Download The Cell Cycle - Warren County Schools

The Cell Cycle
Cell Division
• Cell Division
– Cells divide in order for us to grow
– As a cell grows, its volume increases more rapidly
than its surface area
– When the surface area-to-volume ratio is too small,
the cell cannot move materials in and out of the cell at
a sufficient rate or in sufficient quantities.
– Why are we made of millions of small cells
instead of just one big cell?
Surface Area to Volume Ratio
Length of
side
100 cm
10 cm
1 cm
0.1 cm
Surface
Area
Volume
SA:Volume
Ratio
3 Phases of the Cell Cycle
• Interphase
– G1
– S phase
– G2
• Mitosis
– Prophase
– Metaphase
– Anaphase
– Telophase
• Cytokinesis
Cell Life Span
CELL TYPE
Skin Cell
APPROXIMATE LIFE
SPAN (Time Spent in
Interphase)
2 weeks
Red Blood Cell
4 months
Liver Cell
300-500 days
Intestine—internal lining
4-5 days
Intestine—muscle and
other tissues
16 years
Purpose of the Cell Cycle:
• To make 2 genetically identical
daughter cells from a single
parent cell
Interphase
• The "holding" stage
or the stage between
two successive cell
divisions.
• Some 90 % of a
cell's time in the
normal cell cycle may
be spent in this
phase
C = chromatin
I = nucleolus
Cell Cycle
INTERPHASE
G1 phase
S phase
G2 phase
The cell grows
The DNA replicates
The cell prepares to
divide
Interphase
Gap 1 (G1)
• Cell carries out its normal
cell functions
• Cell increases in size
(grows)
• Organelles increase in
number
• A cell spends most of its
time in this stage,
although the length of
time varies by cell type.
Interphase
Synthesis (S)
• Synthesis—combining of
parts to make a whole
• Cell makes a copy of its
DNA (nucleus)
• By the end of the S stage,
the cell nucleus contains
two complete sets of DNA
Interphase
Gap 2 (G2)
• Additional growth occurs
• Checkpoint—everything must be in order
before the cell can move on and go
through mitosis and then cell division
Mitosis (M Stage)
• Mitosis—division of
the cell nucleus and
its contents
• Nuclear membrane
dissolves
• The duplicated
DNA condenses
• Two new nuclei
form
Mitosis
Prophase
• Loose chromatin
condenses into
tightly coiled
chromosomes
• The nuclear
envelope breaks
down
• Centrioles begin to
move to the opposite
poles and spindle
fibers form
Condensing of Chromosomes
• One chromosome = one continuous strand of
DNA
• DNA wraps around proteins called histones,
forming chromatin
• Chromatin compacts further, forming a chromatid
• Two identical chromatids are called sister
chromatids
• Sister chromatids are held together at the
centromere
• Telomeres are located at the ends of the
chromatids
• Humans have 23 pairs of chromosomes (46 total)
Sister Chromatids
Telomeres—regions of
repetitive DNA at the end of
a chromosome, which
protects the end of the
chromosome from
destruction
Progeria
Mitosis
Metaphase
• Spindle fibers
attach to each
chromosome
• Sister chromatids
are aligned along
the equator by the
spindle fibers
• In humans, 46
sister chromatids
line up in the
middle of the cell
Mitosis
Anaphase
• Chromatids
separate to
opposite sides of
the cell
• Pulled by spindle
fibers
Mitosis
Telophase
• A complete set of
identical chromosomes
is positioned at each
pole of the cell
• The nuclear
membranes start to
form
• Chromosomes begin to
uncoil
• Spindle fibers fall apart
Cytokinesis
• Cytokinesis—
division of the
cytoplasm
• Results in two
daughter cells
• Both new cells are
genetically identical
to the original
parent cell
Cytokinesis Differs in Animal
and Plant Cells
• In Animal cells, the
membrane forms a
furrow and pinches
closed
• In Plant cells, the
membrane cannot pinch
inward because of the
cell wall. Instead, a cell
plate forms between the
two new nuclei
At the End of the Cell Cycle:
• Final Products are two identical cells
– Smaller in size (larger surface area to volume
ratio)
– Each new cell has 46 chromosomes
– Organelles get divided up between the two
cells during cytokinesis
• Not always exactly evenly divided
• The cell can make more organelles if needed