Transcript Cell Growth and Division

Biology Chapter 10:
Cell Growth and Division
*This presentation contains copyrighted material.
THINK ABOUT IT –
Limits to Cell Size
1. When a living thing grows, what happens
to its cells?
2. What is there about growth that requires
cells to divide and reproduce themselves?
What are some of the difficulties a cell faces
as it increases in size?
The larger a cell becomes, the more demands
the cell places on its DNA. In addition, a
larger cell is less efficient in moving
nutrients and waste materials across its
cell membrane.
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Information “Overload”
– Living cells store critical information in
DNA.
– As a cell grows, that information is used to
build the molecules needed for cell growth.
– As size increases, the demands on that
information grow as well. If a cell were to
grow without limit, an “information crisis”
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would
occur.
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Information “Overload”
–
Compare a cell to a
growing town. The town
library has a limited
number of books. As the
town grows, these
limited number of books
are in greater demand,
which limits access.
–
A growing cell makes
greater demands on its
genetic “library.” If the
cell gets too big, the
DNA would not be able
to serve the needs of
the growing cell.
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Exchanging Materials
– Food, oxygen, and water enter a cell through the
cell membrane. Waste products leave in the same
way.
– The rate at which this exchange takes place
depends on the surface area of a cell.
– The rate at which food and oxygen are used up
and waste products are produced depends on the
cell’s volume.
– The ratio of Chap
surface
areaandtoDivision
volume is key to
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understanding why cells
Ratio of Surface Area to
Volume
– Imagine a cell shaped like a cube. As the
length of the sides of a cube increases, its
volume increases faster than its surface
area, decreasing the ratio of surface area
to volume.
– If a cell gets too large, the surface area of
the cell is not large enough to get enough
oxygen and nutrients in and waste out.
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Traffic Problems
–
To use the town analogy
again, as the town grows,
more and more traffic clogs
the main street. It becomes
difficult to get information
across town and goods in
and out.
–
Similarly, a cell that
continues to grow would
experience “traffic”
problems. If the cell got too
large, it would be more
difficult to get oxygen and
nutrients in and waste out.
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Division of the Cell
– Before a cell grows too large, it divides into
two new “daughter” cells in a process called
cell division.
– Before cell division, the cell copies all of its
DNA.
– It then divides into two “daughter” cells. Each
daughter cell receives a complete set of DNA.
– Cell division reduces cell volume. It also
results in an increased ratio of surface area to
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volume,
for
each
daughter
cell.
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Cell Division and Reproduction
How do asexual and sexual reproduction
compare?
– The production of genetically identical offspring
from a single parent is known as asexual
reproduction.
– Offspring produced by sexual reproduction
inherit some of their genetic information from
each parent.
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Asexual Reproduction
– In multicellular organisms, cell division
leads to growth. It also enables an
organism to repair and maintain its body.
– In single-celled organisms, cell division is
a form of reproduction.
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Asexual Reproduction
– Asexual reproduction is reproduction that
involves a single parent producing an offspring.
The offspring produced are, in most cases,
genetically identical to the single cell that
produced them.
– Asexual reproduction is a simple, efficient, and
effective way for an organism to produce a large
number of offspring.
– Both prokaryotic and eukaryotic single-celled
organisms and many multicellular organisms can
reproduce asexually.
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– -Bacteria cellsChap
reproduce
byDivision
binary fission
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Sexual Reproduction
- In sexual reproduction, offspring are
produced by the fusion of two sex cells –
one from each of two parents. These fuse
into a single cell before the offspring can
grow.
– The offspring produced inherit some
genetic information from both parents.
– Most animals and plants, and many
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single-celled
organisms,
reproduce
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sexually.
Cell Division -Eukaryotes
Two main types of division:
1. Mitosis- results in new cells with genetic
material that is identical to the genetic material
of original cell
During: growth, development, repair, asexual
reproduction (production of offspring from one
parent)
2. Meiosis- occurs during the formation of
gametes (reproductive cells, 1n), reduces the
chromosome number by ½ in new cells, often
combine to make 2n cells
Biology notes-Chapter
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Comparing Sexual and
Asexual Reproduction
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The Eukaryotic Cell Cycle
– The eukaryotic cell cycle
consists of four phases:
G1, S, G2, and M.
– Interphase is the time
between cell divisions. It
is a period of growth that
consists of the G1, S, and
G2 phases. The M phase
is the period of cell
division.
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Let's start from the beginning...
• A long time ago our
ancestors noticed
that some things
tended to reproduce
themselves - traits
were inherited.
Unfortunately, that's
not always a good
thing!
What is a chromosome?
• Threadlike structure in nucleus >
contains genetic information - passed on
from one generation of cells to the
next
– Genetic information = DNA (“blueprints”
of life)
– DNA in form of a code (genes) > dictates
everything from eye color to how long you
live
– “It’s in your genes” should actually be “It’s
in your DNA
Gene
• Sequence of DNA that codes for a
protein and determines a trait
– Trait = specific characteristic that varies from
one individual to another
– Ex: height, hair and eye color
• Genes are the bands on chromosomes.
– The thicker the band, the more information it
holds.
Living things grow by producing
cells.
bacteria (0.5 to 1.5 microns)
red blood cell (5 microns)
lymphocyte (5 to 8 microns)
As a cell grows larger, it…
• Places more demands on its DNA
– DNA “Overload”
– Compare to town library (town grows, more
demand for books)
• Has more trouble moving enough
nutrients and wastes across its membrane
(in and out of cell)
The cell will eventually divide into two
daughter cells.
Cell Division
• Process by which a cell
divides into two daughter
cells
– DNA replicated before division
– Each daughter cell gets one
complete set of genetic
information
• Two stages:
– Mitosis - nucleus divides to
form two identical nuclei
– Cytokinesis - cytoplasm divides
to form two identical cells
Chromosomes
• Made up of DNA (genetic information) and
proteins > chromatin
• Each chromosome has two identical “sister”
chromatids - one goes to each new cell
• Cells of every organism have specific
number of chromosomes
– Ex: fruit flies 8, carrots 18, humans 46
• Duplicated chromosomes are called dyads
• Duplicates held together by centromere
• Homologous pair = 1 of each pair
acquired from one of the parents
The Cell Cycle
• Cell grows, replicates its DNA, and
divides into two daughter cells
• Four phases
~ M phase > Mitosis and cytokinesis
(cell division)
~ S phase > Synthesis (chromosome
replication)
~ G1 and G2 > “Gap” phases (periods of
intense Growth and activity)
Interphase
• Period of cell cycle between cell
divisions
• All phases except M
– Made up of G1, S, and G2 phases
– Split because M phase occurs much more
quickly
• Includes: DNA replication, protein
synthesis, and synthesis of organelles
and materials needed for cell division
• Mitosis > Process in which the
nucleus divides to form two
identical nuclei
Four Phases of Mitosis
• Prophase
• Metaphase
• Anaphase
• Telophase
Prophase
• Chromatin condenses
into chromosomes
• Nucleolus disappears
• Centrioles separate
– Two tiny “anchors” in
cytoplasm near nuclear
envelope
• Fanlike fibers extend to
form spindle
Pair of
Centrioles
Chromosome
(two sister
chromatids)
Centromere
Metaphase
• Chromosomes line up along center of
cell
– Each chromosome connected to spindle
at centromere
(Imaginary line)
Anaphase
• Sister chromatids separate and
move to opposite sides of cell
Telophase
• Chromosomes gather at opposite
ends of cell
• Two new nuclear envelopes form
Chromosomes
gathering
New nuclear
envelopes
forming
Cytokinesis
• Cytoplasm pinches in half
• Each daughter cell has identical set of
duplicate chromosomes
Cytokinesis in Animal Cells
– The cell membrane is drawn in until the
cytoplasm is pinched into two equal parts.,
Cleavage furrow
– Each part contains its own nucleus and
organelles.
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Cytokinesis in Plant Cells
– In plants, the cell membrane is not flexible
enough to draw inward because of the rigid
cell wall.
– Instead, a cell plate forms between the
divided nuclei that develops into cell
membranes.
– A cell wall then forms in between the two
new membranes.
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Biology notes-Chapter
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New individual cell
10.1 Pre-Read Questions
1. Name 2 limitations to cell
growth.
2. How does DNA limit cell
growth?
3. Why is the ratio of surface area
to volume important?
4. Describe the process of cell
division.
Review: Cell Cycle
• Steps of Cell Division
– Mitosis
• Prophase
• Metaphase
• Anaphase
• Telophase /
Cytokinesis
Cyclin
• protein
• regulates the timing
of the cell cycle in
eukaryotic cells
Regulatory Proteins
• Two types
1.Internal
Regulators
2.External
Regulators
Internal Regulators
• proteins that respond to
events inside the cell
• signals cell cycle to
continue ONLY WHEN
OTHER THINGS ARE
COMPLETE
External Regulator
• proteins that respond to
events outside the cell
• direct cells to speed up or
slow down the cell cycle
• example: growth
regulators
Apoptosis
• Cells die in one of two ways, they either die
tragically from some unforeseen fashion, or
they die from Apoptosis. This is the regularly
scheduled death of a cell. Once it is
triggered, the cells and chromatin shrink, the
organelles are broken down and nearby cells
clean up the mess.
• Apoptosis is key for development of tissue
(you used to have a tail) and if it is triggered
incorrectly, leads to other problems (AIDS)
Uncontrolled Cell Growth
• Cancer
– body loses ability to control
growth
– does not respond to the
regulator proteins
– result = large masses of
cells
Tumors
• masses of cells
• damages the surrounding
tissues
• cells break off and
spread throughout the
body
Cause of cancer
• brought on by smoking
tobacco
• radiation exposure
• viral infection
• etc
10.3 Review Questions
1. Why is it important for cells to
have regulated cell growth?
2. What is the purpose of the
protein cyclin?
3. Compare and contrast internal
regulators and external
regulators.
4. What is cancer? What causes
cancer?
Uncontrolled Cell Growth
• Cancer
– Disorder in which some
cells lose ability to control
growth
– Cells do not respond to
signals that regulate
growth of most cells
– Result > divide
uncontrollably and form
masses of cells called
tumors
Results of Mitosis
• Mitosis is the division of a NUCLEUS
• Mitosis produces two new nuclei with the
SAME number of chromosomes as
original nucleus
• Mitosis is ASEXUAL
– ONE parent = 2 IDENTICAL daughters
The Stages of the Cell Cycle
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