Prometaphase
Microtubules finally reach the chromosomes in this phase, because the nuclear envelope surrounding the chromosomes is broken down into vesicles. The microtubules pull on each chromosomes from each direction and the sister chromatids are drawn apart to opposite poles, as other microtubules push the spindle poles apart. The pulls and pushes of the microtubules begin to balance out when metaphase is reached.
Metaphase
Metaphase is the point in the cell cycle when every duplicated chromosome is in line on the spindle equator. Chromosomes in metaphase are condensed because numerous histones are joined tightly to each chromosome. Histones are the proteins around which DNA stretches wrap. When DNA wraps around four histones, a nucleosome is formed. These histones interact with other DNA causing the nucleosomes to coil around each other to form a cylindrical fiber known as a solenoid. Nucleosomes become more and more organized as solenoids are created. This process of organization condenses the chromosomes.
