Cell Division (Mitosis)

1
Cell Division(Mitosis)

• Section 10-2

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)

3
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

4
Replicated Chromosomes

• Centromere
• Sister Chromatids

5
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

6
The Cell Cycle (Mitosis)
7
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)Phase
• This is when the chromosomes are replicated
• G2(Gap2) Phase
• The organelles and other molecules required for
  cell division are produced

8
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

9
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

10
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

11
Prophase
12
2. Metaphase

• Second phase of mitosis
• Lasts only a few minutes
• The chromosomes line up across the center of the
  cell

13
Metaphase
14
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

15
Anaphase
16
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

17
Telophase
18
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

19
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

20
Cytokinesis in Animal Cells
21
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

22
Cytokinesis in Plant Cells
23
Mitosis in Onion Root Tip