Centromere
The centromere is the constricted region of a chromosome where the two sister chromatids are held together and where the kinetochore assembles to attach the chromosome to the spindle. It is essential for sharing the chromosomes accurately when a cell divides.
The centromere is the constricted region of a chromosome where the two sister chromatids are held together and where the kinetochore assembles to attach the chromosome to the spindle. It is essential for sharing the chromosomes accurately when a cell divides.
Identity: What Defines a Centromere?
In most organisms the centromere is defined less by a particular DNA sequence than by a special histone variant, CENP-A, that replaces histone H3 in some nucleosomes of the region. In humans the DNA consists of long arrays of a 171-base-pair repeat called alpha satellite. The complete sequences of human centromeres were not assembled until 2022.
Function: How Does It Move Chromosomes?
During mitosis and meiosis, protein complexes called kinetochores build on the centromere and grip microtubules of the spindle. The microtubules pull the sister chromatids to opposite poles, and a checkpoint in the cell cycle delays division until every chromosome is attached correctly.
Errors and Variation: What Goes Wrong?
If chromosomes fail to separate properly, daughter cells receive the wrong number, a condition called aneuploidy. Chromosomes are classed by the centromere position: metacentric, submetacentric and acrocentric. A few organisms have holocentric chromosomes whose kinetochores are spread along the whole length.
Centromere at a Glance
| Property | Value |
|---|---|
| Marker | CENP-A histone variant |
| Human DNA | Alpha-satellite repeats of 171 bp |
| Attached by | Kinetochore and spindle microtubules |
See Also
- Chromosomes — the structures it organizes
- Mitosis — the division it guides
- Aneuploidy — the result of segregation errors