Flagella, flagellum sperm

Figure 9.30 Flow diagram of the energy chain from food to essential processes in human life. The ATP utilised by the NayK ATPase maintains the ion distribution in nerves that is essential for electrical activity and, in addition, maintains neurotransmitter synthesis, both of which provide communication in the brain and hence consciousness, learning and behaviour (Chapter 14). ATP utilisation by myosin ATPase is essential for movement and physical activity. ATP utilisation by the flagellum of sperm is essential for reproduction and ATP utilisation for synthesis of macromolecules is essential for growth.

In mammals, ciliated cells line the respiratory air passages, the fallopian tubes, and the ventricles of the brain. The cilia beat in a coordinated manner in waves that propel fluids, suspended cells, and small particles along a surface. The motility of the sperm cell is provided by a single flagellum. 

Figure 2. Electron micrograph of cross section of flagellum of mouse sperm, taken near the tip. The axoneme contains nine outer pairs of doublet microtubules and two central singlet microtubules. Several dynein arms and the fibrous sheath of the sperm are also shown.

In spermatozoa, the phosphocreatine shuttle is present to transfer energy from the mitochondria to the flagellum, which is essential for swimming of the sperm (Figure 9.21) (see also Chapter 19). 

Figure 9.21 The creatine/phosphocreatine shuttle in spermatozoa. This shuttle may not be present in all sperm it will depend upon the distance between the mitochondria and the flagellum. Mitochondria are present in the midpiece just below the head. ATP is required for movement of the flagellum which enables the sperm to swim. Dynein ATPase is the specific motor ATPase, similar to myosin ATPase, that transfers energy from ATP to the flagellum. A deficiency of creatine may explain low sperm motility in some infertile men. CK - creatine kinase. Deficiences of enzymes in the pathway for synthesis of creatine are known to occur (see Appendix 8.3).

The midpiece contains the mitochondria which are wrapped around the proximal part of the flagellum. The beating of the flagellum, and hence the swimming of the sperm involves the motor protein known as dynein, which requires ATP hydrolysis. In some species, the diffusion of energy in the spermatozoa is increased by the presence of the creatine/phosphocreatine shuttle (Chapter 9) that is, phosphocreatine and creatine diffuse throughout the cytosol... 

Cilia and flagella are stable microtubule-based structures which project from the plasma membranes of particular eukaryotic cells. The energy-dependent oscillations of these structures can drive material over the surface of a cell or propel the cell along. For example, the whip-like motions of cilia on the cells at the head of the fallopian tube draw newly released ova from the ovaries into and along the oviduct. The snake-like movements of the flagellum on a sperm provide these cells with movement. 

Figure 4. Scheme showing sperm-egg interaction in the abalone. 1. The sperm binds to the egg VE by the plasma membrane at the tip of the AV (AG), (F, flagellum M, mitochondrion N, nucleus). 2. The sperm acrosome reacts releasing lysin and the 18K protein from its anterior tip. 3. Lysin disrupts the fibers of the VE and the 18K coats the extending acrosome process as it extends. 4. The sperm passes through the hole in the VE and the membrane covering the tip of the acrosomal process fuses with the egg (from Vacquier and Lee, 1993). 

The smooth flexible surface of the erythrocyte plasma membrane allows the cell to squeeze through narrow blood capillaries. Some cells have a long, slender extension of the plasma membrane, called a cilium or flagellum, which beats in a whiplike manner. This motion causes fluid to flow across the surface of an epithelium or a sperm cell to swim through the medium. The axons of many neurons are encased by multiple layers of modified plasma membrane called the myelin sheath. This membranous structure is elaborated by... 

A variety of human cells have cilia and flagella, hairlike projections from the surface that have a strokelike motion. These projections contain a flexible organized array of microtubules. Fluid or mucus is propelled over the surface of ciliated epithelial cells by the coordinated beating of cilia. A sperm cell swims by means of a flagellum. 

One of Nature s other motors, this one a microsized motor with recognizable nanoscale components, is the flagellum (see the photograph), the whiplike reversible propeller found on numerous types of bacteria as well as on sperm. The controlled rotation of the flagellum (clockwise or counterclockwise as needed) is one marvel of this motor. During the 1990s researchers synthesized nanoscale rotors that could be started and stopped at will. Most turn both clockwise and counterclockwise unselectively, limiting their utility. 

Property Sperm flagellum (human) Bacterial flagellum ( . coli)... 

Mitochondria of Drosophila sperm form two long strands extending all along the flagellum over the bewilderingjength of more than 15 nun in some species... 

Miyata S, Sato C, Kitamura S, Toriyama M, Kitajima K (2004) A major flagellum sialogly-coprotein in sea urchin sperm contains a novel polysialic acid, an a2,9-linked poly-Al-... 

Application of ideas from polymers has begun to revolutionize bio-related disciplines. Therefore, this review book will not be complete without a chapter detailing such an application. The last chapter ( Modeling the Hydrodynamics of Elastic Filaments and its Application to a Biomimetic Flagellum ) by Stark attempts to model Nature s successful strategies for propulsion such as of sperm cells and fluid transport such as of mucus. The artificial cilium is based on a superparamagnetic filament, actuated by an external magnetic field the latter allows one to explore the filament s capacity to transport fluid. 

In parallel with efforts to identify the AR-inducer in jelly coat, studies have identified a sperm cell surface molecule that binds jelly coat. In preliminary experiments, it was concluded there must be a receptor-like protein on the surface of the acrosome-intact sea urchin sperm, because trypsin treatment of intact sperm blocked induction of the AR by jelly coat. Subsequently the receptor was isolated and shown to be a 210 kDa glycoprotein with the ability to bind jelly coat [16]. A monoclonal antibody to the 210 kDa glycoprotein was shown to induce the AR. Immuno-localization studies showed the 210 kDa glycoprotein was present on the surface of the sperm flagellum, as well as on a thin belt of the membrane surface... 

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