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(klok) a device for measuring time.
biological clock  the physiologic mechanism which governs the rhythmic occurrence of certain biochemical, physiologic, and behavioral phenomena in living organisms.


1. An instrument other than a watch for measuring or indicating time, especially a mechanical or electronic device having a numbered dial and moving hands or a digital display.
2. A biological clock.
v. clocked, clocking, clocks
To register or record with a mechanical device: clocked the winds at 60 miles per hour.

clock′er n.


A gene on chromosome 4q12 that encodes a ubiquitously expressed human homolog of the mouse clock gene, which forms a heterodimer with ARNTL and activates E-box element transcription of several circadian clock proteins (e.g., PER1 and PER2). CLOCK is highly expressed in the suprachiasmatic nucleus.

Molecular pathology
CLOCK-ARNTL double mutations in the PAS domains result in syngernistic desensitisation to high levels of CRY on repression of CLOCK-ARNTL transcriptional activity of PER1, disrupting circadian rhythmicity.


A device for measuring time.

biological clock

1. An internal system in organisms that influences behavior in a rhythmic manner. Functions such as growth, feeding, secretion of hormones, the rate of drug action, the wake-sleep cycle, the menstrual cycle, and reproduction coincide with certain external events such as day and night, the tides, and the seasons. Biological clocks appear to be set by environmental conditions in some animals, but if these animals are isolated from their environment they continue to function according to the usual rhythm. A gradual change in environment does produce a gradual change in the timing of the biological clock. See: circadian; maladaptation to night work; zeitgeber
2. A colloquial term for the decrease in fertility that accompanies aging, particularly as women approach the age of 35.

Patient discussion about clock

Q. How do you wake up in the morning if your narcolepsy is so severe you can't hear the alarm clock, phone ring? biggest problem is sleep paralysis, can't wake up. Late for work, everything, life is suffering because of severity. Have tried ritalin, natural supplements, hypnosis therapy, Provigal, antidepressants, nothing seems to work. Employer thinks it's an excuse, friends are irritated, I'm at my wits end. Life is spent sleeping more than awake.

A. Narcolepsy cannot yet be cured. But EDS and cataplexy, the most disabling symptoms of the disorder, can be controlled in most patients with drug treatment. Often the treatment regimen is modified as symptoms change. For decades, doctors have used central nervous system stimulants-amphetamines such as methylphenidate, dextroamphetamine, methamphetamine, and pemoline-to alleviate EDS and reduce the incidence of sleep attacks. For most patients these medications are generally quite effective at reducing daytime drowsiness and improving levels of alertness. However, they are associated with a wide array of undesirable side effects so their use must be carefully monitored. Common side effects include irritability and nervousness, shakiness, disturbances in heart rhythm, stomach upset, nighttime sleep disruption, and anorexia. For full article: Hope this helps.

More discussions about clock
References in periodicals archive ?
In mammals, circadian rhythm is controlled by hypothalamic suprachiasmatic nucleus (SCN), and regulated by a transcriptional feedback loop with clock genes, such as circadian locomotor cycle kaput ( Clock ), Brain and muscle Arnt-like protein-1 ( Bmal1 ), Period ( Per ), Cryptochrome ( Cry ), Reverse erythroblastosis virus ( Rev-erb ), Retinoic acid receptor-related orphan receptor ( Rora ) genes, and their corresponding proteins.
They also indicate that long-term blocking of lunar light by shading or cloud cover, or longterm exposure to extraneous lighting equivalent in strength to a full Moon, can interrupt normal clock gene expression cycles.
Sleep deprivation effects on circadian clock gene expression in the cerebral cortex parallel electroencephalographic differences among mouse strains," Journal of Neuroscience, vol.
Muhlbauer, "Experimental and clinical aspects of melatonin and clock genes in diabetes," Journal of Pineal Research, vol.
In vivo endotoxin synchronizes and suppresses clock gene expression in human peripheral blood leukocytes.
Since Andretic's findings, many researchers have sought to more clearly understand the role of the Clock gene in rhythmicity of drug addiction.
Melatonin, Circadian rythms, and Clock genes in Bipolar Disorder.
Examples of clock genes that have been characterized in humans are hPer (period bomolog)l, hPer2, hPer3, hCLOCK (circadian locomotor output cycles kaput), hCK (casein kinase)1[delta], and hCKl[epsilon].
Feeding cues alter clock gene oscillations and photic responses in the suprachiasmatic nuclei of mice exposed to a light/dark cycle.
Colleen McClung and her team disrupted the Clock gene in mice and they became manic, exhibiting behaviors similar to people with bipolar disorder.
The Clock gene, which controls the body's circadian rhythms, may be integrally involved in the development of bipolar disorder.