Download Ch 12 Cell Cycle

Chapter 12
The Cell Cycle

In unicellular organisms, division of one cell
reproduces the entire organism

Multicellular organisms depend on cell division for:
Development from a fertilized cell
 Growth
 Repair

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Cell division results in genetically
identical daughter cells
•
Most cell division (mitosis) results in daughter cells
with identical genetic information, DNA
•
A special type of division (meiosis) produces
nonidentical daughter cells (gametes, or sperm
and egg cells)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Cellular Organization of the
Genetic Material

All the DNA in a cell constitutes the cell’s
genome

A genome can consist of
a single DNA molecule (prokaryotic cells)
 a number of DNA molecules (eukaryotic cells)


DNA molecules in a cell are packaged into
chromosomes
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Every eukaryotic species has a characteristic
number of chromosomes in each cell nucleus

Somatic cells (nonreproductive cells) have two
sets of chromosomes

Gametes (reproductive cells: sperm and eggs)
have half as many chromosomes as somatic cells

Eukaryotic chromosomes consist of chromatin, a
complex of DNA and protein (histones).
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Distribution of Chromosomes
During Eukaryotic Cell Division

Each duplicated chromosome has two sister
chromatids, which separate during cell division

The centromere is where the two chromatids are
most closely attached
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 12-4
0.5 µm
Chromosomes
Chromosome arm
DNA molecules
Chromosome
duplication
(including DNA
synthesis)
Centromere
Sister
chromatids
Separation of
sister chromatids
Centromere
Sister chromatids

Eukaryotic cell division consists of:
Mitosis, the division of the nucleus
 Cytokinesis, the division of the cytoplasm


Gametes are produced by a variation of cell
division called meiosis

Meiosis yields nonidentical daughter cells that
have only one set of chromosomes, half as many
as the parent cell
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Phases of the Cell Cycle

The cell cycle consists of

Interphase (cell growth and copying of chromosomes
in preparation for cell division)
G1 phase- cell grows
 S phase- chromosomes duplicate
 G2 phase- cell grows/prepare for division


Mitotic (M) phase
mitosis
 cytokinesis

Video: MITOSIS
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 12-UN1
G1
S
Cytokinesis
Mitosis
G2
MITOTIC (M) PHASE
Prophase
Telophase and
Cytokinesis
Prometaphase
Anaphase
Metaphase

Mitosis is conventionally divided into five phases:

Prophase

Prometaphase
Metaphase
 Anaphase
 Telophase


Cytokinesis: (division of cytoplasm)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
PROPHASE




Chromatids condense and
become visible
Nucleoli dissapears
Centrosomes (pair of
centrioles) move to the poles
Spindle begins to form
PROMETAPHASE



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Nuclear envelope breaks
Microtubules form from
centrosome and move toward
the middle of cell
Sister chromatids have a
kinetochore (specialized
protein located on centromere)
Spindle attach to kinetochore
METAPHASE



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Longest stage of mitosis
Spindle is completely
formed
Spindle attaches to
kinetochore of
chromatids
Spindle moves
chromatids to middle of
cell (metaphase plate)
ANAPHASE

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Shortest stage of Mitosis
Spindle pulls sister chromatids apart (become
chromosomes)
Chromosomes are pulled toward the poles
Spindle shortens and cell elongates
Chromosomes reach poles
TELOPHASE



Nuclear envelopes reappear
Spindle dissappears
2 identical nuclei and 1
cytoplasm
Video: MITOSIS
Cytokinesis: A Closer Look
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Division of cytoplasm
In animal cells, cytokinesis occurs by a process
known as cleavage, forming a cleavage furrow
In plant cells, a cell plate forms during cytokinesis
Vesicles
forming
cell plate
Cleavage furrow
Wall of
parent cell
New cell wall
Cell plate
Contractile ring of
microfilaments
Daughter cells
(a) Cleavage of an animal cell (SEM)
Daughter cells
(b) Cell plate formation in a plant cell (TEM)
The Cell Cycle Control System

The sequential events of the cell cycle are directed
by a distinct cell cycle control system, which is
similar to a clock

The clock has specific checkpoints where the cell
cycle stops until a go-ahead signal is received
Video: CELL CYCLE
Video: CONTROL SYSTEM CELL CYCLE
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
G1 checkpoint
Control
system
G1
M
G2
M checkpoint
G2 checkpoint
S
•
•
Cell receives a go-ahead signal at the G1 checkpoint, it will
usually complete the S, G2, and M phases and divide
Cell does not receive the go-ahead signal, it will exit the cycle,
switching into a nondividing state called the G0 phase
G0
G1 checkpoint
G1
Cell receives a go-ahead
signal
G1
Cell does not receive a
go-ahead signal
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings