DO LIKE! CLIP, SHARE with your friends, and DOWNLOAD for future use. Helloo!!! everyone, I'm student of M.Sc. Microbiology at Parul University, and i've made this presentation on "The Cell Cycle" focusing more on 'Mitosis and Meiosis'. In this document on "The Cell Cycle (Mitosis & Meiosis) I've tried to cover the important points related to Masters, moreover I've used reference books for the content of the presentation. Writer is solely not at all responsible for any kind of faulty information, however it is important to note that utmost care is taken while making this presentation to make the content as more through the point and true as possible. Any issue related to content or anything else must be brought to the contact of creator. Images, Text, Videos, GIFs, etc. used in this presentation are subjected to copyright, and rights are reserved to the original owner of them. Anything used in this presentation which you think you own it, please let the Creator of this presentation know. Thank You!

1. The_Cell_Cycle_Shiven_Trambadia
The Cell Cycle
By, Shiven R. Trambadia
M.Sc. Microbiology Semester-1
Parul University, Ahmedabad.
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2. The_Cell_Cycle_Shiven_Trambadia
The Cell Cycle
● The cell cycle is an ordered series of events. It is the sequence of events by
which a cell duplicates its genome and eventually divides into two daughter
cells.
● The cell cycle has two main phases - interphase and M-phase.
● The period of actual division, corresponding to the visible mitosis, is called M
phase (mitosis phase).
● The Interphase is the time during which the cell is preparing for division by
undergoing both cell growth and DNA replication in an orderly manner.
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3. The_Cell_Cycle_Shiven_Trambadia
● The interphase is further subdivided into;
○ G1 phase (Gap 1, the period between the end of M phase and the start of DNA replication);
○ S phase (Synthesis, the period during which DNA synthesis occurs); and
○ G2 phase (Gap 2, the gap period following DNA replication and preceding the initiation of the
M phase)
● Cells that do not divide enter into G0 state. Most cells in our body are in G0
state.
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4. The_Cell_Cycle_Shiven_Trambadia
Mitosis
● Mitosis was firstly introduced by Walther Flemming in 1882.
● Mitosis partitions newly replicated chromosomes equally into two daughter
cells.
● Mitosis leads to one round of DNA replication followed by one round of
Chromosome segregation and giving rise to two genetically identical daughter
cells.
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5. The_Cell_Cycle_Shiven_Trambadia
Stages of M-phase
● The M-phase starts with karyokinesis (nuclear division), forming two
daughter nuclei and generally ends up with cytokinesis (cytoplasm division).
● Conventionally mitosis is divided into 4 substages: prophase, metaphase,
anaphase and telophase.
● Cells show different physical characteristics when reaching in each of these
phases.
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6. The_Cell_Cycle_Shiven_Trambadia
Microscopic image of Mitosis
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7. The_Cell_Cycle_Shiven_Trambadia
Prophase
● The diffuse chromatin in interphase, now slowly starts to condense during
the beginning of prophase.
● Chromosomes are duplicated during the previous S-phase and consists of
two sister chromatids, which are held together at a constricted region
called, Centromere.
● At centromere, sister chromatids are held together by a membrane of the
SMC (Structural Maintenance of Chromosomes), included in the family of
proteins, called cohesin.
● At the end of prophase, cytoplasmic microtubules disassemble and starts the
formation of mitotic spindle.
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8. The_Cell_Cycle_Shiven_Trambadia
Prophase
● At the end of prophase nucleolus disappears along with the nuclear envelope.
● Most of the cells mark the end of the prophase when nuclear envelope
disrupts. But, nuclear envelope disruption is not universally observed feature
of mitosis. Eg; Yeast cells don’t loose nuclear envelope during cell division.
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9. The_Cell_Cycle_Shiven_Trambadia
Metaphase
● Metaphase is an very dynamic part of the cell cycle.
● Spindle fibres rapidly assemble and disassemble as
they grow out of the Microtubule Organizing
Center (MTOC), seeking out attachment sites at
chromosome.
● For attachment of spindle fibres, each chromosome
has a special structure called kinetochore.
● There are two kinetochores located at the
centromere, on each chromosome facing in opposite
directions.
● Chromosomes are now lined up to the Equator of
the cell.
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10. The_Cell_Cycle_Shiven_Trambadia
Anaphase
● The kinetochore microtubules pull the
two kinetochores towards the opposite
poles, at anaphase.
● The cohesins holding together the two
sister chromatids, are now digested by
another protein, Separase.
● Until anaphase the separase is kept in
active form by another protein, Securin.
● After separation, each chromatid, which
are now called as chromosome, are
pulled towards the polls they face,
opposite to each other. 10

11. The_Cell_Cycle_Shiven_Trambadia
Telophase
● Separated daughter chromosomes
arrive at the poles and the
kinetochore microtubules
disappears, at Telophase.
● Still polar microtubule elongates
more, and a new nuclear
envelope re-forms around each
set of daughter chromosomes.
● Condensed chromatin expands
again and the nucleoli reappears,
marking the end of the mitosis.
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12. The_Cell_Cycle_Shiven_Trambadia
Cytokinesis
● Division of cytoplasm after karyokinesis is referred as cytokinesis.
● Cytokinesis begins in anaphase and ends in telophase.
● Mechanism of cytokinesis in animals and plants cell vary, in former it is
completed by cleavage and in latter by cell plate formation.
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13. The_Cell_Cycle_Shiven_Trambadia
Meiosis
● Farmer and Moore, explained that a specialized cell division in which number
of chromosomes is reduced to half is
● This reduction in chromosome number is achieved by one round of DNA
replication, followed by two rounds of chromosome segregation with no
intervening rounds of DNA replication.
● Meiosis is divided into two parts, meiosis I and meiosis II. At the end of
meiotic process, there are four daughter cells, each having half the total
number of chromosomes as parent cell.
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14. The_Cell_Cycle_Shiven_Trambadia
Meiosis
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15. The_Cell_Cycle_Shiven_Trambadia
Meiosis 1
● Prophase 1 of meiosis 1 is divided into five sub-stages: Leptotene,
Zygotene, Pachytene, Diplotene and Diakinesis.
● Leptotene: although each chromosome has replicated and consists of two
sister chromatids, these chromatids are unusually closely apposed, and each
chromosome therefore appears to be single.
● In leptotene to zygotene transition, the tips of the chromosomes move until
most end up in a limited region near each other, this arrangement is called a
Bouquet stage.
● It facilitates homologous chromosome pairing and synapsis.
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16. The_Cell_Cycle_Shiven_Trambadia
Zygotene
● As soon as the intimate pairing, between the two homologs initiates it marks
the starting of Zygotene.
● Synapsis often starts when the homologous end of the two chromosomes are
brought together on the nuclear envelope and proceeds inward in a zipper
fashion from both ends.
● Each pair of homologous chromosomes forms as a result of synapsis is called
a bivalent.
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17. The_Cell_Cycle_Shiven_Trambadia
Pachytene
● As soon as the synapsis is completed all along the chromosomes, the cells
are said to have entered the pachytene stage.
● The paired chromosomes now get shorten and thicken.
● At this stage , large recombination nodules appear at the intervals on the
synaptonemal complexes.
● Crossing over is a reciprocal exchange of equal and corresponding segment
between non-sister chromatids in a pair of homologous chromosome.
● It leads to the recombination of genes present on two homologous
chromosomes.
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18. The_Cell_Cycle_Shiven_Trambadia
Diplotene
● Desynapsis begins in the diplotene stage of meiotic prophase 1.
● Synaptonemal complex dissolves, allowing the two homologous
chromosomes in a bivalent to pull away from each other to some extent.
● But, each bivalent remains attached by one or more chiasmata.
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19. The_Cell_Cycle_Shiven_Trambadia
Diakinesis
● Diplotene merges imperceptibly into diakinesis, the stage of transition to
metaphase, as RNA synthesis ceases and the chromosomes condense,
thicken and become detached from the nuclear envelope.
● Now each bivalent consists of four separate chromatids, with each pair of
sister chromatids linked at their centromeres.
● Now cell enters Metaphase 1.
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20. The_Cell_Cycle_Shiven_Trambadia
Prophase 1 image
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21. The_Cell_Cycle_Shiven_Trambadia
Metaphase 1
● Breakdown of nuclear membrane and attachment of kinetochore microtubules
to bivalent, marks the initiation of Metaphase 1.
● Homologous pairs move together along the metaphase plate.
● Independent assortment is based on the physical orientation of chromosomes
of each bivalent along the metaphase plate, with respect to that of other
bivalents along the same equatorial line.
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22. The_Cell_Cycle_Shiven_Trambadia
Metaphase 1 to Anaphase 1
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23. The_Cell_Cycle_Shiven_Trambadia
Anaphase 1
● Homologous chromosomes are separated in Anaphase 1.
● Sister chromatids stay together.
● Special meiosis specific cohesin, Rec8 inhibits the separation of sister
chromatids.
● Homologous chromosomes separate and move to opposite poles. The
meiotic division is hence, called the reductional division, as it reduces the
chromosome number to half the diploid number in each daughter cell.
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24. The_Cell_Cycle_Shiven_Trambadia
Telophase 1
● As soon as the chromosomes arrive at the
poles meiosis 1 is said to have been ended
effectively.
● Now each daughter cell has half the number
of chromosomes left, with a pair of
chromatids.
● New nuclear membrane surrounds each
haploid set.
● Chromosomes are uncoiled back to
chromatin.
● Cytokinesis take place, generating two
daughter cells. 24

25. The_Cell_Cycle_Shiven_Trambadia
Meiosis 2
● Time gap between Meiosis 1 and Meiosis 2 is called interkinesis.
● It is usually short or may not occur at all, at this stage no DNA replication
occurs.
● Meiosis 2 is similar to that of Mitosis.
● But, no S phase occurs during Meiosis 2.
● Now the chromatids of each chromosome are not identical due to
recombination taken place in prophase 1 of meiosis 1.
● Meiosis 2 separates the sister chromatids producing two daughter cells each
with a haploid chromosome number.
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26. The_Cell_Cycle_Shiven_Trambadia
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27. The_Cell_Cycle_Shiven_Trambadia
Than yo !!!
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