8.1.3 Mitosis: The Phases

Question 1

note

Answer 1

• Review: Mitosis is the process of nuclear division that requires the doubling of a cell’s DNA (in S phase of interphase) so that each resulting cell has a copy of the genetic information.
  • Mitosis is divided into five phases: prophase, prometaphase, metaphase, anaphase, and telophase.

Question 2

phases

Answer 2

• Before mitosis begins (during late interphase), the
  centrosome doubles and microtubules (protein polymers) begin to grow out of them to form the asters.
• During prophase, DNA condenses into chromosomes that are visible with a light microscope. The nucleolus disappears and the spindle begins to form out of the asters as the centrosomes start to migrate from each other to opposite poles.
• In prometaphase the nuclear envelope breaks into
  fragments. The centrosomes have migrated to each pole. Some of the spindle fibers attach to the kinetochores of chromosomes.
• During metaphase the chromosomes are aligned at the metaphase plate (the equator of the cell) by the
  microtubules. The array of microtubules at the metaphase plate is called the spindle because they look like a spindle.
• During anaphase the chromatids of each chromosome
  separate and move to opposite poles. Motor molecules at the kinetochore of each chromatid move along microtubules as they shorten, resulting in the separation of chromatids. As this happens, the cell elongates
• Finally, in telophase the cleavage furrow forms and the cell begins to divide. The nuclear envelope and nucleolus reform and DNA becomes less condensed

Question 3

The nuclear envelope fragments, the centrosomes move apart from one another, and the chromosomes begin to move during which phase?

Answer 3

• Prometaphase

Question 4

Colchicine is a poison that stops spindle fiber formation. If a eukaryotic cell is exposed to colchicine and undergoes mitosis, which stage will the cell not be able to enter?

Answer 4

• prometaphase

Question 5

During which mitotic phase do the spindle fibers disassemble?

Answer 5

• Anaphase

Question 6

In a cell undergoing mitosis, the centromeres uncouple and sister chromatids begin to move to opposite poles during which phase?

Answer 6

• anaphase

Question 7

Spindle fibers are composed of

Answer 7

• proteins

Question 8

If a cell with six chromosomes undergoes cell division, how many chromatids will it have at metaphase of mitosis?

Answer 8

• 12