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THE CELL CYCLE: CELL DIVISION BY
MITOSIS
CH 12
In order for life to continue, cells
must reproduce
https://www.youtube.com/watch?v=
mx8itzrdV7I
I. Overview of cell division
• In unicellular organisms cell division
produces new organism
• In multicelled organisms cell division
produces new cells for growth, repair, and
development from fertilized egg
• Most cell divisions produce identical cells
• Only meiosis produces egg and sperm (ch 13)
II. Organization of Cellular Genetic
Material
• Genome: the cell’s DNA
• DNA molecules are organized into
chromosomes
• Prokaryotic genomes: single circular DNA
• Most eukaryotic genomes: many linear DNA
strands with associated histone proteins
• Eukaryotic chromosomes are called
chromatin that coil to fit in the nucleus
III. The Cell Cycle
• Consists of 2 phases:
o Interphase: G1, S, G2
o Mitotic phase: mitosis and cytokinesis
A. Interphase
• G1: cell grows to critical size
• S: DNA is replicated forming identical sister
chromatids held at centromere. Centromere has a
kinetochore where spindle proteins attach
• G2: cell prepares to divide
B. Mitotic Phase
Consists of
• Mitosis (nuclear division)
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
• Cytokinesis (division of cytoplasm)
C. Mitotic Spindles and Mitosis
• Made of microtubule protein,
centrosomes(in animal cells), and aster
• Centrosome is microtubule organizing
center and is where microtubules form
• Centrosome replicates and both move to
opposite sides of cell
• Spindle microtubules from both
centrosomes eventually attach to
kinetochore to help move and separate
chromatids
D. Role of spindles in mitosis
• During prometaphase, spindle microtubules
attach to kinetochore and begin to move
chromosomes
• During metaphase, the spindle microtubules
align chromosomes in center of cell
• During anaphase, spindle microtubules
depolymerize and shorten, separating sisters
• During telophase genetically identical nuclei
form and mitotic spindle breaks down
Cytokinesis is the division of the cytoplasm and
begins during anaphase/telophase
• In animal cell cleavage furrow forms pinching cell
in two
• In plant cells cell plate forms in center building
cell wall and membrane to separate cells
IV. Bacterial Cell Division
• Chromosome replicates and two chromosomes
move apart
• Cell divides
IV. Control of the Cell Cycle
A. Cell cycle checkpoints
1. cells will only divide when new cells are
needed: contact inhibition
• Uncrowded cells release growth factors
that stimulate cell division
• crowded cells don’t divide. No growth
factors produced
• Cancer cells don’t follow contact inhibition
• Always produce growth factors
• Overexpress growth factor receptors
• Have mutations that allow them to grow
without growth factors
2. Cell division will proceed if identical cells will
be produced
– DNA must be replicated correctly
– There must be enuf telomeres at the ends of the
DNA
– The spindles are attached to kinetochores
correctly
3. There are 3 checkpoints:
4. Cyclin and cyclin dependent kinases regulate
the cell cycle
• Cyclin levels fluctuate during cell cycle
• In order for mitosis to proceed, cyclin
dependent kinases must bind cyclins forming
mitosis promoting factor