THE MITOTIC CELL CYCLE
PREPARED BY
Dr. S.SELVAKUMARI
5.1 Replication and division of nuclei and cells
a. Describe the structure of a chromosome, limited to DNA, histone proteins,
chromatids, centromere and telomeres.
b. Explain the importance of mitosis in the production of genetically identical cells,
growth, cell replacement, repair of tissues and asexual reproduction.
c. Outline the cell cycle, including interphase (growth in G1 and G2 phases and DNA
replication in S phase), mitosis and cytokinesis.
d. Outline the significance of telomeres in permitting continued replication and
preventing the loss of genes.
e. Outline the significance of stem cells in cell replacement and tissue repair by
mitosis and state that uncontrolled cell division can result in the formation of a
tumor.
4.2 Chromosome behavior in mitosis
a. Describe, with the aid of photomicrographs and diagrams, the behavior of
chromosomes in plant and animal cells during the mitotic cell cycle and the
associated behavior of the nuclear envelope, cell surface membrane and the
spindle (names of the main stages of mitosis are expected).
b. Observe and draw the mitotic stages visible in temporary root tip squash
preparations and in prepared slides of root tips of species such as those of Vicia
faba and Allium cepa.
Chromosome and DNA
• Chromosomes controls cell activities
• Are copied from cell to cell when cells divide
Chromatin – at normal time
Chromosome – at cell division time
Chromosome and DNA
• Position of centromere is fixed for any
chromosome and the length of a chromosome
is also characteristic
• The number of chromosomes per species is
fixed
• Chromosomes occurs in pairs
• Chromosomes are copied between nuclear
divisions.
1.8 meters of DNA
has to be packed
into a nucleus of 6
µm diameter.
A combination of
DNA and proteins is
called chromatin.
DNA Double Helix
Phosphodiester
bond
Pentose sugar
Ribose
Deoxyribose
Major Groove
Phosphate
group
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•
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•
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DNA: DeoxyriboNucleic Acid
RNA: RiboNucleic Acid
Bases:
Adenine (A) and Guanine (G) = Purines
Cytosine (C) & Thymine (T) = Pyrimidines
RNA has Uracil instead of Thymine
Base sugar = Nucleoside (Deoxyribonucleoside & Ribonucleoside)
Base sugar and phosphate unit = nucleotide . Many form a polynucleotide
Phosphodiester bonds = link nucleotides for nucleic acid polymer
Hydrogen bonding between paired bases
Each chain is complimentary
DNA Packaging
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Chromatin –
DNA bound to
histones (DNA
packaging
proteins)
DNA and
histones are
organised into
nucleosomes.
Eight histones
= histone
octamer
These are
linked by
linker DNA
Minor Groove
RNA
• DNA transcribed into mRNA by RNA polymerase
• RNA used as a primer in DNA replication
• Ribosomal RNA
• tRNA aids in translation of mRNA into protein
DNA replication
1. Double helix is unwound and the base-pairs are separated
by DNA helicase.
2. Semi-conservative replication
3. Nucleotides are linked covalently by DNA polymerase
4. Lagging and leading strands
5. DNA ligase for the shorts strands on the lagging strand
PACKAGING OF DNA IN CHROMOSOME
147 bps
Linker DNA- 53 bps
TELOMERE
Kinetochore and centromere
Cell Division Mitosis
Significance of Mitosis
There are three main reasons
A. growth
B. repair/healing
C. asexual reproduction
https://www.youtube.com/watch?v=DwAFZb8juMQ
Cell Division – Two types
• Mitosis– Division of somatic cells
• Meiosis –Creation of new sex cells
Vocabulary
Somatic cell – a body cell; a cell whose genes will not be passed on
to future
Homologous Chromosomes– A pair of chromosomes that code for
the same types of proteins.
Telomere – end of chromosome which serves to protect it by
permitting continued replication and preventing the loss of genes
Germ cell - a cell that is destined to become a gamete (egg or
sperm); a cell whose genes can be passed on to future generations
Diploid (2N) – a cell with 2 chromosome sets in each of its cells; all
body (somatic) cells
Haploid (N) – a cell with 1 chromosome set in each of its cells; all
gametes (sperm, eggs)
Features of Mitosis
Cell Cycle
• Chromosome number remains the
same
• The DNA remains identical.
• One cell gives rise to 2 cells
Cell Cycle
• The longest phase in the cycle is
interphase
• The 3 stages of interphase are
called G1, S and G2.
G1- cells make RNA, enzymes and
other proteins needed for growth
S- synthesis of DNA takes place
G2- the cell continues to grow and
new DNA is checked and any errors are
usually repaired.
Cell Cycle
Overview of Mitosis
Prophase
• In Prophase, the cells begin the process of cell division
1. The chromosomes condense.
2. Nuclear envelope disappears.
Nucleolus gradually disappears.
3. In animals, the centrosome divides
and the two centrioles replicate to
form two centrosomes.
Prophase
• In Prophase, the centrioles
migrate to the opposite
poles of the cell.
• Asters and spindle fibres
form
Draw Prophase
Metaphase
• In Metaphase, the chromosomes line up at the equator of the cell
(metaphase plate), with the centrioles at opposite ends and the spindle
fibres attached to the centromeres
Images of Metaphase stage of Mitosis
Anaphase
• In Anaphase, the centromeres
divide
• At this point, the sister
chromatids separate and form
individual chromosomes.
Draw Anaphase