page_title: Chromosome
section_title: Metaphase chromatin and division
hierarchical_section_title: Chromosome / Eukaryotes / Metaphase chromatin and division
caption_attribution_description: Čeština: Metafázní chromosomy lidského (ženského) lymfocytu, barveno Chromomycinem A3 Deutsch: Metaphasechromosomen aus einer weiblichen menschlichen Lymphozytenzelle, gefärbt mit Chromomycin A3, fluoreszenzmikroskopische Aufnahme. Hergestellung: Colcemid-Behandlung, Hypotonie, Methanol-Eisessig Fixierung, Auftropfen, Lufttrocknen, Färbung. English: Metaphase chromosomes from a female human lymphocyte, stained with Chromomycin A3, fluorescence microscopy. Made with: Colcemid treatment, hypotonic shock, methanol acetic acid fixation, dropping, air drying, staining.
context_page_description: A chromosome is a DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins which, aided by chaperone proteins, bind to and condense the DNA molecule to prevent it from becoming an unmanageable tangle. This three-dimensional genome structure plays a significant role in transcriptional regulation.
  Chromosomes are normally visible under a light microscope only when the cell is undergoing the metaphase of cell division. Before this happens, every chromosome is copied once, and the copy is joined to the original by a centromere, resulting either in an X-shaped structure if the centromere is located in the middle of the chromosome or a two-arm structure if the centromere is located near one of the ends. The original chromosome and the copy are now called sister chromatids. During metaphase the X-shape structure is called a metaphase chromosome. In this highly condensed form chromosomes are easiest to distinguish and study. In animal cells, chromosomes reach their highest compaction level in anaphase during chromosome segregation.
context_section_description: In the early stages of mitosis or meiosis (cell division), the chromatin double helix become more and more condensed. They cease to function as accessible genetic material (transcription stops) and become a compact transportable form. The loops of 30-nm chromatin fibers are thought to fold upon themselves further to form the compact metaphase chromosomes of mitotic cells. The DNA is thus condense about 10,000 folds. Chromosome scaffold play important role to hold the chromatin into compact chromosome. Loops of 30 nm structure further condense with scaffold, into higher order structures. Chromosome scaffold is made of proteins including condensin, topoisomerase IIα  and kinesin family member 4 (KIF4) .  This highly compact form makes the individual chromosomes visible, and they form the classic four arm structure, a pair of sister chromatids attached to each other at the centromere. The shorter arms are called p arms (from the French petit, small) and the longer arms are called q arms (q follows p in the Latin alphabet; q-g "grande"; alternatively it is sometimes said q is short for queue meaning tail in French). This is the only natural context in which individual chromosomes are visible with an optical microscope.
  Mitotic metaphase chromosomes are best described by a linearly organized longitudinally compressed array of consecutive chromatin loops.
  During mitosis, microtubules grow from centrosomes located at opposite ends of the cell and also attach to the centromere at specialized structures called kinetochores, one of which is present on each sister chromatid. A special DNA base sequence in the region of the kinetochores provides, along with special proteins, longer-lasting attachment in this region. The microtubules then pull the chromatids apart toward the centrosomes, so that each daughter cell inherits one set of chromatids. Once the cells have divided, the chromatids are uncoiled and DNA can again be transcribed. In spite of their appearance, chromosomes are structurally highly condensed, which enables these giant DNA structures to be contained within a cell nucleus.
caption: Human chromosomes during metaphase
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