Cytoskeleton

Cytoplasmic streaming is the organised flow of the cytoplasm and its constituents within a living cell (Shimmen et al., 2004). Organelles and important molecules move through the cytosol along the structure of the cytoskeleton (actin filaments and microtubules) with the aid of myosin I, an actin-binding motor protein that plays a part in various cell functions including cell motility and endocytosis (Flavell et al., 2008). Actin microfilaments (F-actin) are the thinnest filaments of the cytoskeleton,

Thinner, more darkly stained elastic fibers composed of the protein elastin can also be seen. The principal type of cells seen are lightly-staining fibroblasts that secrete the matrix materials.

Muscle fibres, as shown in Diagram 1, consist of myofibrils, which contain the proteins, actin and myosin, in specific arrangements . The diagram illustrates how a muscle is made up of many fascicles, which in turn are made up of many endomysiums, and within them, many muscle fibres. Each muscle fibre is made up of many myofibrils that consist of sarcomeres bound end on end . Actin is a thin filament, about 7nm in diameter, and myosin is a thick filament, about 15nm in diameter , both of which reside in the sarcomere. They are held together by transverse bands known as Z lines . Diagram 2 shows actin and myosin filaments within a sarcomere, and the Z lines that connect them.

Serves as the cell 's skeleton. It is an interior protein system that gives the cytoplasm quality and adaptability. The cytoskeleton of all cells is made of microfilaments, halfway fibers, and microtubules. Muscle cells contain these cytoskeletal parts in addition to thick fibers. The fibers and microtubules of the cytoskeleton frame a dynamic system whose ceaseless rearrangement influences cell shape and capacity.

Myofibrils are made up of long proteins that include myosin, titin, and actin while other proteins bind them together. These proteins are arranged into thin and thick filaments that are repetitive along the myofibril in sectors known as sarcomeres. The sliding of actin and myosin filaments along each other is when the muscle is contracting. Dark A-bands and light I-bands reappear along myofibrils. The alignment of myofibrils causes an appearance of the cell to look banded or striated. A myofibril is made up of lots of sarcomeres. As the sarcomeres contract individually the muscle cells and myofibrils shorten in length. The longitudinal section of skeletal muscle exhibits a unique pattern of alternating light and dark bands. The dark staining, A-bands possess a pale region in the middle called the H-zone. In the middle of the H-zone the M-line is found, that displays filamentous structures that can join the thick filaments. The light-staining bands also known as I-bands are divided by thin Z-line. These striated patterns appear because of the presence of myofibrils in the sarcoplasm (IUPUI, 2016).

Skeletal Muscle Structure.The cells of skeletal muscles are long fiber-like structures. They contain many nuclei and are subdivided into smaller structures called myofibrils. Myofibrils are composed of 2 kinds of myofilaments. The thin filaments are made of 2 strands of the protein actin and one strand of a regulatory protein coiled together. The thick filaments are staggered arrays of myosin molecules.

1. _Actin__ Th in contractile protein involved in cross-bridge formation, comes in filamentous or globular forms.

Microvilli are small finger-like extensions on the outer surface of the plasma membrane of a cell, they contain microfilaments that connect to the cell’s cytoskeleton. They differ from villi as they are microscopic and are located on the plasma membrane of cells where they increase the surface area for absorption of extracellular materials.

1.a) Contractile protein molecules that are seen in skeletal muscle fibres are actin (thin filaments) and myosin (thick filaments). Together, they produce the force of muscle contractions by forming cross bridges, and moving via a power stroke. The regulatory proteins that are seen within a skeletal muscle are troponin and tropomyosin. These proteins play a role in starting or stopping muscle contractions. When a muscle fibre is relaxed, there are no contractions because actin is unable to bind with the cross bridge. This is because tropomyosin covers the myosin binding sites on the actin proteins. In addition, troponin is not bound to calcium when a muscle fibre is relaxed, thus keeping the tropomyosin in its blocking position. When calcium enters the muscle fibres, it binds with troponin. This binding causes the tropomyosin to move away

There is a fifth flagellum that curves backward along the undulating membrane. There is an accessory filament that runs along the undulating membrane. The costa arises from the kinetosome and the parabasal body lies near the nucleus. An axostyle tube is formed by a sheet of microtubules and has three parts. The anterior portion called the capitulum, the middle part called the trunk, and the posterior regions called the caudal tip. The pelta is made up of microtubules that supports the paraflagellar canal, which is a shallow depression from which all flagella emerge. The trophozoites also contain microbodies also known as the paracostal

The morphology and functions of specialized cells within tissues such as muscle requires the unique organization of the actin cytoskeleton this actin cytoskeleton rely on actin network, vinculin, to locked the filamentous actin (F-actin) to the membrane.1 Vinculin is a structural protein that plays an important role in multiple protein assemblies linking the extracellular matrix to actin cytoskeleton.2 Vinculin is an 116 kDa cytoskeletal protein linked to cell-matrix and cell-cell junctions. It is said to work as one of a few interconnecting proteins required to secure the F-actin to the membrane. Vinculin has a helical head and tail domains attached by a flexible proline-rich linker.3 The head and tail domain mingle in an autoinhibitory manner, blocking binding to a significant number of prospective ligands.4 In addition to vinculin, there is metavinculin (MV), which is a splice variant of vinculin. MV is a muscle-specific splice of vinculin and is expressed in smooth and cardiac muscle tissue. MV is linked to dilated cardiomyopathy (DCM) deficiency which is a form of heart disease.

actin “slid” past each other and neither filament changed in length. In 1957 Allan Huxley

1. Ok so the sliding filament theory is basically the contraction of the sacromere. Calcium released from an ion channel bind to troponin which lies on the thick filament known as the actin. This then causes the tropomyosin to reveal on the actin. The myosin head then releases a phosphate from an ATP which causes then forms a cross bridge attaching both thick and thin filament. Causing one muscle contraction.

Each muscle is made up of several individual muscle fibers bound together by connective tissue. Each muscle fiber contracts individually when stimulated, and each fiber fully contracts or it doesn’t contract at all. The smallest unit of a muscle fiber is a sacromere. Sacromeres are made up of actin and myosin filaments. Each sarcomere contracts and requires energy to do so.

Introduction - Before examining the structural differences between TubZ and the rest of the Tubulin family, it will be necessary to give background on both. Specifically, what Tubulin is and the common characteristics of the Tubulin family, Tubulin’s role in the cell, what TubZ is, what it’s role is, and what similarities it shares with other members of the Tubulin family. A general layout of the paper will also be given at the end of this introduction. General layout would briefly describe the order of the sections to follow.