cleaved
Meaning of cleaved: A shape rather than an event: the cell was never cut, and the folded outline is simply what a pathologist reports seeing.
Definition of cleaved
Cleaved describes a cell nucleus that looks split, folded or grooved rather than smoothly rounded when viewed under a microscope. The appearance comes from deep indentations in the membrane around the nucleus. The same word carries a second, unrelated use in laboratory science, where a molecule is said to be cleaved when an enzyme cuts it into pieces at a particular point.
What does a cleaved nucleus look like?
A normal lymphocyte has a round or slightly oval nucleus with a smooth outline. A cleaved one has a linear groove running into it, sometimes deep enough that the nucleus appears folded in half or split into lobes. Nothing has actually been divided. The membrane is indented, and the indentation shows as a pale line under a light microscope. The distinction is made at high magnification on a stained slide, and it is a judgement about shape rather than a measurement.
Why did the appearance matter?
It was one of the features used to sort lymphomas before genetic and antibody-based methods existed. An older classification divided these tumors by cell size and by whether the nuclei were cleaved, producing categories with names such as small cleaved cell lymphoma. Those names still appear in older records and in some textbooks. Current classifications identify the same tumors by the cell they arise from and by their genetic changes, so the appearance is now one observation among many rather than the basis of the name.
What does cleaved mean applied to a molecule?
| Usage | Meaning |
|---|---|
| Cleaved nucleus | A folded or grooved outline seen down the microscope |
| Cleaved protein | A protein cut by an enzyme, often in order to activate it |
| Cleaved DNA | A strand cut at a defined sequence |
The second sense is the more common in laboratory reports. Many proteins are built in an inactive form and only work once a section has been cut away, and antibodies recognizing only the cut version are used to show that a process such as programmed cell death has been switched on.
Also known as
Used in a sentence
The smear showed a population of small cells with cleaved nuclei.
Good to know
Nothing is physically divided in a cleaved cell; the word records an indented nuclear outline, and the older lymphoma names built on it have been replaced by classifications based on cell origin and genetics.