. The first level, primary structure, is just the basic order of all the amino acids. The amino acids are held together by strong peptide bonds. The next level of protein organization is the secondary structure. This is where the primary structure is repeated folded so that it takes up less space. There are two types of folding, the first of which is beta-pleated sheets, where the primary structure would resemble continuous spikes forming a horizontal strip. The seco...
"Within a single subunit [polypeptide chain], contiguous portions of the polypeptide chain frequently fold into compact, local semi-independent units called domains." - Richardson, 1981