Are there any linear, rotary or oscillatory molecular motors in the cells which can have fixed frequeny and which can be used as a reference for elapsed time timer? This question is with relevence to my earlier question 'Is there a realtime molecular clock within the genome to co-ordinate the developmental sequences in an embryo?'


2 Answers 2


There are molecular motors but the frequency is a function of energy input (ATP); similar to the angular velocity dependence on amount of current in electrical motors.

The concept of molecular motor may not be suitable for a clock like device. There are clocks based on genetic circuits, which produce stable oscillations. Examples include the circadian clock, cell division, menstrual cycle etc.

Developmental events involve checkpoints and the timing is regulated by several factors such as number of cells, concentration of some protein etc. However, I haven't come across a master clock that integrates and synchronizes all these signals for precise developmental timing. That makes it an interesting area of research.


These molecular motors' response maybe dynamic and nonlinear. But it entirely dependent on the external influence and also the characteristics of the motor itself including number of active motors involved in operation. As it is microscopic, it will not possible to analyse by assumptions and say they have some random frequency. They do have certain frequency of operation (I do not know whether they are controlled by biological clock or some master clock but they are controlled by nucleus of the cell) and "Modeling molecular motors" explains how motors act on the filament inside the cell. It mainly talks about the influence of external force on the operation of motor and also speed(v) of the motor. The following excerpt from that paper talks about the external force on motor.

The action of the motor is induced by generalized forces, which for the motor/filament system may be identified as the mechanical force fext applied to the motor, and the chemical potential difference Dm, which measures the free-energy change per consumed ‘‘fuel’’ molecule. The force fext describes external forces, for example of optical tweezers, microneedles, or the viscous load of an object that is carried. fext could also include viscous friction forces between the motor and the surrounding solvent if the latter is considered as ‘‘external.’’ The chemical potential difference Dm is for the process of the hydrolysis of Adenosinetriphosphate (ATP) to Adenosinediphosphate(ADP) and phosphate (P). enter image description here

The frequency of molecular motor according to "Biophysics of Molecular Motor" has been classified into two categories:

  1. Density controlled: In the density-controlled model, it is assumed that the depolymerization rate is proportional to the motor density at the terminal site of the microtubule. Here the frequency of motor is dependent on density of the motor.

  2. Flux controlled: Filament depolymerization is determined by the flux of motors to the end. Here the frequency is dependent on the flux of the motor.

In both the above cases the length of the filament on which motor is acting is also important. These models have been analysed and plotted on a graph to give a clear picture of it.

enter image description here

The paper explains the catastrophe frequency, the frequency at which the filament shrinks. Shrinking of of a filament is due to motor. So the paper concludes saying the catastrophe frequency is 0.5 per min for a 8um length of filament.

enter image description here

(Catastrophe = the transition from growing to shrinking of dynamic microtubules).

To summarize, these motors do have speed and frequency of operation but they are not fixed. They vary in a non linear fashion due dynamic environment. But the motor tries to be as much stable and resistant as possible.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .