mitosis in detail

1. MITOSIS
PREPARED BY FATIMA SUNDUS

2. Life Cycle of the Cell
The life cycle of a cell is the period from cell reproduction to the next cell reproduction

3. MITOSIS
MITOSIS that cause division of the cell into two new daughter cells
INTERPHASE
the stage in the life cycle of a cell where the cell grows and DNA is
replicated
95 percent of the life cycle of even rapidly reproducing cells is
represented by the interval between mitosis, called interphase

4. Cell Reproduction Begins with Replication of DNA
 reproduction begins in the nucleus itself.
 The first step is replication (duplication) of all DNA in the chromosomes.
 Only after this has occurred can mitosis take place.
 The DNA begins to be duplicated some 5 to 10 hours before mitosis, and this is completed in 4 to 8
hours.
 The net result is two exact replicas of all DNA.

6. DNA “Proofreading”
 between DNA replication and the beginning of mitosis, there is a period of active repair and
“proofreading” of the DNA strands.
 Wherever inappropriate DNA nucleotides have been matched up with the nucleotides of the
original template strand, special enzymes cut out the defective areas and replace these with
appropriate complementary nucleotides.
 This is achieved by the same DNA polymerases and DNA ligases that are used in
replication.
 This repair process is referred to as DNA proofreading.

9. Because of repair and proofreading, the transcription process rarely makes a mistake. But when a
mistake is made, this is called a mutation
OR
Any change in the DNA sequence of a cell.
OR
Mutations may be caused by mistakes during cell division

10. CHROMOSOMES AND THEIR REPLICATION
 The DNA helixes of the nucleus are packaged in chromosomes.
 The human cell contains 46 chromosomes arranged in 23 pairs.
 there is a large amount of protein in the chromosome, composed mainly of many small molecules of
electropositively charged histones.
 The histones are organized into vast numbers of small, bobbin-like cores.
 Small segments of each DNA helix are coiled sequentially around one core after another.

13. Cell Mitosis
 The actual process by which the cell splits into two new cells is called mitosis.
 mitosis follows automatically within 1 or 2 hours.

14. Mitotic Apparatus: Function of the Centrioles.
 One of the first events of mitosis takes place in the cytoplasm, occurring during the latter part of
interphase in or around the small structures called centrioles.
 two pairs of centrioles lie close to each other near one pole of the nucleus.
 These centrioles, like the DNA and chromosomes, are also replicated during interphase, usually
shortly before replication of the DNA.
 Each centriole is a small cylindrical body about 0.4 micrometer long and about 0.15 micrometer in
diameter, consisting mainly of nine parallel tubular structures arranged in the form of a cylinder.
 the entire set of microtubules plus the two pairs of centrioles is called the mitotic apparatus.

20. Prometaphase.
 nuclear envelope disappear
 multiple microtubules from the aster
attach to the chromatids at the
centromeres,
 where the paired chromatids are still
bound to each other; the tubules
then pull one chromatid of each pair
toward one cellular pole and its
partner toward the opposite pole.