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Cell Division(Mitosis)
Section 10-2
Chromosomes
In our cells the genetic information that is carried from one generation to the next is carried by chromosomes– Chromosomes are
made up of DNA– Every organism has
a specific number of chromosomes
Fruit Fly =8 (4 pair) Human = 46 (23 pair) Carrot = 18 (9 pair)
Chromosomes– Chromosomes are not
visible in most cells except during cell division
– Before cell division, each chromosome is replicated, or copied
– Because of this, at the beginning of cell division each chromosome consists of two identical sister chromatids
Each pair of chromatids are attached at an area called a centromere
Centromere
Sister Chromatids
Replicated Chromosomes
The Cell Cycle During the cell cycle, a
cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again
The cell cycle consists of two distinct phases– Interphase– M (Mitotic)-phase
The Cell Cycle (Mitosis)
Interphase
Interphase is broken down into three different steps (This is not necessarily part of mitosis)– G1(Gap1)Phase
This is a period in which the cell does most of its growing
– S (Synthesis)PhaseThis is when the chromosomes are replicated
– G2(Gap2) PhaseThe organelles and other molecules required
for cell division are produced
Cell Cycle
When the events of G2 are complete the cell is ready to enter the M (mitotic)-Phase
Mitosis can be divided into four different phases:– Depending on the type
of cell:– the four phases of
mitosis can last a few minutes or several days
1. Prophase
The longest phase of mitosis
The chromosomes become visible
Centrioles, which are two tiny structures located in the cytoplasm near the nuclear envelope, separate and move to opposite sides of the nucleus
Prophase The spindle fibers form
– These are fanlike microtubule structure that helps to separate the chromosomes
Chromosomes become attached to the spindle fibers at the centromere of each chromatid
Nucleolus (ribosomes are made here) disappears as does the nuclear envelope
Prophase
2. Metaphase
Second phase of mitosis
Lasts only a few minutes
The chromosomes line up across the center of the cell
Metaphase
3. Anaphase
Third phase of mitosis The centromeres that
join the sister chromatids separate
Allows the chromatids to separate and become individual chromosomes
These chromosomes continue to move until they have separated into two groups on opposite sides of the cell
Anaphase
4. Telophase
Fourth phase of mitosis
Everything that happened during prophase is reversed
The spindle fibers disappear
Two new nuclear membrane are formed
Chromosomes are wrapped up
Chromosomes turns back into chromatins
Telophase
Cytokinesis
At the end of mitosis, two nuclei--each with a duplicate set of chromosomes--are formed
All that remains to complete the cell cycle is cytokinesis, the division of the cytoplasm
Cytokinesis usually occurs at the same time as telophase
Cytokinesis
Cytokinesis can take place in a number of ways
In animal cells the cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts– Each part contains
its own nucleus and organelles
Cytokinesis in Animal Cells
Cytokinesis
In plants a cell plate forms midway between the divided nuclei
The cell plate gradually develops into a separating membrane
A cell wall then begins to appear in the cell plate
Cytokinesis in Plant Cells
Mitosis in Onion Root Tip