CELL DIVISION AND CELL CYCLE
Cell division is the process by which a parent cell divides into 2 daughter cells. In UNICELLULAR
ORGANISMS, cell division produces new organisms, meaning it is also a way of
REPRODUCTION.
In MULTICELLULAR ORGANISMS it aids in reproduction, but also in tissue growth, maintenance
and repair.
CELL DIVISION IN PROKARYOTES: BINARY FISSION
Binary fission is a kind of asexual reproduction (the daughter cells are identical to the parent
cell), and the most common form of reproduction in prokaryotes. In binary fission the fully
grown parent cell splits into 2 halves, producing 2 daughter cells.
STEPS TO BINARY FISSION
1. The cell elongates by building more cell wall
2. All genetic material duplicates
3. Each DNA copy moves towards the cell’s poles
4. The cleavage furrow begins to form
5. Cell wall forms in the cleavage furrow
6. 2 identical daughter cells are produced
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CELL DIVISION IN EUKARYOTES: THE CELL CYCLE
The cell cycle is an ordered series of events involving cell growth and cell division. The cell
cycle has two major phases: INTERPHASE and the MITOTIC PHASE. During interphase, the cell
grows, and DNA is replicated. During the mitotic phase, the replicated DNA and cytoplasmic
contents are separated, and the cell divides.
INTERPHASE
During interphase, the cell undergoes normal growth processes while also preparing for cell
division. The three stages of interphase are called G1, S, and G2.
G1 PHASE (FIRST GAP)
The cell is working on different cellular processes. The cell is accumulating sufficient energy
reserves to complete the task of duplicating DNA in the nucleus.
S PHASE (SYNTHESIS OF DNA)
DNA duplicates, forming 2 identical pairs of DNA.
G2 PHASE (SECOND GAP)
The cell replenishes its energy reserves and makes the proteins and organelles necessary for
the mitotic phase.
MITOTIC PHASE (M PHASE)
Is a process in which the duplicated DNA are separated and move into the new identical
daughter cells. The first portion is called MITOSIS or nuclear division, the second portion is
called CYTOKINESIS, and is the physical separation of the cytoplasm.
MITOSIS is a multi-phase process in which the nucleus of the cell divides
1. PROPHASE: The DNA stores into chromosomes that then attach to the centrioles
through the spindle fibers.
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2. METAPHASE: the chromosomes are pulled by the spindle fibers and arrange
themselves in the cell’s equator.
3. ANAPHASE: Each pair of chromosomes separates and start to move towards the cell’s
poles thanks to the spindle fibers.
4. TELOPHASE: the spindle fibers disappear after the DNA reaches the cell’s poles. A
nuclear membrane starts to form around each set of DNA.
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CYTOKINESIS is the phase during which cell division is completed thanks to the physical
separation of the cytoplasm. Although the stages of mitosis are similar for most
eukaryotes, the process of cytokinesis can be different according to each cell.
In animal cells, cytokinesis happens along with telophase. In these cells, the cell
membrane pinches together, and a furrow begins to form along the equator. The furrow
deepens until the cell membrane separates forming 2 daughter cells.
In plant cells, a new cell wall must form between the daughter cells. For this, a cell plate
is formed in the middle. The cell plate then extends outwards until it separates the 2
daughter cells. Each of the new cells then forms a cell wall on its side of the cell plate.
CELL DIVISION IN EUKARYOTES: MEIOSIS
Meiosis is the process by which eukaryotic organisms reproduce sexually (the daughter cells
are different from the parent cell). Meiosis produces unique reproductive cells called
GAMETES, which have half the number of chromosomes and different DNA information as the
parent cell.
Mitosis creates cells that help in the growth, maintenance and repair of tissues, and can be
found in every part of the body. By contrast, meiosis produces cells that are found only in the
reproductive structures of the organism and are used only for reproduction.
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