Download Introduction 3 Types of Cell Division Binary fission Binary

Cell Cycle and Mitosis
• 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 a.k.a. Cell Reproduction Biology is the only subject in
which multiplication is the same
thing as division
3 Types of Cell Division
Type of Cell Division
Type of Cells it occurs in
Binary Fission
Prokaryotes
Asexual Reproduction
Mitosis
Eukaryotes
Asexual Reproduction
Growth of Individual
Repair/Maintenance of Tissues
Meiosis
Eukaryotes
Sexual Reproduction
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
Introduction
Function
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.
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! Eukaryotes Use Mitosis to Generate Identical Daughter Cells
• 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)
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The Cell Cycle
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
• 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
– cell doing its “everyday
job”
– cell grows
• S = DNA Synthesis
– copies chromosomes
• G2 = 2nd Gap
– prepares for division
– cell grows
– produces organelles, proteins, membranes
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. Each strand of chromatin is a decondensed chromosome • Chromatin is further compacted during mitosis to form condensed chromosomes
DNA during Interphase
DNA during Mitosis
http://www.hhmi.org/biointeractive/dna‐packaging
The Karyotype Describes All
the 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 Organization of Genetic Material
One
Chromosome
• 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
Karyotypes Before and After S‐phase of Cell Cycle
Before S‐Phase After S‐Phase 2
Karyotype of The Human Genome
Let’s not get Chromosomes, Homologous Chromosomes, and Sister Chromatids Confused!!
Homologous Chromosomes
Copied Homologous Chromosomes
• This is part of a karyotype looking at just chromosome 1
Sister Chromatids Prophase
• 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
Anaphase
• 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
4 Stages of Mitosis:
Prophase
Metaphase
Anaphase
Telophase
Video
Metaphase
• 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
Telophase
• 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
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Cytokinesis in Animal Cells
• Not considered a phase in mitosis
• Follows telophase
• The cell membrane moves inward to create two daughter cells
• Occurs at the metaphase plate
How can you remember the order???? • Answer this question....Where would you like your cat or dog to pee?
• On a PMAT of course Cytokinesis in Plant 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
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 What is this condition does not stop at a called?
checkpoint?
Some people love mitosis a little too much!
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