Download Cellular Respiration Chapter 9

Chapter 8
Cell Growth and Division
Limits to Cell Growth
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What problems does growth cause for cells?
The larger a cell becomes, the more demands
a cell places on its DNA and the harder it is
for the cell to move enough nutrients and
wastes across the cell membrane.
Think of a library. If the amount of books
doesn’t change and the town continues to
grow, will the library be able to meet the
needs of the community?
Limits to Cell Growth
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The rate at which food, oxygen, water, and
wastes are moved in and out of the cell is
dependent on the surface area of the cell.
The rate at which food, oxygen, and water are
used and waste is produced depends on the
cell’s volume.
Limits to Cell Growth
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Ratio of Surface Area to Volume
- As the length of a cell increases, its volume
increases faster than the surface area.
- The decrease in the cell’s ratio of surface
area to volume makes it more difficult for the
cell to move needed materials in and waste
products out quickly enough for the cell to
survive.
Limits to Cell Growth
Division of the Cell
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Before it becomes too large, a growing cell
divides forming two “daughter” cells.
The process by which a cell divides into two
new daughter cells is called cell division.
8–1 Review
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As a cell increases in size, which of the
following increases most rapidly?
• surface area
• volume
8–1 Review
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If an imaginary cube-shaped cell has a length
of 6 cm, its ratio of surface area to volume is
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1 : 1.
6 : 1.
36 : 1.
1 : 6.
8–1 Review
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The process by which a cell divides into two
new daughter cells is called
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cell growth.
cell division.
DNA replication.
cell multiplication.
8–1 Review
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When one cell divides in two, what happens to the
surface area to volume ratios in the new cells?
• There is no change in the amount of material
exchanged.
• Each new cell can exchange more material than the
original cell.
• Each new cell can exchange less material than the
original cell.
• The two new cells cannot be compared to the original
cell.
8–1 Review
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When a growing cell undergoes cell division,
each new cell gets
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half the DNA from the original cell.
twice as much DNA as the original cell.
a random sample of the DNA in the original cell.
a full copy of all the DNA in the original cell.
Chromosomes
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Eukaryotic cells: during cell division, DNA is
coiled tightly into compact structures called
chromosomes.
- Rod-shaped structures made of DNA and
protein.
Chromosomes (cont’d)
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Between cell divisions, DNA is not so tightly
coiled into chromosomes and is called
chromatin.
Chromosomes (cont’d)
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Each chromosome
consists of two identical
“sister” chromatids.
Each pair of chromatids
is attached at an area
called the centromere.
When the cell divides,
the chromatids
separate.
Each new cell gets one
chromatid.
Sister chromatids
Centromere
Chromosome Number
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Each species has a characteristic
chromosome number
Human beings have 46 chromosomes.
Dogs have 78 chromosomes.
The number of chromosomes does NOT
determine the complexity of the organism.
Human Karyotype
Chromosome Number (cont’d)
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Chromosomes are characterized as 2 types:
- Sex chromosomes – determines the sex of
an organism; may carry genes for other
characteristics.
- Autosomes – represent all of the other
chromosomes.
Sex Chromosomes
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Humans have 2 sex
chromosomes: X or Y.
Normal females have
XX and males have
XY.
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Autosomes
•
All other
chromosomes
• Humans have 2 sex
chromosomes and
44 autosomes.
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Homologous Chromosomes
•
Every cell produced by sexual reproduction has 2
copies of each autosome.
- One from each parent.
• The 2 copies are homologous chromosomes or
homologues.
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Homologous Chromosomes
(cont’d)
Same size and
shape and carry
genes for the same
traits.
• Humans have 22
homologous pairs
and 2 sex
chromosomes.
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Diploid
•
Represented by 2n.
• Cells with 2 sets of chromosomes, with both
chromosomes for each homologous pair.
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Diploid (cont’d)
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Cells also have 2 sex chromosomes.
• All normal human cells, except reproductive cells
(sperm cells and egg cells), are diploid.
• Humans have a diploid number of 46.
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Haploid
•
Represented by 1n or n.
• Human sperm and egg cells have only one set
of chromosomes, which is half the number in a
diploid.
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Haploid (cont’d)
•
Haploid cells contain only one chromosome of
each homologous pair and only one sex
chromosome.
• When a sperm (1n) and an egg (1n) combine,
they form a cell which is diploid (2n).
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Cell Division: Prokaryotes
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Divide by binary fission division into 2 offspring.
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Cell Division: Prokaryotes
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3 stages:
1.
Chromosome copies
itself.
2.
Cell grows to twice the
original size.
3.
Cell wall forms between
the 2 chromosomes and
cell splits into 2 new
cells, identical to the
original.
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Cell Division
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In eukaryotes, cell division occurs in two
major stages.
The first stage, division of the cell nucleus, is
called mitosis.
The second stage, division of the cell
cytoplasm, is called cytokinesis.
Reproduction by mitosis is considered
asexual, since the cells produced by mitosis
are genetically identical to the parent cell.
The Cell Cycle
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The cell cycle is the series of events that
cells go through as they grow and divide.
During the cell cycle, a cell grows, prepares
for division, and divides to form two daughter
cells, each of which then begins to cycle
again.
Interphase is the period of growth that occurs
between cell divisions.
The Cell Cycle
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The cell cycle consists of four phases:
• G1 (First Gap Phase)
• S Phase
• G2 (Second Gap Phase)
• M Phase
Events of the Cell Cycle
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Events of the Cell Cycle
• During the normal cell cycle, interphase can be
quite long, but the process of cell division takes
place quickly.
• Interphase is divided into three phases: G1, S, and
G 2.
• During G1, the cell,
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increases in size (this is where cells do most of their
growing)
synthesizes new proteins and organelles
Events of the Cell Cycle
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During the S phase,
• chromosomes are replicated
• DNA synthesis takes place
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Once a cell enters the S phase, it usually
completes the rest of the cell cycle.
Events of the Cell Cycle
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The G2 Phase (Second Gap Phase)
• When the DNA replication is completed, the cell
enters the G2 phase – the shortest of the three
phases of interphase!
• Organelles and molecules required for cell division
are produced during this phase.
• Once G2 is complete, the cell is ready to start the
M phase—Mitosis.
Events of the Cell Cycle
Cell Cycle
Mitosis
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Biologists divide the events of mitosis
into four phases:
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Prophase
Metaphase
Anaphase
Telophase
Section 10-2
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Prophase
Mitosis
Prophase
Spindle
forming
Chromosomes
(paired
chromatids)
Centromere
Mitosis
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Prophase
• Prophase is the first
and longest phase of
mitosis.
• The centrioles
separate and take up
positions on opposite
sides of the nucleus.
Centriole
Spindle
forming
Centromere
Chromosomes
(paired
chromatids)
Mitosis
• The centrioles lie in a
region called the
centrosome.
• The centrosome
helps to organize the
spindle, a fanlike
microtubule structure
that helps separate
the chromosomes.
Centriole
Spindle
forming
Centromere
Chromosomes
(paired
chromatids)
Mitosis
• Chromatin
condenses into
chromosomes.
• The centrioles
separate and a
spindle begins to
form.
• The nuclear
envelope breaks
down.
Centriole
Spindle
forming
Centromere
Chromosomes
(paired
chromatids)
Mitosis
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Metaphase
Centriole
Spindle
Centriole
Metaphase
Mitosis
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Centriole
Metaphase
• The second phase of
mitosis is metaphase.
• The chromosomes
line up across the
center of the cell.
• Microtubules connect
the centromere of
each chromosome to
the poles of the
spindle.
Spindle
Mitosis
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Anaphase
Individual
chromosomes
Anaphase
Mitosis
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Anaphase
Individual
chromosomes
• Anaphase is the third
phase of mitosis.
• The sister chromatids
separate into
individual
chromosomes.
• The chromosomes
continue to move until
they have separated
into two groups.
Mitosis
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Telophase
Nuclear
envelope
reforming
Telophase
Mitosis
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Telophase
• Telophase is the
fourth and final
phase of mitosis.
• Chromosomes
gather at opposite
ends of the cell
and lose their
distinct shape.
• A new nuclear
envelope forms
around each
cluster of
chromosomes.
Cytokinesis
 Cytokinesis
Cytokinesis
Cytokinesis
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During cytokinesis,
the cytoplasm
pinches in half.
The area of the cell
membrane that
pinches in half is the
cleavage furrow.
Each daughter cell
has an identical set
of duplicate
chromosomes.
Cytokinesis: Animals
Cytokinesis
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In plants, a structure known as the cell plate
forms midway between the divided nuclei.
Cell plate
Cell wall
Cytokinesis
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The cell plate gradually develops into a
separating membrane.
A cell wall then begins to appear in the cell
plate.
8-2
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The series of events that cells go through as
they grow and divide is called
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the cell cycle.
mitosis.
interphase.
cytokinesis.
8-2
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The phase of mitosis during which the
chromosomes line up across the center of the
cell is
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prophase.
metaphase.
anaphase.
telophase.
8-2
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Cytokinesis usually occurs
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at the same time as telophase.
after telophase.
during interphase.
during anaphase.
8-2
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DNA replication takes place during the
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S phase of the cell cycle.
G1 phase of the cell cycle.
G2 phase of the cell cycle.
M phase of the cell cycle.
8-2
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During mitosis, “sister” chromatids separate
from one another during
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telophase.
interphase.
anaphase.
metaphase.
Regulating the Cell Cycle
Controls on Cell Division
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Controls on Cell Division
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Experiments show that normal cells will
reproduce until they come into contact with other
cells.
When cells come into contact with other cells,
they respond by not growing.
This demonstrates that controls on cell growth
and division can be turned on and off.
What happens when you sustain an injury like a
cut or a break?
Controls on Cell Division
• Contact Inhibition
Cell Cycle Regulators
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Cell Cycle Regulators
• The cell cycle is regulated by a specific protein.
• The amount of this protein in the cell rises and falls in
time with the cell cycle.
• Scientists called this protein cyclin because it
seemed to regulate the cell cycle.
• Cyclins regulate the timing of the cell cycle in
eukaryotic cells.
• More recently, dozens of other proteins have been
discovered that help to regulate the cell cycle.
Cell Cycle Regulators
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Internal Regulators
• Proteins that respond to events inside the cell are
called internal regulators.
• Internal regulators allow the cell cycle to proceed
only when certain processes have happened
inside the cell.
• Ex) several regulatory proteins make sure a cell
does not enter mitosis until all its chromosomes
have been replicated.
Cell Cycle Regulators
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External Regulators
• Proteins that respond to events outside the cell are
called external regulators.
• External regulators direct cells to speed up or slow
down the cell cycle.
• Growth factors are among the most important
external regulators – they stimulate the growth and
division of cells (especially important during
embryonic development and wound healing).
• Keep body tissues from disrupting one another by
preventing excessive cell growth.
Uncontrolled Cell Growth
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Uncontrolled Cell Growth
• Cancer is a disorder in which some of the
body's own cells lose the ability to control
growth.
• How are cancer cells different from other cells?
Uncontrolled Cell Growth
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Cancer cells do not respond to the signals that
regulate the growth of most cells.
Cancer cells divide uncontrollably and form masses of
cells called tumors that can damage the surrounding
tissues.
Cancer cells may break loose from tumors and spread
throughout the body, disrupting normal activities and
causing serious medical problems or even death.
Caused by smoking tobacco, radiation exposure, and
even viral infection.
Many cancer cells have a defect in gene p53, which
normally halts the cell cycle until all chromosomes
have been replicated.
Tumors
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Tumor a piling up of cells due to
uncontrolled cell division
“Mitosis gone wild”
Tumors
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Types of tumors:
(1) Benign
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Non-cancerous
Usually don’t spread
Usually no threat
Usually removed by
surgery (if needed)
• Ex. Cysts, warts
Tumors
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(2) Malignant
• Cancerous
• If a person
develops a
malignant tumor,
that person is said
to have cancer
(diagnosed w/
cancer)
• Invades and
destroys healthy
tissues of the body
• Metastasize (cells
spread beyond
their original site)
Biopsy
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A procedure done to check for cancerous
cells
Stem Cells
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A cell whose job is not
yet determined
All other cells in the body
“stem” from these cells
They wait in the body
until they get a signal to
DIFFERENTIATE
(gradually change into
the desired cell type)
They can become skin
cells, RBC’s, nerve cells,
skeletal muscle cells
What are stem cells & why are they
important?
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Undifferentiated cells that
renew themselves over long
periods through cell division
Under certain conditions, these
cells will differentiate and
become functioning body cells
such as muscle or neurons
A 3-5 day embryo (blastocyst)
has a group of 30 or more cells
that will become all the cells of
the body (all cells stem from
these)
Scientists hope to use these
cells to treat diseases