2. Overview of Cell Division
Phases of Cell Division
Molecular mechanisms in Cell Division
Important structures and key components in DNA
synthesis
DNA polymerases and the process of DNA replication
Proof reading and repair
Regulation of Cell Cycle
3.
4. Most eukaryotic cells will
pass through an ordered
series of events in which the
cell duplicates its contents
and then divides into two
cells
This process of cell division
in multicellular organisms
must be highly ordered and
tightly regulated
5.
6. Mitosis is the process by which a eukaryotic cell
duplicates its DNA and then divides into two
daughter cells, each of which contains the exact
genetic material as the mother cell and gets
roughly an equal share of other cellular
components
If the DNA of a human cell were uncoiled and
stretched, it would extend approximately 2
meters!
7. Meio: to reduce
A form of nuclear division in which the
chromosome number is halved from the diploid
number (2n) to haploid number (n)
It is preceded by DNA replication during
interphase in the parent cell. This is followed by
2 cycles of nuclear division and cell divisions-
Meiosis I and Meiosis II
8. Mitosis generates two
genetically identical diploid
daughter cells
Meiosis generates four haploid
daughter cells, none of which are
genetically identical
9. Starting from a single-celled zygote… An adult
human being has approximately 100,000 billion
cells
Cell division does not stop with formation of
mature organism, but continues throughout its
life
Tens of millions of cells undergo division at any
given moment in an adult human. This amount of
division is needed to replace cells that have aged
or died
10. Two major cell cycle phases - based on cell
activities readily visible under light microscope:
Interphase - occupies bulk of cycle; divided into G1
(first gap), S (synthesis) & G2 (second gap)
M phase – M for "mitotic"; this stage includes mitosis
(duplicated chromosomes are separated into 2 nuclei)
& cytokinesis (entire cell & its cytoplasm divide into 2
daughter cells)
11. G1 - growth phase 1
S - DNA synthesis
G2 - further growth
M - cell division
Mitosis:
– prophase, prometaphase,
metaphase, anaphase
and telophase
Cytokinesis
InterphaseMitoticphase
12.
13. G1 (G=gap) is the interval between the
completion of mitosis and the beginning of DNA
synthesis
During G1, the cell monitors its own
environment and size before it commits itself to
DNA replication. Cells in G1 (if not committed to
DNA replication) can pause their progress and
enter a specialized resting state G0
S phase - replication of nuclear DNA
Interphase Mitotic phase
G1 S G2 Pro Prometa Meta Ana Telo
14. G2 is the second “Gap” phase:
Nucleus well defined and bound by nuclear
envelope
Outside nucleus are two pairs of centrioles
formed during early interphase
Microtubules extend from centrioles in a radial
array called asters
Interphase Mitotic phase
G1 S G2 Pro Prometa Meta Ana Telo
15. Interphase Mitotic phase
G1 S G2 Pro Prometa Meta Ana Telo
Prophase
Changes occurs in both nucleus and cytoplasm
Nucleus: Chromatin fibres become more tightly
coiled and condense into discrete chromosomes.
The duplicated chromosome appears as 2
identical sister chromatids joined by centromere
Cytoplasm: formation of mitotic spindle begins
16. Interphase Mitotic phase
G1 S G2 Pro Prometa Meta Ana Telo
Prometaphase
Nuclear envelope develop fragments.
Microtubules can now invade the nucleus and
interact with the chromosomes
Microtubule attach to kinetochore on each
chromosomes centromere
Asters, radiate from centrioles and anchor
themselves to membrane plasma
18. Interphase Mitotic phase
G1 S G2 Pro Prometa Meta Ana Telo
Metaphase
Centrioles at opposite poles of the cell
Chromosome convene on the metaphase plate
(imaginary plane of equal distant between
spindles of two poles)
20. Interphase Mitotic phase
G1 S G2 Pro Prometa Meta Ana Telo
Anaphase
Begins when paired centromeres of each
chromosome separate, liberating each sister
chromosome from one another (each chromatid
is considered one full fledged chromosome)
Chromosomes begin moving along microtubule
toward opposite poles of the cell
21. Interphase Mitotic phase
G1 S G2 Pro Prometa Meta Ana Telo
Telophase
Nucleolus begins to form at the two poles of the
cells. Nuclear envelopes are formed
Chromatin fibre of each chromosome become
less tightly coiled
Mitosis ends and cytokinesis begins
22. Interphase Mitotic phase
G1 S G2 Pro Prometa Meta Ana Telo
Cytokinesis
Occurs by a process called cleavage: begins with
a cleavage furrow, a shallow grove near the
metaphase plate
In cytoplasmic side of the furrow, are contractile
actin proteins. As the actin microfilament
contract, its diameter shrinks, cleavage furrow
deepens until cell pinched into two
26. DNA replication begins at specific locations in
the genome, called "origins“
Unwinding of DNA at the origin, and synthesis of
new strands, forms a replication fork. In addition
to DNA polymerase, the enzyme that synthesizes
the new DNA by adding nucleotides matched to
the template strand, a number of other proteins
are associated with the fork and assist in the
initiation and continuation of DNA synthesis
27. The replication fork is a structure that forms
within the nucleus during DNA replication. It is
created by helicases, which break the hydrogen
bonds holding the two DNA strands together
The resulting structure has two branching
"prongs", each one made up of a single strand of
DNA
28. DNA polymerases are a family of enzymes that
carry out all forms of DNA replication
To begin synthesis, a short fragment of DNA or
RNA, called a primer, must be created and paired
with the template DNA strand
DNA polymerase then synthesizes a new strand
of DNA by extending the 3' end of an existing
nucleotide chain, adding new nucleotides
matched to the template strand one at a time via
the creation of phosphodiester bonds
29.
30. The PCR does in the test tube what every
bacterium does in its tube of media or on an
agar-plate and each of us do every day: we all
produce billions of exact copies of our own DNA;
AMPLIFYING our DNA millions of time
The enzyme DNA polymerase was discovered in
the 1950s and our knowledge of the process has
been increasing ever since
31. TARGET DNA to be copied. In theory only a single
molecule is needed
A set of short (15 to 40 bases) single stranded PRIMERS
of DNA, that will bind to complementary regions of the
opposing stands of the target DNA molecule
An excess of the 4 nucleotide triphosphates, ATP, GTP,
CTP, TTP
The enzyme, DNA polymerase
Various buffers and cofactors like magnesium ions
required by DNA polymerase
32. Double helix target DNA strands are separated so
the primers could bind and the DNA polymerase
could function
Heat separates DNA strands and that
complementary strands then rejoin through base
pairing when the temperature is subsequently
lowered
33. Lowering the temperature enough to allow the
primers, which were small and in vast excess, to
bind (ANNEAL) to their respective
complementary target DNA sequence
DNA polymerase allows polymerization reaction
with the triphosphate nucleotides to occur
36. The DNA polymerase fills in the missing portion
of each strand making two new double stranded
regions of DNA
The whole process is repeated several times thus
yielding exponential amount of DNA strands
2 4 8 16 32 After 12 cycles… 8192
After 20 cycles… 2097152
37. Beginning with a single piece of DNA, PCR can generate
100 billion identical copies of a specific DNA sequence !!!
38. PCR takes place in a tube which is kept in a
machine called “thermal cycler”
39.
40. For all living eukaryotic organisms it is essential
that the different phases of the cell cycle are
precisely coordinated
Errors in this coordination may lead to
chromosomal alterations. Chromosomes or parts
of chromosomes may be lost, rearranged or
distributed unequally between the two daughter
cells
42. Much of the control of the progression through the
phases of a cell cycle are exerted at checkpoints
There are many such checkpoints but the three
most critical are those that occur near the end of
G1 prior to S-phase entry, near the end of G2 prior
to mitosis, and at metaphase…