5.1
The Cell Cycle
The student is expected to:
5A describe the stages of
the cell cycle, including
deoxyribonucleic acid (DNA)
replication and mitosis, and the
importance of the cell cycle to the
growth of organisms
TEKS 5A
5.1
The Cell Cycle
TEKS 5A
KEY CONCEPT
Cells have distinct phases of growth, reproduction,
and normal functions.
5.1
The Cell Cycle
The cell cycle has four main stages.
• The cell cycle is a regular pattern of growth, DNA
replication, and cell division.
TEKS 5A
5.1
The Cell Cycle
TEKS 5A
• The main stages of the cell cycle are gap 1, synthesis, gap
2, and mitosis.
– Gap 1 (G1): cell growth and
normal functions
– DNA synthesis (S): copies
DNA
– Gap 2 (G2): additional
growth
– Mitosis (M): includes
division of the cell nucleus
(mitosis) and division of the
cell cytoplasm (cytokinesis)
• Mitosis occurs only if the cell is large enough and the DNA
undamaged.
5.1
The Cell Cycle
Cells divide at different rates.
• The rate of cell division varies with the need for those
types of cells.
• Some cells are unlikely to divide (G0).
TEKS 5A
Limits to cell growth
1. DNA “overload”: The larger a
cell becomes, the more
demands the cell places on its
DNA.
a) DNA stores the information that
controls body functions
b) When a cell is small, DNA can
easily control the cell’s
functions and meet its needs.
c) When a cell is large, it still only
has one copy of DNA, so it is
more difficult for the cell to
perform its functions.
Limits to cell growth
2. Exchanging materials:
• Large cells have more trouble moving
substances across the cell membrane.
• If a cell is too large, it is difficult to get
enough oxygen and nutrients in and waste
products out
Division of the Cell
When a cell gets too large, it :
1. makes a copy of its DNA (replication),
and then…
2. divides to form two “daughter” cells.
5.1
The Cell Cycle
Cell size is limited.
• Volume increases faster than surface area.
TEKS 5A
Surface area to volume ratios
6
1
• 1 X 1 X 1 cube SA:______
volume: _____
8
24
• 2 X 2 X 2 cube SA:______
volume: _____
600
1,000
• 10X10X10 cube SA:______
volume: _____
• So when volume doubles, the surface area
cannot “keep up” with it
5.1
The Cell Cycle
• Surface area must allow for adequate
exchange of materials.
– Cell growth is coordinated with
division.
– Cells that must be large have
unique shapes.
TEKS 5A
5.2
Mitosis and Cytokinesis
The student is expected to:
5A describe the stages of
the cell cycle, including
deoxyribonucleic acid (DNA)
replication and mitosis, and the
importance of the cell cycle to the
growth of organisms
TEKS 5A
5.2
Mitosis and Cytokinesis
KEY CONCEPT
Cells divide during mitosis and cytokinesis.
TEKS 5A
Before a cell gets too big, it will
divide to form two “daughter
cells”
Before a cell divides, it makes a
copy of its DNA for each
daughter cell.
Cell Division
1. Cell division in eukaryotes is more complex than in
prokaryotes.
2. There are two stages of eukaryotic cell division
a. Mitosis: Division of the cell nucleus
b. Cytokinesis: Division of the cell cytoplasm
3. Unicellular organisms
reproduce asexually
by mitosis or
something similar to
mitosis (prokaryotes
cant do mitosis!)
a. The daughter cells
are identical to the
parents cells
Asexual Reproduction
•
•
Is one cell reproducing by itself
Two types:
1. Binary Fission: organism replicates its DNA and
divides in half, producing two identical daughter
cells
• Example: bacteria
2. Budding: asexual process by which yeasts
increase in number
Budding
Binary Fission
Chromosomes
1. Chromosomes are made of condensed
chromatin.
2. Chromatin consists of DNA and the
proteins it is wrapped around.
3. The cells of every organism have a specific
number of chromosomes
1. Ex. humans have 46 chromosomes
5.2
Mitosis and Cytokinesis
TEKS 5A
Chromosomes condense at the start of mitosis.
• DNA wraps around proteins (histones) that condense it.
DNA double
helix
DNA and
histones
Chromatin
Supercoiled
DNA
5.2
Mitosis and Cytokinesis
TEKS 5A
• DNA plus proteins is called chromatin.
chromatid
• One half of a duplicated
chromosome is a chromatid.
• Sister chromatids are held
together at the centromere.
• Telomeres protect DNA and do
not include genes.
telomere
centromere
telomere
Condensed, duplicated chromosome
At the ends of each chromatid is an area
called the telomere.
-
The telomere is filled with non-coding DNA
Like a protective cap
Gets shorter during each cell division
Shortening is believed to be linked to aging
Telomeres
Chromatin v. chromosomes
4. Chromosomes are only visible during cell
division, when they are condensed. The rest
of the time the chromatin is spread
throughout the nucleus.
5. Before cell division, each chromosome is
replicated (meaning copied)
a) When a chromosome is replicated, it consists of
two identical “sister” chromatids.
b) When a cell divides the chromatids separate,
and one goes to each of the two new cells.
c) Sister chromatids are attached to each other at
the spot called the centromere.
5.2
Mitosis and Cytokinesis
TEKS 5A
Mitosis and cytokinesis produce two genetically identical
daughter cells.
Parent cell
• Interphase prepares
the cell to divide.
• During interphase,
the DNA is
duplicated.
centrioles
spindle fibers
centrosome
nucleus with
DNA
The Cell Cycle
• When a cell is NOT dividing, it is said to be
in interphase.
• The series of events that a cell goes
through as it grows and divides is called
the cell cycle.
Events of the cell cycle
Interphase, when the cell is NOT dividing, has three
phases: G1, S, and G2.
1. G1 phase: period of activity in which cells do
most of their growing.
a.
b.
Cells increase in size
Cells synthesize (make) new proteins and organelles
2. S phase: DNA (chromosomes) is replicated
3. G2: organelles and molecules required for cell
division are produced
M phase is the phase of cell division.
This includes:
1. Mitosis, the division of the cell nucleus,
which is made up of four segments
including prophase, metaphase, anaphase,
and telophase.
2. Cytokinesis, or the division of cytoplasm.
G1 phase
M phase
S phase
G2 phase
5.2
Mitosis and Cytokinesis
• Mitosis divides the cell’s nucleus in four phases.
– During prophase, chromosomes condense and
spindle fibers form.
TEKS 5A
Mitosis
There are four phases in mitosis:
1. Prophase
a.
b.
Longest phase in mitosis (take 5060% of total time mitosis requires)
Chromosomes become visible
because they are condensed
c.
Centrioles become visible on opposite
sides of the nucleus
i.
ii.
iii.
d.
e.
The centrioles help organize the spindle, a
structure made of microtubules that helps
separate the chromosomes
Chromosomes attach to the spindle
fibers near the centromere
Plant cells to not have centrioles but do
have mitotic spindles
Nucleolus disappears
Nuclear envelope breaks down
5.2
Mitosis and Cytokinesis
• Mitosis divides the cell’s nucleus in four phases.
– During metaphase, chromosomes line up in the
middle of the cell.
TEKS 5A
2. Metaphase
a. Chromosomes line up in the center of
the cell
b. Microtubules connect to the
centromeres
5.2
Mitosis and Cytokinesis
• Mitosis divides the cell’s nucleus in four phases.
– During anaphase, sister chromatids separate to
opposite sides of the cell.
TEKS 5A
3. Anaphase
a.
Centomeres split and the sister
chromatids separate and become
individual chromosomes
b.
Chromosomes move and
separate into two groups
near the spindle
c.
Anaphase ends when the
chromosomes stop moving
5.2
Mitosis and Cytokinesis
• Mitosis divides the cell’s nucleus in four phases.
– During telophase, the new nuclei form and
chromosomes begin to uncoil.
TEKS 5A
4. Telophase
a. Chromosomes change form being condensed
to dispersed
b. A nuclear envelope forms around each cluster
of chromosomes
c. Spindle breaks apart
d. Nucleolus is visible in each daughter nucleus
Telophase in the
midbodies of two
daughter cells
5.2
Mitosis and Cytokinesis
• Cytokinesis differs in animal and plant cells.
– In animal cells, the
membrane pinches
closed.
– In plant cells, a cell
plate forms.
TEKS 5A
Cytokinesis
• Mitosis occurs within the cytoplasm of one cell.
• Cell division is complete when the cytoplasm
divides.
• In plants, a structure called the cell plate forms
between the two daughter nuclei. The cell plate
develops into a cell membrane and cell wall.
Cytokinesis
• In animal cells, the cell membrane is
drawn inward until the cytoplasm is
pinched into two equal parts. Each part
has a nucleus and cytoplasmic organelles.
The cleavage of
daughter cells is
almost complete; this
is visualized by
microtubule staining
Spindle
forming
Centrioles
Nuclear
envelope
Chromatin
Centromere
Centriole
Chromosomes (paired
chromatids)
Interphase
Prophase
Cytokinesis
Centriole
Telophase
Nuclear envelope
reforming
Spindle
Individual chromosomes
Anaphase
Metaphase
5.3
Regulation of the Cell Cycle
TEKS 5A, 5B, 5C, 5D, 9C
The student is expected to:
5A describe the stages of
the cell cycle, including
deoxyribonucleic acid (DNA)
replication and mitosis, and the
importance of the cell cycle to the
growth of organisms;
5B examine specialized cells,
including roots, stems, and leaves of
plants; and animal cells such as
blood, muscle, and epithelium;
5.3
Regulation of the Cell Cycle
TEKS 5A, 5B, 5C, 5D, 9C
(Continued)
5C describe the roles of DNA,
ribonucleic acid (RNA), and
environmental factors in cell
differentiation;
5D recognize that disruptions of
the cell cycle lead to diseases
such as cancer;
9C identify and investigate the role of
enzymes
5.3
Regulation of the Cell Cycle
TEKS 5A, 5B, 5C, 5D, 9C
KEY CONCEPT
Cell cycle regulation is necessary for healthy
growth.
Regulating the Cell Cycle
Different cell types divide at different rates.
Examples:
– Muscle cells and nerve cells do not divide once
they have developed.
– Skin cells and cells in the bone marrow that
make blood cells divide rapidly.
Regulating Cell Divisions
• Internal regulators – Signals from within
the cell to regulate the cell cycle.
– They make sure everything is complete
before moving on.
Regulating Cell Divisions
• External regulators – Stimulate or
suppress cell growth by recognizing the
surrounding situation.
– Injury repair
– Embryonic stem cell differentiation
5.3
Regulation of the Cell Cycle
TEKS 5A, 5B, 5C, 5D, 9C
Internal and external factors regulate cell division.
• External factors include physical and chemical signals.
• Growth factors are proteins that stimulate cell division.
– Most mammal cells form a single layer in a culture
dish and stop dividing once they touch other cells.
5.3
Regulation of the Cell Cycle
TEKS 5A, 5B, 5C, 5D, 9C
• Two of the most important internal factors are kinases
and cyclins.
• External factors trigger internal factors, which affect the
cell cycle.
Proteins called Cyclins are present when
the cell is dividing and are absent when
the cell is not dividing.
They regulate the timing of the cell cycle
Controls on cell division
• Cell growth and cell division can be turned
on and off.
• When you are injured your cells divide
rapidly to repair the injury. When the
injury has healed, the cells stop dividing.
5.3
Regulation of the Cell Cycle
TEKS 5A, 5B, 5C, 5D, 9C
• Apoptosis is programmed cell death.
– a normal feature of healthy organisms
– caused by a cell’s production of self-destructive
enzymes
– occurs in
webbed fingers
development
of infants
Uncontrolled cell growth
1.
2.
3.
4.
When cells in your body CANNOT control cell
growth and division, cancer may form.
Cancer cells cannot respond to the signals that
regulate the division of cells.
When cancer cells have been dividing
uncontrollably, tumors form.
Tumors can damage surrounding tissue.
Cells from tumors can break free and travel to
other parts of the body, forming new tumors.
5.3
Regulation of the Cell Cycle
TEKS 5A, 5B, 5C, 5D, 9C
Cell division is uncontrolled in cancer.
• Cancer cells form disorganized clumps called tumors.
– Benign tumors remain clustered and can be removed.
– Malignant tumors metastasize, or break away, and can
form more tumors.
normal cell
cancer cell
bloodstream
Cancer
• Cancer cells tend to have a damaged
oncogene.
– This gene possess the information needed to
respond to internal and external regulators.
During the Reading
Define the following
1. Metastasis :
2. Benign:
The process or condition of
abnormal cell migration and tissue
invasion.
Cells that stay where they are usually
considered as a Tumor. (Not Cancer)
3. Malignant:
Cells can break off and infect other areas
of the body (Cancer)
There are several reasons that cells may lose
the ability to control growth.
Examples:
1. smoking
2. radiation exposure
3. viral infection
Scientists who study cancer are researching
how cells divide.
5.3
Regulation of the Cell Cycle
TEKS 5A, 5B, 5C, 5D, 9C
• Cancer cells do not carry out necessary functions.
• Cancer cells come from normal cells with damage to
genes involved in cell-cycle regulation.
5.3
Regulation of the Cell Cycle
TEKS 5A, 5B, 5C, 5D, 9C
• Carcinogens are substances known to promote cancer.
• Standard cancer treatments typically kill both cancerous
and healthy cells.
Reviewing Mitosis
When does the following occur?
(Name the phase of the cell cycle. If it is in mitosis,
name the phase of mitosis)
1. Sister chromatids separate.
Mitosis - Anaphase
2. Chromosomes line up across the center of the cell.
Mitosis - Metaphase
3. The cell’s DNA molecules are copied. S Phase
4. The cytoplasm pinches in half. Cytokinesis
5. A spindle forms.
Mitosis - Prophase
What are the
structures shown?
A. Sister chromatids
B. Centromere
How many copies of
the cell’s DNA are
shown here?
2
Cell Cycle
Interphase
? Phase
Mitosis
M Phase
Cytokinesis
?
Prophase
?
?
Metaphase Anaphase
?
Telophase
A
B
What is the name of the
structure labeled:
Centriole
A? __________________
Chromosome
B? __________________
C
Spindle fiber
C? __________________
If your were to examine a sample of 1000 cells undergoing
mitosis, in which of the phases listed below would you expect
to find most of the cells?
A. Prophase
B. Metaphase
C. Anaphase
D. Telophase