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Cell Division

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by

Lainey Molin

on 4 February 2015

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Transcript of Cell Division

Cell Division
Why can't cells grow indefinitely?
DNA Overload
Each cell contains one set of DNA
As the cell grows, the DNA cannot meet all of the cell's needs
Exchange of Materials
Rate of material exchange depends on
surface area to volume ratio
Process by which a cell divides to form two
daughter cells
Increases surface area to volume ratio
DNA replicates prior to cell division
Cell Division
Under normal circumstances, DNA takes the form of chromatin
Before cell division, chromatin coils up and condenses to form visible chromosomes
Chromosomes replicate before cell division to form two
sister chromatids
that are joined in the center by a protein called a
centromere
G1 Phase
– increase in size of the cell, synthesis of organelles and proteins
S Phase
– DNA replication
G2 Phase
– (shortest of interphase) organelles and molecules required for cell division are made
Events that occur between cell divisions
Mitosis
– division of the nucleus of a cell
Cytokinesis
– division of the cytoplasm of a cell
Chromosomes visible
Centrioles to opposite sides
Centrioles form the
Spindle Fibers

Prophase
Chromosomes attach to spindle via centromeres
Nucleolus & nuclear envelope break down
Chromosomes line up in center of the cell
Metaphase
Centromeres split
Chromosomes move toward the poles of the cell, one sister chromatid from each pair on each side
Anaphase
Telophase
Chromatin reforms
Nuclear envelope reforms around each group of chromosomes
Spindle breaks apart
Nucleolus reappears in each daughter nucleus
Usually occurs during telophase but is
not considered part of telophase

In plants, a
cell plate
forms
Cells stop growing when they come into contact with other cells
If you remove some of the cells, they will start growing again!
Cell Division Controls
When a protein is inserted into a non-dividing cell, a spindle forms!
Cyclins
– regulate the timing of the eukaryotic cell cycle
Apoptosis
- programmed cell death
Cancer
– condition in which cells are unable to control growth, resulting in masses of cells (
tumors
)
Causes of Cancer:
Smoking
Exposure to radiation
Viral infection
Stem Cells
Unspecialized cells that differentiate into various other cell types
Drosophila has 8 total chromosomes
4 from mother
and
4 from father
Homologous Chromosomes
each chromosome from the father corresponds to one from the mother
Each is the same set of genes, just different
alleles
1 of each homologous chromosome (N)
Both homologous chromosomes (2N)
Body cells are diploid
Gametes are haploid
Meiosis is a form of reduction division
The number of chromosomes per cell is cut in half by
separating homologous chromosomes
Tetrad
each set of replicated chromosomes pairs with its corresponding homologous chromosomes
Crossing Over
Exchange of alleles between homologous chromosomes to form new combinations
Each daughter cell has
half
the number of chromosomes as compared to original parent cell
*DNA does not replicate a second time!
Full transcript