The Cell Cycle

1
The Cell Cycle
Brittany Amanda Biology 9/23/03
2
Overview

• G1 phase
• S phase
• G2 Phase
• Mitosis
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis
• Meiosis

In this presentation, all of the phases of the
cell cycle will be covered. We will start with
the G1 phase and continue until the last phase of
the cycle. The order is as follows
3
G1 Phase

• Sometimes called Interphase.
• The formation of two daughter cells from a
  parent cell in
• cytonkinesis is an energy-consuming process.
  The time
• needed by the new cells to replenish their
  energy
• causes this gap.
• After cell energy reserves are restored, the
  daughter
• cells begin to grow.
• This is the longest phase of the cell cycle.

4

• Synthesis means to make.
• After a period of growth, each cell's original
  DNA
• is duplicated in the process of replication or
  the
• process of duplicating the DNA molecule.

S Phase
This is a chromosome that is found in the cell
during cell division.
S PHASE IS ALSO KNOWN AS THE SYNTHESIS PHASE OR
DNA SYNTHESIS.
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• During the G2 Phase, the cell again
• undergoes growth and protein synthesis
• because it needs enough proteins for the 2
• cells it will split into, priming it to be able
  to
• divide. Once this is complete, and has gone
• through many checkpoints along the way, the
• cell finally enters the fourth and final phase
  of
• the cell cycle. This phase is known as the M
• (Mitosis) phase.

• The replication of DNA is another
  energy-consuming process
• for the cell. The time taken by a cell to
  build up its energy
• reserves produces this second "gap".

G2 Phase
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Mitosis

• Mitosis is the process by which DNA is divided
  into two identical daughter sets before the cell
  divides.
• There are four stages that occur before the cell
  is completely split apart. They are
• Prophase Anaphase
  Metaphase Telophase

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Prophase

• Early prophase chromatin coils to form
  chromesomes,
• nuclear membrane disappears, and centrioles
  migrate to
• opposite poles of the cell.
• Middle prophase spindle fibers, microtubules of
  protein,
• begin developing.
• Polar fibers extend across the cell from
• centriole to centriole.
• Kinetiochore fibers extend from the
• centromeres of a chromosome to the centrioles.
• Late prophase protein fibers called asters
• radiate from each centriole in animal cells.

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• In this phase, kinetochore fibers move the
  chromosomes
• to the equator of the cell.

Movement taking place during metaphase.
Metaphase

• Each chromosome has reached its maximum density.
  
• The homologous pairs and their sister chromatids
  interact
• with fibers which form from either side of the
  nuclear
• envelope of the cell. These fibers are
  procudes from the
• centriole. There is a centriole at the
  opposite ends of the cell.
• The chromosomes are then lined by the fibers at
  what is
• known as the metacentric plate, which is
  located in the
• center.

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• Pulls apart the tetrad,
• separating each
• homologous chromosome.
• The centromere of each
• pair of chromatids divides,
• the chromatids separate
• and are pushed to opposite
• poles of the cell by the
• combined efforts of the
• fibers, all in one quick
• motion.

The separation of the fibers to opposite poles.
Anaphase
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• All fibers disappear.
• Chromatids unwind and stretch to form
• chromatin.
• A nuclear membrane forms around each
• mass of chromatin, splitting the cytoplasm
• into two separate parts.
• Then interkinesis will follow, which is a
• resting period.

Telophase
Membranes forming, showing the division of the
cytoplasm.
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Cytokinesis

• The division of the cytoplasm of a parent cell.
• (the cell pinches together in the center)
• While each daughter cell gets identical sets of
• DNA, the cytoplasm and organelles are only
• roughly divided equally between the two cells.

Detailed events occurring in cytokinesis.
THE FINAL STAGE OF MITOSIS
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Meiosis

• Meiosis I -
• DNA replication takes place.
• A parent cell produces two daughter
• cells with one member of each original
• pair of homologous chromosomes.

• Meiosis II -
• There is no DNA replication.
• The chromatids of each chromosome
• separate and each daughter cell divides.
• At the end of Meiosis, there are four
• daughter cells from each parent cell. Each
• daughter cell has half the number of
• chromosomes of the parent.

The process of Meiosis is more complicated than
the single division of Mitosis because it
provides more opportunity for genetic variation.
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Conclusion

• Covered in this presentation was the cell cycle
  in detail. It was learned that the steps within
  this cycle are
• G1 phase - energy consuming process.
• S phase - DNA duplication.
• G2 Phase - growth and energy synthesis.
• Mitosis - equal division of DNA.
• Prophase - 2 centrosome move to opposite poles.
• Metaphase - chromosomes move to equator of cell.
• Anaphase - fibers separate to opposite poles.
• Telophase - nuclear membrane forms around the 2
  cells.
• Cytokinesis - division of the cytoplasm and
  organelles.
• Meiosis - two divisions in sequence.

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Works Cited
Cells and the Cell Cycle - Day 3. 2003. Desert
Vista High School. 24 September 2003.
lthttp//staff.tuhsd.k12.az.us/gfoster/standard/bc
ell2.htmgt Cell Cycle Regulation. 2003.
University of Pennsylvania lthttp//www.geocities.
com/CollegePark/Lab/1580/cycle.htmlgt Metaphase
I. 1997. North Carolina State University
lthttp//www4.ncsu.edu/unity/users/b/bnchorle/www/
metai.htmgt Anaphase I. 1997. North Carolina
State University lthttp//www4.ncsu.edu/unity/user
s/b/bnchorle/www/anai.htmgt Telophase I. 1997.
North Carolina State University
lthttp//www4.ncsu.edu/unity/users/b/bnchorle/www/
teloi.htmgt CYTOKINESIS. 1999. The University
of Manchester lthttp//www.teaching- biomed.man.ac.
uk/ramsay/Cytok.htmgt Meiosis. 1999. National
Health Museum lthttp//www.accessexcellence.org/AB
/GG/meiosis.htmlgt