Mitosis, Meiosis, and the Prokaryotes. Eukaryotic cells Mitosis copies DNA and divides a nucleus, producing two identical nuclei Meiosis nuclear division that produces haploid gametes for sexual reproduction. Comparison of Cell Division Mechanisms. Key Points About Chromosome Structure.
B When a chromosome is at its most condensed, the DNA is packed into tightly coiled coils.
multiple levels of coiling of DNA and proteins
C When the coiled coils unwind, a molecule of chromosomal DNA and its associated proteins are organized as a cylindrical fiber.
A Duplicated human chromosome in its most condensed form. If this chromosome were actually the size shown in the micrograph, its two DNA strands would stretch out about 800 meters (0.5 miles).
D A loosened fiber
shows a “beads-on-a-string” organization.
The “string” is the DNA molecule; each “bead”
is one nucleosome.
beads on a string
DNA double helix
core of histones
E A nucleosome consists of part of a DNA molecule looped twice around a core of histone proteins.
Fig. 9-3 (b-e), p. 143
Interval of cell growth before
DNA replication (chromosomes unduplicated)
Interval of cell growth when the DNA is replicated (all chromosomes duplicated)
Interval after DNA replication; the cell prepares to divide
cytoplasmic division; each descendant cell enters interphase
Interphase ends for parent cell
Fig. 9-4, p. 144
A Early Prophase
Mitosis begins. In the nucleus, the chromatin begins to
appear grainy as it organizes and condenses. The
centrosome is duplicated.
Fig. 9-6 (2a), p. 147
The chromosomes become visible as discrete structures as they condense further. Microtubules assemble and move one of the two centrosomes to the opposite side of the nucleus, and the nuclear envelope breaks up.
Fig. 9-6 (2b), p. 147
C Transition to Metaphase
The nuclear envelope is gone, and the chromosomes are at their most condensed. Microtubules of the bipolar spindle assemble and attach sister chromatids to opposite spindle poles.
Fig. 9-6 (2c), p. 147
All of the chromosomes are aligned midway between the spindle poles. Microtubules attach each chromatid to one of the spindle poles, and its sister to the opposite pole.
Fig. 9-6 (2d), p. 147
Motor proteins moving along spindle microtubules drag the chromatids toward the spindle poles, and the sister chromatids separate. Each sister chromatid is now a separate chromosome.
Fig. 9-6 (2e), p. 147
The chromosomes reach the spindle poles and decondense. A nuclear envelope begins to form around each cluster; new plasma membrane may assemble between them. Mitosis is over.
Fig. 9-6 (2f), p. 147
1 Mitosis is completed, and the bipolar spindle is starting to disassemble.
Fig. 9-7a (1), p. 148
3 This contractile ring pulls the cell surface inward as it continues to contract.
Fig. 9-7a (3), p. 148
4 The contractile ring contracts until the cytoplasm is partitioned and the cell pinches in two.
Fig. 9-7a (4), p. 148
A Cancer cells break away from their home tissue.
B The metastasizing cells become attached to the wall
of a blood vessel or lymph vessel. They release digestive enzymes onto it. Then they cross the wall at the resulting breach.
C Cancer cells creep or tumble along inside blood vessels, then leave the bloodstream the same way they got in. They start new tumors in new tissues.
Fig. 9-11, p. 151