14 Oscillations, Rhythms and Synchronized Time Bases …
231
40 min ultradian clock in the yeast, Saccharomyces cerevisiae, like circadian clocks
and physical clocks, are temperature compensated, exhibiting a Q 10 close to 1.
The term “the Biological Clock”, as often used, refers to the ~24 h period circadian
clock that has evolved in almost all animals, plants, and many fungi and cyanobacteria
[50, 141]. It matches many hundreds of biochemical, physiological and behavioral
functions to the daily rotation of the earth. Circadian rhythms are comparatively
recent innovations on the evolutionary time scale [85, 94, 163]. Although crucially
important, especially in biomedical understanding and applications, they are not
fundamental core characteristics of the living state: they represent the icing on the
cake. Many unicellular organisms (e.g., yeasts, [86] with no ‘canonical’ circadian
receptors or genes’ can entrain to daily environmental cycles.
14.1.6 Ultradian (Circahoralian) Clocks
Clocks or timekeepers that cycle many times in a day are called ultradian (a general
term), or more specifically circahoralian (~hourly ones) [11]. In baker’s or brewer’s
yeasts e.g., some defined strains of Saccharomyces cerevisiae, a 40 min rhythm is a
basic timer mechanism, closely linked to cycles of mitochondrial energization [15,
101, 102]. In another yeast (with a faster growth rate), this timekeeper is of shorter
duration e.g., in Candida utilis it is 30 min [64], Lloyd et al. [93, 99], whereas in
Schizosaccharomyces pombe longer, at 60 min [90, 135–137]. Longer period oscillations have been repeatedly described in yeasts or bacteria in continuous cultures in
the earlier literature: these may stem from perturbative disturbances. Klevecz [69] has
measured the mammalian quantal increments in cultured cell division times as being
about 4 h. Brodsky [10, 12] has surveys showing circahoralian rhythms measured
by different characteristics in a diverse range of cells, and tissues from animals as
30–80 min. Ultradian rhythms are extensively studied in plants (stem growth, leaf
movements, etc. [103].
14.1.7 The Cell-Division Cycle
The cell-division cycle is not a clock but an emergent biological process hypothetically composed of multiple oscillators, check- points ‘sizer’ and temporal controls
[48, 75, 85, 91, 94, 95, 97, 104]. It is often regarded as depending on a series
of stepwise progressions, i.e., like a set of dominoes that must fall in a specific
sequence, controlled at specific “checkpoints”. Eukaryotes have evolved prior to the
cyclin/cyclin kinase mechanism, and respiratory oscillations are sufficient to trigger
and progress the cell division cycle [133]. Many other investigators have always
regarded the cell cycle (and it is now evident) to be a complex process dependent on
231
40 min ultradian clock in the yeast, Saccharomyces cerevisiae, like circadian clocks
and physical clocks, are temperature compensated, exhibiting a Q 10 close to 1.
The term “the Biological Clock”, as often used, refers to the ~24 h period circadian
clock that has evolved in almost all animals, plants, and many fungi and cyanobacteria
[50, 141]. It matches many hundreds of biochemical, physiological and behavioral
functions to the daily rotation of the earth. Circadian rhythms are comparatively
recent innovations on the evolutionary time scale [85, 94, 163]. Although crucially
important, especially in biomedical understanding and applications, they are not
fundamental core characteristics of the living state: they represent the icing on the
cake. Many unicellular organisms (e.g., yeasts, [86] with no ‘canonical’ circadian
receptors or genes’ can entrain to daily environmental cycles.
14.1.6 Ultradian (Circahoralian) Clocks
Clocks or timekeepers that cycle many times in a day are called ultradian (a general
term), or more specifically circahoralian (~hourly ones) [11]. In baker’s or brewer’s
yeasts e.g., some defined strains of Saccharomyces cerevisiae, a 40 min rhythm is a
basic timer mechanism, closely linked to cycles of mitochondrial energization [15,
101, 102]. In another yeast (with a faster growth rate), this timekeeper is of shorter
duration e.g., in Candida utilis it is 30 min [64], Lloyd et al. [93, 99], whereas in
Schizosaccharomyces pombe longer, at 60 min [90, 135–137]. Longer period oscillations have been repeatedly described in yeasts or bacteria in continuous cultures in
the earlier literature: these may stem from perturbative disturbances. Klevecz [69] has
measured the mammalian quantal increments in cultured cell division times as being
about 4 h. Brodsky [10, 12] has surveys showing circahoralian rhythms measured
by different characteristics in a diverse range of cells, and tissues from animals as
30–80 min. Ultradian rhythms are extensively studied in plants (stem growth, leaf
movements, etc. [103].
14.1.7 The Cell-Division Cycle
The cell-division cycle is not a clock but an emergent biological process hypothetically composed of multiple oscillators, check- points ‘sizer’ and temporal controls
[48, 75, 85, 91, 94, 95, 97, 104]. It is often regarded as depending on a series
of stepwise progressions, i.e., like a set of dominoes that must fall in a specific
sequence, controlled at specific “checkpoints”. Eukaryotes have evolved prior to the
cyclin/cyclin kinase mechanism, and respiratory oscillations are sufficient to trigger
and progress the cell division cycle [133]. Many other investigators have always
regarded the cell cycle (and it is now evident) to be a complex process dependent on