Bacterial motion

Bacterial motion is generally associated with the presence of organs of locomotion known as flagella (singular, flagellum). They were first observed in stained preparations by Cohn. The presence of flagella does not mean necessarily that the organisms are always motile, but it indicates a potential power to move. 

Independent bacterial motion is a true movement of translation and must be distinguished from the quivering or back-and-forth motion exhibited by very small particles suspended in a liquid. This latter type of motion is called Brownian movement and is caused by the bombardment of the bacteria by the molecules of the suspending fluid. 

Figure 34.33. Charting a Course. This projection of the track of an E. coli bacterium was obtained with a microscope that automatically follows bacterial motion in three dimensions. The points show the locations of the bacterium at 80-ms intervals. [After H. C. Berg. Nature 254(1975) 390.]...

A Rotary Motor Drives Bacterial Motion (Text Section 54.4)... 

Proteins can be broadly classified into fibrous and globular. Many fibrous proteins serve a stmctural role (11). CC-Keratin has been described. Fibroin, the primary protein in silk, has -sheets packed one on top of another. CoUagen, found in connective tissue, has a triple-hehcal stmcture. Other fibrous proteins have a motile function. Skeletal muscle fibers are made up of thick filaments consisting of the protein myosin, and thin filaments consisting of actin, troponin, and tropomyosin. Muscle contraction is achieved when these filaments sHde past each other. Microtubules and flagellin are proteins responsible for the motion of ciUa and bacterial dageUa. 

Lipids also undergo rapid lateral motion in membranes. A typical phospholipid can diffuse laterally in a membrane at a linear rate of several microns per second. At that rate, a phospholipid could travel from one end of a bacterial ceil to the other in less than a second or traverse a typical animal ceil in a few minutes. On the other hand, transverse movement of lipids (or proteins) from one face of the bilayer to the other is much slower (and much less likely). For example, it can take as long as several days for half the phospholipids in a bilayer vesicle to flip from one side of the bilayer to the other. 

The whole body movement of bacterial cells uses flagella motors which drive a peculiar motion of runs and rotations. In this fumbling manner they follow vaguely external gradients of attractants such as sources of food, light or magnetic fields, and they move in the opposite sense in a repellent chemical gradient by chemotaxis. 

Some authors have described the time evolution of the system by more general methods than time-dependent perturbation theory. For example, War-shel and co-workers have attempted to calculate the evolution of the function /(r, Q, t) defined by Eq. (3) by a semi-classical method [44, 96] the probability for the system to occupy state v]/, is obtained by considering the fluctuations of the energy gap between and 11, which are induced by the trajectories of all the atoms of the system. These trajectories are generated through molecular dynamics models based on classical equations of motion. This method was in particular applied to simulate the kinetics of the primary electron transfer process in the bacterial reaction center [97]. Mikkelsen and Ratner have recently proposed a very different approach to the electron transfer problem, in which the time evolution of the system is described by a time-dependent statistical density operator [98, 99]. 

Two examples where actin polymerization is observed in eukaryotes are in the bacterial pathogens Listeria monocytogenes and Shigella flexneri. The motion that the eukaryote pathogens exhibit is the actin based motility in the cytoplasm of their host. Actin polymerization is known to occur via an insertion polymerization mechanism. The movement is a result of site-directed tread-milling of the actin filaments. This type of movement is classified as a propulsive type motion. The driving force for actin pol)unerization as well as the next motor is the conversion of adenosine triphosphate (ATP) to adenosine diphosphate (ADP). ... 

All of the molecules are in motion. Due to constant collisions, however, they do not advance in a straight path but move in zigzags. Due to their large mass, proteins are particularly slow. However, they do cover an average of 5 nm in 1 ms—a distance approximately equal to their own length. Statistically, a protein is capable of reaching any point in a bacterial cell in less than a second. 

The mechanochemical rotatory motion of bacterial flagella, driven by electrochemical proton gradients across the peripheral membrane. Each complete turn requires... 

Detailed review of the structures that underlie proton-driven rotary motion of ATP synthase and bacterial flagella. 

There is probably no biological phenomenon that has excited more interest among biochemists than the movement caused by the contractile fibers of muscles. Unlike the motion of bacterial flagella, the movement of muscle is directly dependent on the hydrolysis of ATP as its source of energy. Several types of muscle exist within our bodies. Striated (striped) skeletal muscles act under voluntary control. Closely related are the involuntary striated heart muscles, while smooth involuntary muscles constitute a third type. Further distinctions are made between fast-twitch and slow-twitch fibers. Fast-twitch fibers have short isometric contraction times, high maximal velocities for shortening, and high rates of ATP hydrolysis. 

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