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Cell Division
Suzanne D'Anna
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Cell Division
process by which cells reproduce
themselves
 Includes:
- nuclear division
- cytoplasmic division
 Two types:
- somatic cell division
- reproductive cell division

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Transcription
process by which genetic information
encoded in DNA is copied onto a strand
of RNA
 when strands divide, one strand (the
sense strand) acts as the template for
mRNA synthesis
 the other strand is called the antisense
strand

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What is DNA?
composed of building blocks called
nucleotides
 double strand of nucleotides
 ladder-like molecule
 coiled into a spiral
 double helix

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DNA Replication
DNA helix uncoils
 gradually separates into two nucleotide
chains
 template for next strand
 each nucleotide joins in a
complementary sequence

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Nucleotide Structure

Composed of:
- nitrogenous base
- pentose monosaccharide
- phosphate groups
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Nucleotide Structure

(cont.)
nitrogenous base
- purines (adenine and guanine)
- pyrimidines (cytosine, thymine, and
uracil
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DNA

DNA bases:
- adenine
- guanine
- cytosine
- thymine
(A)
(G)
(C)
(T)
adenine (A) bonds with thymine(T)
 guanine (G) bonds with cytosine (C)

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RNA

RNA bases:
- adenine (A)
- guanine (G)
- cytosine (C)
- uracil (U)
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Messenger RNA

carries genetic information from DNA to
cytosol where it serves as template for
protein synthesis
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Translation
process by which nucleotide sequence
on a strand of mRNA is used as a
template for protein synthesis
 generates a corresponding amino acid
sequence in a polypeptide chain
 three consecutive nucleotides are called
a codon, which specifies one amino
acid

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Somatic Cell Division

results in an increase in number of cells
in body (growth, repair)

Cell life cycle has two major periods:
- interphase (resting stage)
- mitotic phase (cell division
reproduction occurs)
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Interphase
series of activities before reproduction
 between divisions
 each chromosome makes copy of self
 two identical chromosomes
 chromatids are united by centromere
 metabolic activities continue
 longest phase of the cell cycle
 very active

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Cell Division

Process includes:
- mitosis
nuclear division
formation of two daughter nuclei
- cytokinesis
division of cytoplasm
begins once mitosis is nearly
complete
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Stages of Mitosis
prophase
 metaphase
 anaphase
 telophase

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Prophase
(pro = before)
chromosomes become visible as
chromatids
 nucleolus disappears
 mitotic spindle appears

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Prophase
(cont.)
chromatin threads coil and shorten into
chromosomes
- double stranded (chromatids)
 each chromatid is held together by
small median body called a centromere
 centrosome and its centrioles each
move to opposite sides of cell

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Prophase
(cont.)
mitotic spindle between centrioles
(responsible for attachment and
movement of chromosomes)
 end of stage - nuclear membrane and
nucleoli have broken down and
disappeared
 chromosomes are randomly attached to
centromeres by spindle fibers

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Prophase
Prophase 1
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Prophase 2
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Metaphase
(meta = after)
short
 chromosome pairs line up on the
metaphase plate (exact midpoint or
center of the mitotic spindle)
 straight line of chromosomes

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Metaphase
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Anaphase
(ana=upward)
centromeres divide and separate
 identical chromosomes move to
opposite poles with centromeres

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Anaphase
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Telophase
(telo = far or end)
begins as soon as chromosomal
movement stops
 chromosomes at poles uncoil
 resume chromatin form (threadlike)
 nuclear membrane forms around each
chromatin mass
 nucleoli reappear
 mitotic spindle disappears

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Telophase
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Cytokinesis
(kinesis = motion)
division of cytoplasm and organelles
 occurs in late anaphase
 furrow develops and progresses inward
dividing cell into two separate portions
of cytoplasm

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Conclusion
two daughter cells genetically identical
to the original mother cell
 each cell diploid in number

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Meiosis
cell division
 restricted to sex cell (gametes)
production
 involves two successive nuclear
divisions
 results in daughter cells with haploid
(1/2) number of chromosomes

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Haploid

one half the normal number of
chromosomes (23 in humans)
Diploid

number of chromosomes
characteristically found in somatic cells
of an organism (46 in humans)
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