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Cell Cycle and Mitosis
a.k.a. Cell Reproduction
Biology is the only subject in
which multiplication is the same
thing as division
Introduction• All organisms start
with a single cell.• All new cells are
produced from other, already existing cells.
• Millions of cell divisions take place in our bodies every day to replace the cells that have died
Cell Type Approximate Life Span
Skin Cells 2 weeks
Red Blood Cells 4 months
Liver Cells 300-500 days
Intestine-internal lining 4-5 days
Intestine-muscles and other tissue 16 years
Source: Spaulding et al., Cell 122:1.
Type of Cell Division Type of Cells it occurs in Function
Binary Fission Prokaryotes Asexual Reproduction
Mitosis EukaryotesAsexual Reproduction Growth of Individual
Repair/Maintenance of Tissues
Meiosis Eukaryotes Sexual Reproduction
3 Types of Cell Division
Binary fission• Asexual reproduction of a Prokaryotic cell• Bacteria (Ex E. coli = every 20 minutes)
• How many bacteria will result from 1 bacteria 7 hours (optimal conditions)? 1 million!
Binary Fission• Begins with the
duplication of the genetic material
• A plasma membrane splits the cell in two, with each side containing a single copy of the DNA
• The resulting two daughter cells replace the single parent cell and are genetically identical
• Multiphase process in which the cell divides from 1 parent cell to 2 identical daughter cells.
• Occurs in all cells except reproductive cells
• Mitosis is how asexual cell are replicated.
• Meiosis is how sex cells are produced (we will look at this process later in the term)
Eukaryotes Use Mitosis to Generate Identical Daughter Cells
The Cell Cycle• Interphase is not part of mitosis!!• This is when the cell is doing its
“everyday” jobs and getting ready for mitosis
• Interphase is divided into 3 phases:
• G1 = 1st Gap– cell doing its “everyday
job”– cell grows
• S = DNA Synthesis– copies chromosomes
• G2 = 2nd Gap– prepares for division– cell grows– produces organelles, proteins,
membranes
• Many adult cells enter a non-dividing phase called G0
• The G0 phase can last from a few days to the lifetime of the organism
• Ex: liver cells stay in G0 for approximately a year, then reenter the cycle
The Cell Cycle
Organization of Genetic Material• For equal division of the DNA to
occur it has to be organized • In interphase each DNA double helix
is packaged with special proteins to form long strands of chromatin
• Chromatin is further compacted during mitosis to form
chromosomes
DNA Packaging
DNA during Interphase
DNA during Mitosis
Organization of Genetic Material
• DNA is replicated during S phase, resulting in two identical pieces of DNA, known as sister chromatids
• Each human cell has twice the usual amount of DNA at the end of S phase and the start of mitosis
• The identical sister chromatids are held together at a region called the centromere
One Chromosome
The Karyotype Describes Allthe Chromosomes in a Nucleus
• Every species has its own characteristic number of chromosomes
• The display of all the chromosomes in a somatic (non-sexual) cell is called the karyotype
• Each of us has two of each chromosome, one from mom and one from dad.
• This pair of chromosomes, one from mom and one from dad, are similar but not identical
• They are called homologous chromosomes
Karyotypes Before and After S-phase of Cell Cycle
Before S-Phase After S-Phase
Karyotype of The Human GenomeLet’s not get Chromosomes, Homologous Chromosomes, and Sister Chromatids Confused!!
• This is part of a karyotype looking at just chromosome 1
Copied Homologous
Chromosomes
Sister Chromatids
Homologous Chromosomes
ProphaseMetaphaseAnaphaseTelophase
Video
4 Stages of Mitosis:
• Beginning of mitosis• DNA compacts into
chromosomes• Centrosomes appear and
begin to move to opposite ends of cell making the poles of the cell
• The nuclear envelope breaks down
• The mitotic spindle forms. It is made up of microtubules attached to each centrosome
Prophase
• Sister chromatids attach to the spindle fibers at the centromere through the kinetochore
• The kinetochores are patches of proteins that attaches to the microtubules
• Each centromere has two kinetochores that attach to the spindle fibers, one from each centrosome
• This causes the chromosomes to line up on the metaphase plate
Metaphase
• Sister Chromatids separate and begin to move to opposite ends of the cell
• The centrosomes shorten the spindle fibers dividing the sister chromosomes and bringing them to opposite side of the cell
• Each chromatid is now considered a new chromosome
Anaphase
• Begins when the new chromosomes reach the centrosome
• The spindle fibers break down
• Two new nuclei form and the nuclear envelope forms around the chromosomes at each pole of the cell
• Chromosomes appear as chromatin
• After telophase cytokinesis occurs
Telophase
• Not considered a phase in mitosis
• Follows telophase• The cell
membrane moves inward to create two daughter cells
• Occurs at the metaphase plate
Cytokinesis in Animal Cells
• Since plants have cell walls they also have to build this between daughter cells.
• Vesicles containing cell wall components move to the metaphase plate where the cell wall forms
Cytokinesis in Plant Cells
How can you remember the order????
• Answer this question....Where would you like your cat or dog to pee?
• On a PMAT of course
The Cell Cycle Is Highly Regulated• Cells divide in response to
internal and external signals• In humans, cell cycle
regulatory proteins are activated by external signals to divide, advancing the cell from G1 to S phase and initiating DNA replication
• Cell cycle regulatory proteins can stop or pause the cell cycle if conditions are not favorable for cell division
What happens when the cell does not stop at a checkpoint?
What is this condition called?
Cancer 6 key mutations• Turn on cell division
– Turn on promoter genes• Ignore checkpoints
– Turn off suppressor genes• Avoid programed cell death
– Turn off “suicide” genes• Unlimited divisions
– Turn on chromosome maintenance genes• Promotes blood vessel growth
– Turn on blood vessel genes• Cell attachment, anchor and density dependence genes
– Turn off touch censor gene
Some people love mitosis a little too much!
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