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Chapter 10
Cell Division
Prokaryotic Division
Chromosomes
(colored bodies)
 Prokaryotes have a single, circular
chromosome
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Prokaryotics

Cell Division

Prokaryotes (bacteria)
reproduce through cell
division

Binary fission

Circular chromosome (DNA)
is replicated

Replicated chromosomes are
attached to the cell
membrane at nearby sites
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As membrane expands, the
copies separate
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New cell wall forms between
copies, cell splits
What about eukaryotic division?
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Mitosis
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Eukaryotes use cell division to create new cells
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MITOSIS: division of the nucleus
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Growth, Maintenance and Repair
Asexual cell division
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Reproduction
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MEIOSIS: a special, two-stage type of mitosis that results in
daughter cells with half as many chromosomes as the parent
cells
Humans

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46 chromosomes
Diploid state (2n = 46)
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2 sets of 23 chromosomes
(diploid)

n = number of
chromosomes in a set
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Fundamental number,
haploid number
In humans 23
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n = contribution from each
parent
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#23 = 1 sex chromosome, #122 autosomes
Chromosomes

Maternal
Paternal
Sex:
X or X
X or Y
Autosomes #:
1
1
2
2
ä
ä
22
22
(homologous pairs)
The Cell Cycle
 The
Cell Cycle shows the stages of
life of a cell
Cellular Division

Cell division is how a cell makes a copy itself

A cell spends most of its life in interphase
 1st stage = G1, a growth phase; the number of organelles
and the amount of cytoplasm double
 2nd stage = S phase; DNA replicates (the chromatins turn
into chromosomes)
 chromatins – loose uncoiled strands of DNA
 chromosomes – DNA wrapped around proteins
 How does DNA replicate? DNA Replication
 3rd stage = G2, another growth phase; the cell will
continue to grow
The Cell Cycle
Cellular Division

After interphase, the cell goes through mitosis


Mitosis is the next 4 phases of cellular division
Mitosis occurs in all eukaryotic cells


Only in your somatic cells
Eukaryotic cells are cells that have a nuclei
and membrane bound organelle
 Somatic cells are all body cells except for egg
cells and sperm cells
Mitosis Overview
Phases of Mitosis
First Phase – Prophase
 What happens during prophase?

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1. Chromosomes condensed - become thicker
2. The nucleolus and nuclear membrane break
down and disappear
3. Centrioles move to opposite sides of the cell
4. Spindle Fibers appear and radiate from the
centrioles

Spindle fibers are protein tubes
What does prophase look like?
Phases of Mitosis
Second Phase – Metaphase
 What happens during metaphase?

1. Chromosomes move to the middle of the
cell
 2. Spindle fibers are attached to the
chromosomes controlling their movement

What does metaphase look like?
Phases of Mitosis
Third Phase – Anaphase
 What happens during anaphase?
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1. The centromere breaks down
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The centomere holds the chromosomes together
2. The spindle fibers pull apart the
chromosome

Separating the sister chromatids
What does metaphase look like?
Phases of Mitosis
Fourth Phase – Telophase
 What happens in telophase?
 1. Nuclear membrane forms around
chromatids


This Forms a nucleus with a nucleolus
2. Chromatids turn into chromatins
 3. The cell membrane starts to pinch
inward to separate into 2 new cells
 4. Centrioles and spindle fibers disappear

What does telophase look like?
Phases of Mitosis

Cytokinesis is the last stage of cell
division
During cytokinesis the 2 cells actual split
apart from each other
 In a plant cells, a cell plate grows between
to the two new cell
 The cell plate develops into the cell wall

What does cytokinesis look like?