Centromere
Say it: SEN-truh-meer
A centromere is the constricted region of a chromosome where its two sister chromatids are held together and where spindle fibers attach in cell division.
Also: centromeres, primary constriction
Definition
What is a centromere?
The centromere is the narrow waist of a chromosome, seen as a pinched point in pictures of condensed chromosomes and often called the primary constriction. After DNA is copied, each chromosome consists of two identical sister chromatids, and the centromere is where they stay most firmly joined until division pulls them apart.
During mitosis and meiosis, a protein structure called the kinetochore assembles at each centromere, and microtubules of the spindle attach to it. In mitosis, once the cohesin proteins holding the sisters together are cut at anaphase, these microtubules drag one chromatid of each pair toward each pole of the cell, so both daughter cells receive a full set. Centromeres usually sit on long stretches of repeated DNA, in humans a repeat called alpha satellite DNA, but the site is marked mainly by a special variant of histone H3 rather than by the sequence alone.
The position of the centromere shapes chromosomes in a karyotype: metacentric chromosomes have it near the middle, submetacentric ones off center and acrocentric ones close to one end. When centromeres or kinetochores fail, nondisjunction can leave daughter cells with the wrong number of chromosomes. The centromere should not be confused with the centrosome, which organizes the spindle microtubules.
Word parts
Where does the word “centromere” come from?
- centro-
- center, sharp pointGreek kentron
- -mere
- partGreek meros
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Terms that go with it
- ChromosomeA chromosome is a thread-like structure of DNA and protein that carries an organism's genes; most human cells hold 46 of them in 23 pairs.
- MitosisMitosis is the division of a cell's nucleus that gives each of two daughter cells an identical, complete set of chromosomes.
- MeiosisMeiosis is a two-stage cell division that turns one diploid cell into four genetically different haploid cells, the precursors of eggs and sperm.
- KaryotypeA karyotype is the full set of chromosomes in a cell, or a picture of them sorted into pairs, used to check chromosome number and structure.
- NondisjunctionNondisjunction is the failure of paired chromosomes or sister chromatids to separate in cell division, leaving cells with the wrong chromosome number.
- MicrotubuleA microtubule is a hollow tube built from the protein tubulin, one of the main cytoskeleton fibers, used for cell shape, transport and cell division.
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Checked against
Written for biofideX in plain words, after checking these references:
- NHGRI Talking Glossary: Centromere
- OpenStax Biology 2e, 10.2 The Cell Cycle
- OpenStax Anatomy and Physiology 2e, 3.5 Cell Growth and Division
- NCBI MeSH: Centromere
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