Sentromeren

Sentromeren, or centromeres in English, are specialized chromosomal regions essential for the accurate segregation of chromosomes during cell division. They serve as the primary assembly site for the kinetochore, a protein complex that attaches chromosomes to spindle microtubules, and they help maintain sister chromatid cohesion until the proper stage of mitosis or meiosis.

Location and structure vary across organisms. In many species, centromeres occupy a defined region near the middle of the chromosome, but their size and DNA composition can differ widely. Centromere identity is largely established epigenetically by the incorporation of the histone H3 variant CENP-A into nucleosomes at the centromere. Surrounding DNA often consists of repetitive sequences known as satellite DNA. Some organisms have regional centromeres that span large intervals, while others are holocentric, with kinetochores forming along nearly the entire chromosome length. Yeasts may possess point centromeres defined by specific DNA elements.

Function and cell-cycle role are central to genome stability. During mitosis and meiosis, kinetochores attach to spindle microtubules, enabling the alignment and segregation of chromosomes. The spindle assembly checkpoint monitors proper attachment and tension to prevent mis-segregation. The cohesin complex holds sister chromatids together until anaphase, when separase activity cleaves cohesin to permit chromatid separation.

Evolutionary and clinical notes indicate centromeres can be highly repetitive and rapidly evolving at the DNA level, while their essential function is preserved through epigenetic specification. Centromere dysfunction can contribute to aneuploidy and is linked to various diseases, including cancer.