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Unit 4 Notes – Cell Growth and Mitosis
Name: ___________________________________________
Cell growth
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In most cases, a living thing grows because it produces more cells.
Cell growth is controlled
More cells = a larger organism
Limits of cell growth
I. Surface-to-volume ratio
 Is greater in small cells than in larger cells
 A greater surface area allows materials to enter and leave the cell at a faster rate
II. DNA’s ability to produce enough messenger RNA decreases with an increase in cell growth
 The cell must either divide or die
Rates of cell growth
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Rates differ from cell type to cell type
Are affected by external conditions
 The conditions have to be right
Certain cells, such as in the heart and the nervous system rarely divide, if at all.
Cells of the skin & digestive tract grow & divide rapidly due to daily wear & tear.
Cells grow until they come into contact with other cells.
Cell growth & cell division are turned on and off to repair injuries.
Uncontrolled cell growth
CANCER: a disorder in which some cells have lost the ability to control their own rate of growth (often
the result of alterations of the DNA sequence AKA mutations)
 Cancer cells do not stop growing when they come in contact with other cells
DNA
Chromatin: Long strands of DNA wrapped around proteins called histones
 Present during interphase of the cell cycle
 During the early stages of mitosis, the chromatin condenses & the chromosomes are visible
Chromosomes: Condensed genetic information (DNA) that is passed on from one generation of cells
to the next.
 Are not visible in cells except during mitosis.
Sister chromatids: 2 identical DNA parts resulting from DNA replication
Centromere: Holds the 2 sister chromatids together
 In mitosis, spindle fibers attach here to separate the sister chromatids.
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Unit 4 Notes – Cell Growth and Mitosis
Name: ___________________________________________
Cell cycle
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Unit 4 Notes – Cell Growth and Mitosis
Name: ___________________________________________
Interphase
 Interphase is not part of mitosis!!
 Longest part of the cell cycle
 Consists of G1, S, and G2, phases
 prepares cell for mitosis by growing & reproducing genetic material (DNA)
Cell cycle
 G1: Repair & growth of cell
 S: DNA replication occurs
 G2: Organelles duplicate
 If things didn’t happen perfectly apoptosis (cell death) occurs
 M: Cell divides
 G0: Cell “rests”
Mitosis
Mitosis: The process by which a cell produces an identical copy of itself for repair & growth
Parent cell
Daughter cells
Prophase
 1st and longest phase of mitosis
 Chromatin (DNA) condenses to form chromosomes
 Centrioles & spindle fibers appear
 Nucleolus & nuclear envelope vanish
Metaphase
 2nd and shortest phase of mitosis
 Chromosomes align at the equator
 Spindle fibers attach at centromeres & centrioles
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Unit 4 Notes – Cell Growth and Mitosis
Name: ___________________________________________
Anaphase
 3rd phase of mitosis
 Centromeres that join the sister chromatids split causing the
sister chromatids to separate and become individual
chromosomes
 Each chromosome is pulled toward the centrioles by the
spindle fibers
Telophase
 Last phase of mitosis
 Chromosomes unravel into chromatin
 Nuclear envelopes form around the chromatin sets
 Spindle fibers to break apart, and a nucleolus becomes
visible in each daughter cells nucleus
Cytokinesis: Division of the cytoplasm into 2 cells
 Last step of telophase
Animals: A cleavage furrow is formed and the parent cell pinches into 2 identical daughter cells
Plants: A cell plate is formed halving the cell. A cell wall replaces the cell plate creating 2 identical
daughter cells.
Where does mitosis occur?
I. Unicellular organisms: it is their method of reproduction
II.Multicellular organisms: it is used to repair damaged tissue or replace cells and for growth in body
cells (not for gametes – sex cells)
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1 organism
2 organisms
II.
Parent cell
Daughter cells
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