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CHAPTER 12 NOTES
Mitosis & Cell Cycle
Introduction

Genome – entire set of genetic information
 Genetic
information = DNA
 DNA is organized into chromosomes
 Chromosomes


= DNA + Histone proteins
Diploid – 2 sets of chromosomes
Haploid – 1 set of chromosomes
 Half
the number of chromosomes as diploid
Transcriptome & Proteome

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Transcriptome – set of all the mRNA produced by a
cell or an organism
Proteome – entire set of proteins coded for by the
genome of a cell or an organism
DNA  RNA  Protein
Genome  Transcriptome  Proteome
Vocabulary


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Cell Cycle – life of a cell from formation until
division or death
Mitosis vs. Meiosis
Every somatic (Body) cell is a clone of the zygote
 BUT
the zygote is formed from union of cells
 Each of which was produced by Meiosis (gametes)

Only cells that are not clones are gametes
 Male
= sperm
Female = egg cells
Questions

Which cells arose from Mitosis? (Diploid)
 All
cells except gametes
 Called somatic cells

Which cells arose from Meiosis? (Haploid)
 Only
sperm in males (spermatogonia)
 Only egg cells in (oogonia)
 Called gametes
Cell Cycle
Cell Cycle Notes

G1 – Cell growth
 Cells
do their cell things
 Vast majority of time in the cell cycle
 Human cell = 46 chromosomes

S – Chromosomal duplication
 Human
cell = 46*2 = 92 chromosomes
 Cells still grow during this time

G2 – Second Gap
 Brief

period between S and Mitosis
Mitosis / Cytokinesis
Mitosis
Mitosis Notes by chromosomes

Interphase (G2) = 2x DNA as usual
 Call

it 92 DNA units (2*46 = 92 = Chromosomes)
Prophase/Metaphase = 2x DNA as usual
 BUT
same number of chromosomes
 Each chromosome = 2 chromatids
 Chromatids are copies of each chromosome
 Chromosomes = 92 DNA units
 2 sets of Chromatids = 2 *46 = 92 DNA units
Mitosis Notes (Page 2)

Anaphase/Telophase = 1x DNA as usual
 Chromatids
separate
 Now the chromatids are called “Daughter chromosomes”
 Each cell has ½ the DNA units
 ½ of 92 DNA units (Metaphase) = 46 DNA units
 So each daughter cell has 46 DNA units
 Each
parent cell has 46 DNA units
Chromatin, Chromatids, & Chromosomes

Chromatin – diffuse form of DNA + Protein

Chromosomes – condensed form of DNA + Protein

Chromatids – 2 chromatids are attached at the
centromere
2
copies of the same chromosome
 Each chromatid  Daughter chromosome at Anaphase
Cell Cycle Regulation


Cell cycle control system
Some cells divide
 Continuously
(skin cells)
 Occasionally (liver cells)
 Never (CNS cells & muscle cells)

Signals to divide are present in cytoplasm
 These
signals control the rate of cell division
 Result of signal transduction pathways
Checkpoints

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Control points of cell cycle
Cell cycle is controlled by a
series of checkpoints
 Tell
cell to stop or go through
cellular division
 G1 phase checkpoint
 G2 phase checkpoint
 M phase checkpoint
G1 Checkpoint “Restriction”

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Most important checkpoint in
mammalian cells
If G1 is successful, then G1, S,
G2, and M go ahead
If NOT, then G0 stage
 G0
is called the nondividing
stage
 Independent of cell cycle
 Most cells in the body are in G0
Protein kinases & Cyclins

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Regulatory molecules for cell cycle
What do protein kinases do?
Protein kinases give the “Go ahead” signal @ G1 &
G2 checkpoints
Most protein kinases are inactive
 Activated
by cyclins (cyclical fluctuating protein)
 Called cyclin-dependent kinases (Cdk)
Maturation Promoting Factor (MPF)

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Example of a Cdk + cyclin interaction
Signal that allows cell to pass through G2 into
mitosis
Can be thought of as “Mitosis Promoting Factor”
Normal cells…

Density Dependent Inhibition
 Crowded
cells cease mitosis
 Binding of a cell surface protein to its counterpart on an
adjoining cell = growth-inhibiting signal for both cells

Anchorage Dependency
 In
order to divide, cells must be attached to a substratum
 Substratum = ECM or other load-bearing material
Cancerous Cells
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Do NOT adhere to normal cell signals
Divide excessively
Violate density-dependent inhibition & anchorage
dependency
Considered “immortal cells”
Normal cells undergo a process of genetic
alteration that affects cell cycle regulation
 Called
transformation
It’s not a tumor…

Tumor = mass of abnormal cells
 Abnormal

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because?
Benign tumor – abnormal cells that remain at the
original site
Malignant tumor – abnormal cells impair functions
of one or more organs
Cancer = malignant neoplasm (tumor)

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Malignant tumors are characterized by anaplasia,
invasiveness, & metastasis
Anaplasia – reversion of differentiation
Invasiveness – Intrusion into and destruction of
surrounding tissues
Metastasis – spread of neoplasms via blood vessels
to distant tissues or organs