Signaling control mechanism

They include being a source of energy for translation and other cellular processes, a substrate for RNA polymerase in synthesis of RNA, and a factor bound by G-proteins in cellular signalling/ control mechanisms. GTP is produced by substrate... 

Dry bulb sensors may be bi-metal strips, thermistors or refrigerant-filled phials or bellows responding to pressure differences caused by temperature change. These, in turn, provide an electrical or mechanical signal. The mechanical items are used to alter the value of potentiometers or make-or-break contacts. The signals are transmitted to amplifiers, which respond to the degree of error. An important feature is the proportional band of temperature over which the controls call for up to full plant capacity. 

Dittrich R, Ritter M, Kaps M, Sieber M, Lees K, Lamie V, Nabavi D, Ringelstein E, Markus H, Droste D. The use of embolic signal detection in multicenter trials to evaluate antiplatelet efficacy signal analysis and quality control mechanisms in the CARESS trial. Stroke 2006 37 1065-1069. 

The transmitter is the interface between the process and its control system. The job of the transmitter is to convert the sensor signal (millivolts, mechanical movement, pressure diflerential, etc.) into a control signal (4 to 20 mA, for example). 

Many of the control mechanisms of the cell cycle are of intrinsic nature and are constitutive, i.e., they are operational in every cell cycle and ensure the ordering of the individual steps. However, other control mechanisms exist that are not active in every cell cycle these are only induced when defects are detected in central cell cycle events. These control mechanisms are known as checkpoints. An example of a checkpoint that is only activated when required is the DNA damage checkpoint (see 13.7). This is a biochemical pathway that detects DNA damage and creates a signal that arrests cells in the Gl, S or G2 phase of the cell cycle. 

In addition to the built-in protection and control mechanisms, the cell is also subject to a number of external controls, which ensure that cell division occurs in balance with the overall development of the organism and with external growth conditions. This is a kind of social control of cell division that regulates the progress of the cell cycle, with the help of circulating signal molecules or via cell-cell interactions. 

An oscillating system is formed by the interplay of the three protein classes and the activity of this system makes up the specific biochemical functions of the individual phases of the cycle. The activity of the cychn-dependent protein kinases (CDKs) is central to the oscillating system. These create a signal that initiates downstream biochemical processes and thus determines the individual phases of the cycle. CDK activity is also the starting point for intrinsic and external control mechanisms. 

When mitosis has been completed, the cell requires signals in the form of growth factors to direct towards a new roimd of division. The signals become effective in the first two-thirds of Gi phase. In this time window, the cell is programmed to begin a new cell cycle or to enter Go phase. After a particular point, the restriction point R, no further signals are needed to continue the cell cycle. The cell cycle apparatus is self-contained from this point onwards. S, G2 and M phase occur without external control. The cell cycle may still be halted after crossing the restriction point, however, if the cell detects, via internal control mechanisms or checkpoints, that defects have occurred in the correct course of the phases. 

At present, there is no standard definition of a servomechanism. Some engineers prefer to classify any system with a feedback loop as a servomechanism. According to this interpretation, an electronic amplifier with negative feedback is a servo. More frequently, however, the term servomechanism is reserved for a feedback control system containing a mechanical quantity. Thus, the IRE defines a servomechanism as "a feedback control system in which one or more of the system signals represents mechanical motion . Some would restrict the definition further by applying the term only to a special class of feedback control system in which the output is a mechanical position... 

Historically, the first techniques designed to achieve independet control over pitch or duration were carried out in the time domain Fairbanks, Everitt and Jaeger s modified tape recorder [Fairbanks et al., 1954] probably is the first known automatic time-domain system for speech transposition. By contrast with frequency-domain methods, time-domain techniques for time or pitch scale modification manipulate short-duration time-segments extracted from the original signal, a mechanism usually called sampling or splicing As a result, they tend to require much fewer calculations and lend themselves quite well to real-time implementations. 

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