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My name is Poon Cheng Moh. I have been teaching biology in SMK(P) Raja Zarina, Port Klang for 26 years. I sincerely hope that this blog on SPM Biology will be useful to both teachers and students.

Friday, May 8, 2015

How a cell cycle works



• The chromosomes in the nucleus condense and become more tightly coiled.
• Each chromosome now consists of a pair of sister chromatids joined together at the centromere.
• In the cytoplasm, the spindle fibres begin to form and extend between the centrioles.
• Each pair of centrioles then migrates to lie at the opposite poles of the cell. The chromatids are attached to the fibres of the spindle by their centromeres.
• At the end of prophase, the nucleolus disappears and the nuclear membrane disintegrates.

• Metaphase begins when the centromeres of all the chromosomes are lined up on the metaphase plate, an imaginary plane across the middle of the cell.
• The mitotic spindle is now fully formed.
• The two sister chromatids are still attached to one another at the centromere.
• Metaphase ends when the centromere divide.

• During anaphase, the two sister chromatids of each chromosome separate at the centromere.
• The sister chromatids are pulled apart to the opposite poles by the shortening of the spindle fibres.
• Once separated, the chromatids are referred to as daughter chromosomes.
• By the end of anaphase, the two poles of the cell have complete and equivalent sets of chromosomes.

• Begins when the two sets of chromosomes reach the opposite poles of the cell.
• The chromosomes start to uncoil and revert to their extended state (chromatin).
• The chromosomes become less visible under the microscope.
• The spindle fibres disappear and a new nuclear membrane forms around each set of chromosomes.
• The nucleolus also reforms in each nucleus.
• The process of mitosis is now completed.