Interphase and the five stages of mitosis

The chromosomes are shown in blue, and the centrosomes, asters, and spindle fibers are shown in green (1 of 2)The chromosomes are shown in blue, and the centrosomes, asters, and spindle fibers are shown in green (1 of 2)

Centrosomes (with centriole Chromosomes pairs) (duplicated) Nucleolus Plasma 2:65: e membrane p The G2 interphase cell pictured here has passed through GI and 5 phases, during which the chromosomes duplicate. Although duplicated, the chromosomes are diffuse and not visible within the nucleus. An intact nuclear envelope encloses the chromosomes and one or more nucleoli. Two centrosomes, each containing a centriole pair, are located in the cytoplasm. Micro- tubules begin to extend from the centrosomes in radial patterns that form asters. Early mitotic spindle Aster Chromosome, Centromere consisting of two sister chromatids Chromosome condensation begins in and progresses throughout prophase, making the coalescing chromosomes increasingly visible under the light microscope. In the cytoplasm, the paired centrosomes begin to migrate toward opposite poles of the cell, extending their microtubules to form the early mitotic spindle. By the end of prophase, the two sister chromatids that make up each chromosome can be seen. Centromeres can also be seen on late—prophase chromo- somes. The nucleolus disappears. Prometaphase Nonkinetochore microtubule Fragments of nuclear envelope 6 Kinetochore microtubule Astral microtubules Kinetochore Nuclear envelope breakdown occurs during prometaphase. Having reached opposite poles of the cell, the centrosomes extend microtubules that attach to kinetochores of chromosome centromeres. Micro- tubules extending from opposite poles exert pulling forces in both directions. Chromosomes move toward the middle of the cell. Cohesin binds sister chromatids to resist premature separation due to pulling forces. Nonkinetochore and astral microtubules stabilize the cell.