Biased random walk (biochemistry)
Encyclopedia
In cell biology
, a biased random walk enables bacteria
to search for food and flee from harm. Bacteria propel themselves with the aid of flagella in a process called chemotaxis
, and a typical bacteria trajectory has many characteristics of a random walk
. They move forward for a certain distance, then the course is abruptly altered by a process called tumbling. The average change of direction is about 60°.
The presence of a food supply gradient
adds bias
to the random walk and hence the phrase biased random walk. When the bacterium moves away from an attractant like a food source (sugar) the tumbling frequency increases (tumbling, negative chemotaxis). This makes it possible for the bacterium to change course and head back to the food source. The bacterium is also able to steer away from a repellent such as a toxin by reducing the tumbling frequency (running, positive chemotaxis). The bacterium is able to detect a chemical gradient not by monitoring a difference in concentration in head and tail but rather by a temporal sensing mechanism keeping track of concentration through time and space. The biased random walk in bacterium motility
may be applied in robotic sensor
s that are able to find the source of an oil spill in oceans.
Cell biology
Cell biology is a scientific discipline that studies cells – their physiological properties, their structure, the organelles they contain, interactions with their environment, their life cycle, division and death. This is done both on a microscopic and molecular level...
, a biased random walk enables bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
to search for food and flee from harm. Bacteria propel themselves with the aid of flagella in a process called chemotaxis
Chemotaxis
Chemotaxis is the phenomenon in which somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. This is important for bacteria to find food by swimming towards the highest concentration of food molecules,...
, and a typical bacteria trajectory has many characteristics of a random walk
Random walk
A random walk, sometimes denoted RW, is a mathematical formalisation of a trajectory that consists of taking successive random steps. For example, the path traced by a molecule as it travels in a liquid or a gas, the search path of a foraging animal, the price of a fluctuating stock and the...
. They move forward for a certain distance, then the course is abruptly altered by a process called tumbling. The average change of direction is about 60°.
The presence of a food supply gradient
Gradient
In vector calculus, the gradient of a scalar field is a vector field that points in the direction of the greatest rate of increase of the scalar field, and whose magnitude is the greatest rate of change....
adds bias
Bias
Bias is an inclination to present or hold a partial perspective at the expense of alternatives. Bias can come in many forms.-In judgement and decision making:...
to the random walk and hence the phrase biased random walk. When the bacterium moves away from an attractant like a food source (sugar) the tumbling frequency increases (tumbling, negative chemotaxis). This makes it possible for the bacterium to change course and head back to the food source. The bacterium is also able to steer away from a repellent such as a toxin by reducing the tumbling frequency (running, positive chemotaxis). The bacterium is able to detect a chemical gradient not by monitoring a difference in concentration in head and tail but rather by a temporal sensing mechanism keeping track of concentration through time and space. The biased random walk in bacterium motility
Motility
Motility is a biological term which refers to the ability to move spontaneously and actively, consuming energy in the process. Most animals are motile but the term applies to single-celled and simple multicellular organisms, as well as to some mechanisms of fluid flow in multicellular organs, in...
may be applied in robotic sensor
Sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
s that are able to find the source of an oil spill in oceans.
External links
- Bacterial Chemotaxis Interactive Simulator — A web-app that simulates bacterial chemotaxis using several different algorithms.