Centromere Topics

• spindle fibers
• sister chromatids
• metaphase stage
• chromosome breakage
• dna sequences
• satellite dna
• alpha satellite
• cell nucleus
• centromeres
• spindle apparatus
• kinetochores
• anaphase
• constriction
• yeasts
• chromosomes
• proteins
• organisms
• cen
• bp

Related Images

Source

del.icio.us Tags

• chromosome
• dna
• genetics

Centromere, Centromere

These sequences bind specific proteins called "cen"-Proteins. During mitosis the centromeres can be identified in particular during the metaphase stage as a constriction at the chromosome. At this centromeric constriction the two mostly identical halves of the chromosome, the sister chromatids, are held together until late metaphase. During mitotic division, a transient structure called kinetochore is formed on top of the centromeres. The kinetochores are the sites where the spindle fibers attach. Kinetochores and the spindle apparatus are responsible for the movement of the two sister chromatids to opposite poles of dividing cell nucleus during anaphase. Usually the mitosis is immediately followed by a cell division cytokinesis. However, mitosis and cytokinesis are separate processes and can be uncoupled.

DNA sequences are both necessary and sufficient to specify centromere identity and function in organisms with point centromeres. In budding yeasts, the centromere region is relatively small (about 125 bp DNA) and contains two highly conserved DNA sequences that serve as binding sites for essential kinetochore proteins.

The formation of a neocentromere must be coupled with or followed or proceeded by the inactivation of the centromere since chromosomes with two functional centromeres (Dicentric chromosome) will result in chromosome breakage during mitosis.In some unusual cases human neocentromeres have been observed to form spontaneously on fragmented chromosomes. Some of these new positions were originally euchromatic and lack alpha satellite DNA altogether.

Source: Wikipedia > Centromere