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Cell Division
Cell Division:
• The process by which a cell divides into two
new daughter cells is called cell division.
• Before cell division occurs, the cell replicates
or copies its entire DNA. This replication of
DNA solves the problem of information
overload because each daughter cell gets one
complete copy of genetic information.
Name we use to describe the new
cells that are created.
Two types of reproduction:
• Asexual Reproduction
– The production of genetically identical offspring
from a single parent.
– Enables populations to replicate very quickly.
– Bacteria and many single-celled organisms.
Two types of reproduction:
• Sexual Reproduction
– Offspring produced by sexual reproduction inherit
some of their genetic information from each
parent.
– Involves the fusion of two separate parent cells.
– Most plants and animals.
The process of cell division:
• What do you think would happen if a cell were
simply to split in two, without any advance
preparation?
The process of cell division:
• Even small cells like the bacterium E. coli have
tremendous amounts of genetic information in the
form of DNA.
– The total length of this bacterium’s DNA molecule is
roughly 1000x longer that the cell itself.
– Genetic information is bundled into packages of DNA
known as chromosomes.
Prokaryotic Chromosomes
• Prokaryotes lack a nuclei and many of the
organelles found in eukaryotes. Their DNA
molecules are found in the cytoplasm along with
most of the other contents of the cell.
• What do prokaryotic chromosomes look like?
Eukaryotic Chromosomes
• Eukaryotic cells generally have
much more DNA than prokaryotes
and, therefore, contain multiple
chromosomes.
– Fruit flies have 8 chromosomes per
cell
– Human cells have 46 chromosomes
per cell
– A carrot has 18 chromosomes per
cell.
Eukaryotic Chromosomes
• Chromatin = chromosomes which are tightly
coiled around histones (proteins).
Eukaryotic Chromosomes
• Chromosomes make it possible to separate DNA
precisely during cell division.
The Cell Cycle:
• Cells go through a series of events known as the
cell cycle as they grow and divide.
• During the cell cycle a cell:
– Grows
– Prepares for division
– Divides to form two daughter cells.
Prokaryotic Cell Cycle:
• The prokaryotic cell cycle is
a regular pattern of
growth, DNA replication,
and cell division that can
take place very rapidly
under ideal conditions.
• Form of asexual
reproduction known as
binary fission.
Eukaryotic Cell Cycle:
• Consists of four phases: G1, S, G2, and M.
• The length of each phase and the length of the
entire cell cycle vary depending on the type of cell.
G1 Phase: Cell Growth
• Cells do most of their growth
• Cells increase in size and synthesize new proteins
and organelles.
• “G” stands for “gap”
– However; both G1 and G2 are actually periods of intense
growth and activity.
S Phase: DNA Replication
• “S” stands for “synthesis”
• New DNA is synthesized when the chromosomes
are replicated.
• At the end of the S phase the cell contains twice as
much DNA as it did at the beginning.
G2 Phase: Preparing for division
• Many of the organelles and molecules required for
cell division are produced.
• When the events of this phase are completed the
cell is ready to enter the M phase.
M-Phase: Preparing for division
• Produces two daughter cells.
• “M” stands for “mitosis”
**Both “G”
phases and “S”
phase are part of
Interphase.
Two types of Cell Division
1) Mitosis:
– Biologists divide the events of mitosis into four
phases: prophase, metaphase, anaphase, and
telophase. Depending on the type of cell, mitosis may
last anywhere from a few minutes to several days.
• Centromere – the area where the duplicated DNA
strands are held together.
• Chromatid – each DNA strand in the duplicated
chromosome.
• Centrioles – organelles which will aid in the
division of the cell.
Cytokinesis:
• Completes the process of cell
division – splits one cell into two.
• In Animals:
– The cell membrane is drawn inward
until the cytoplasm is pinched into
two nearly equal parts.
• In Plants:
– A cell plate forms halfway between
the divided nuclei, and gradually
develops into two cell membranes.
The cell wall then forms between the
two new membranes.