LIFE 120 Lecture Notes - Lecture 9: Microtubule Organizing Center, Spindle Apparatus, Sister Chromatids
Document Summary
The mitotic spindle is a structure made of microtubules and associated proteins. The diploid nucleus has two pairs of homologous chromosomes. One haploid set is black, the other is gray. In animal cells, assembly of spindle microtubules begins in the centrosome, the microtubule organizing center. The centrosome replicates during interphase, forming two centrosomes that migrate to opposite ends of the cell during prophase and prometaphase. An aster (radial array of short microtubules) extends from each centrosome. The spindle includes the centrosomes, the spindle microtubules, and the asters. During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes. Kinetochores are protein complexes that assemble on sections of dna at centromeres. At metaphase, the centromeres of all the chromosomes are at the metaphase plate, an imaginary structure at the midway point between the spindle"s two poles. In anaphase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell.
