Transcript Cell Growth and Division

Cell Growth and Division
Cell Size
8
micrometers in diameter to 1 meter
with small diameters.
 Most cells are between 2 and 200
micrometers in diameter.
 Human Body:
– Smallest: sperm cells
– Largest: ovum
– Longest: nerve cells
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Largest Living Cell- Ostrich Egg (unfertilized)
Comparison of Cell sizes
Cell Size Limitations
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Cell must be small
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Rate of Diffusion
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DNA (molecule where critical information
stored) Too large “Information Crisis”
– Large need more food
– Must export waste
– Size :diffusion slower and less efficient.
– Cell cannot survive unless
• enough DNA to support protein needs
• cell activities are carried out quickly and efficiently
Cell Size Increase
Not enough cell membrane to adequately supply the cell
interior with enough oxygen, water, and food.
Result: Cell Death
Surface area-to-volume ratio
As cell’s size increases, its
volume increases much faster
than its surface area.
Surface Area and Volume
Surface Area: 6 (# of sides) x A x A
Volume: A x A X A
•Cube doubled
•Outside Grows by 4 x
•Inside grows by 8 x
Cell Growth and Reproduction
Asexual Versus Sexual
Reproduction
Asexual
 Genetically identical
offspring
 Single Cell
– ex. Bacteria
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Multi Cellular- Break off
and new organism
produced
– ex. Hydra
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Sexual
Offspring inherit genetic
information from each
parent.
Most plants and animals,
some single celled
organisms.
Asexual Versus Sexual
Reproduction
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Asexual
Survival Strategy
Better the conditions the
faster reproduce, better
chance of survival,
As long as conditions
favorable; genetically
identical has advantages
Lack of diversity a
disadvantage when
conditions change and
are not favorable.
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Sexual
Different survival strategy
Finding a mate, growth
and development take
more time.
Genetic diversity; better
tolerate change
Both Sexual and Asexual
Ex. Yeast
 Mostly asexual, however, may under certain
conditions reproduce sexually.
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Cell Theory
All cells come from pre-existing
cells!
Cell division results in two cells
that are identical to the original
parent cell.
Prokaryotic Cells
Lack nucleus & many organelles
 DNA molecule found in cytoplasm
 Most contain single, circular DNA with all
genetic information

Chromosomes
Chroma (Greek) “colored”
Soma “body”
Genetic information is bundled into
packages of DNA
Structure of the Eukaryotic
Chromosome
Exist as CHROMATIN—Long strands of
DNA wrapped around proteins.
 Microscope—Plate of spaghetti

Components
• Sugar-Deoxy-ribose –
derived from ribose sugarone less oxygen
• Phosphate Group backbone
• 4 Nitrogen Bases-In
complementary base pairs
held by hydrogen bonds
• Adenine & Thymine
• Cytosine &Guanine
CHROMOSOMES
Make it possible to separate DNA
precisely during cell division
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A series of events the cells go through
as they grow and divide
During cell cycle, a cell grows, prepares
for division, and divides to form two
daughter cells.
CELL CYCLE
Prokaryotic Cell Cycle

Regular pattern of
growth, DNA
replication, and cell
division that can take
place under ideal
conditions
 Just beginning to
understand process
 Form of reproduction
called Binary Fission.
 Result-two genetically
identical cells.
Cell Cycle
– Interphase-Period of cell cycle b/w cell
division
• most of the cell’s metabolic functions are
carried out
• chromosomes are replicated
• LONGEST of Cell Cycle
– Cell Division (M Phase)
• Mitosis when nuclear division occurs, leading
to the formation of two daughter cells.
• The division of the cytoplasm, called
cytokinesis, follows mitosis.
• Length of cell cycle depend on the type of cell
Eukaryotic Cell Cycle
Interphase: Cell prepares for
Mitosis
Cell grows in size
 Carry on metabolism
 Chromosomes are duplicated for cell
division.
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Interphase
G1 Phase: Cell Growth
• Most cell growth
• Increase in size
• Synthesize new proteins and
organelles
Interphase Continued
S Phase
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“S” Synthesis
DNA is synthesized when
chromosomes replicated.
Result: Cell has 2x as
much DNA
G2 Phase: Preparing for
Cell Division
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Shortest phase of
Interphase
Organelles and
molecules required for
cell division are
produced.
Result: Cell ready for
division
Helicase-(Enzyme) unzips/breaks
hydrogen bonds b/w base pairs
Nitrogen Bases
M Phase
Produces 2 daughter cells
 “M” comes from Mitosis
 Cell division relatively quick
 Includes Mitosis and Cytokinesis
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– Mitosis-division of the cell nucleus
• 2 daughter cells produced with genetic information
– Cytokinesis-division of the cytoplasm
Mitosis: A period of nuclear
division
Mitosis
Prophase
 Metaphase
 Anaphase
 Telophase
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Prophase
1st / longest phase of mitosis.
 Chromatin coils up (condenses)chromosomes.
 Duplicate chromosomes become visible
 Two halves of the double structure are called
sister chromatids. (Exact Copies of each
other)
 Centromere—holds together sister
chromatids.
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Prophase continued…
Nucleus disappears
 Nuclear envelope and nucleolus disintegrate.
 Animals—centrioles migrate to opposite end
of the cell.
 Centriole—Small, dark, cylindrical structures
that are made of microtubules and are
located just outside the nucleus.(animal cells
only)
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Prophase continued…
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Spindle—A football shaped, cage-like
structure consisting of thin fibers made of
microtubules.
Metaphase: Second stage of
mitosis
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Chromosomes
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One sister chromatid’s spindle fiber extends to one
pole, and the other extends to the opposite poles
(ensures a complete set of chromosomes)
– Line up at center of cell
– Attach to the spindle fibers via centromeres.
– Pulled by spindle fibers and line up on the midline
(equator).
Anaphase: Third Phase of Mitosis
 Separation
of sister chromosomes
– Centromeres split apart and chromatid pair
separate
– Pulled apart by the shortening of the
microtubules in the spindle fiber.
Telophase: 4th phase of mitosis
Chromosomes reach opposite poles of cell.
 Prophase changes are reversed
(independent existence).
 Chromosomes unwind; Spindle breaks down;
nucleolus reappears; new nuclear envelope
forms each set of chromosomes; new double
membrane begins to form.
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Cytokinesis
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Cytoplasm division
Animal Cells—Membrane is drawn inward until the
cytoplasm is pinched into two nearly equal parts.
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Plant Cells—(cell membrane not flexible enough to
draw inward because of rigid cell wall) Cell plate
forms b/w the divided nuclei. Gradually, cell plate
develops into cell membrane that separates two
daughter cells.
Result of Mitosis

Two new cells with chromosome
sets identical to those of the
parents; Carry out same function of
parent cells; Grow and divide like
parent cells.
 Tissues: group of cells that work
together to do a specific function.
 Organs: group of two or more
tissues organized to perform
complex activities within an
organism.
 Organ Systems: Multiple organs
that work together to perform
specific life function.
Cell Cycle
Purpose of Cell Division and
Mitosis
Keep total cell number in a mature organism
relatively constant,
 Replace worn-out or damaged cells,
 Enable a multicellular organism to grow to
adult size.
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Control of Cell Cycle
Cell cycle
 24 to 48 hours
 less then an hour
 never divide only mature
Most muscle and nerve never
divide
A mistake in the cell cycle can
lead to cancer.
Cell Regulation
Injury occurs-cells divide rapidly, healing
process begins, as near completion, slows
down, everything returns to normal
 Cyclin-a protein that regulates timing of cell
cycle
 Regulatory Proteins-Proteins that control cell
cycle (both inside and outside cell)
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– Functions: slow down or stop cell division, start
cell division, etc
– Internal Regulators- allow cell to proceed only
when certain events have occurred
– External Regulators-Respond to events outside
cell.
• Growth factors-stimulate growth and division of cells.
Control of the Cell Cycle
 Enzymes
– Begin and drive the cell cycle
– Control the cycle through its phases.
 Cell can lose control (uncontrolled
dividing)
– failure to produce certain enzymes
– production of other enzymes at the wrong time.
 Cancer
is the result of uncontrolled cell
division.
Cell Death
 Death
due to injury
 Apoptosis-Cell may be programmed to
die (self-destruction)
– Controlled steps to death
• Cell and its chromosomes shrink
• Parts of cell membrane break off
• Neighboring cells clean up cell’s remains
Causes of loss of control of cell
cycle
Environmental Factors
 Changes in enzyme production
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– Enzyme production is directed by genes located
on the chromosome.
– A gene is a segment of DNA that controls the
production of a protein.
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Many studies point to portion of interphase
just before DNA replication as being a key
control period.
Cancer: A mistake in the
Cell Cycle
Expressed as cancer when
something prompts the damaged
genes into action.
Cancer
Cancerous cells form masses of tissue called
tumors that deprive normal cells of nutrients.
 Late Stages: Cancer cells enter the
circulatory system and spread throughout the
body (Metastasis), forming new tumors that
disrupt the function of organs, organ
systems, and ultimately the organism.
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In Cancer Cells
•There is no awareness of surroundings.
•Cells do not stop dividing when crowded.
•Cells do not stop after a set number of divisions.
•Cells do not enter a resting state.
•Cells divide faster and take less time to complete
the cycle.
Cancer: 2nd Leading Cause of
death in the United States
(heart disease #1)
Environmental and Genetic Factors
 Cigarette smoke
 Air
 Water pollution
 Exposure to UV Radiation
 Viral Infections
 Instogram, Facebook and Twitter
 p53 (gene halts cell cycle)
Treatments
Surgery (tumor removal)
 Chemotherapy-Chemical compounds that kill
cancer cells and/or slow growth
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– Interfere with healthy cells
– Serious side effects
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Radiation
Cancer Prevention
Link between healthy lifestyle and the
incidence of cancer.
 Diets low in fat and high in fiber.
 Minimal amounts of fat.
 Vitamins and minerals; carotenoids, vitamins
A, C, and E and calcium.
 Daily exercise
 No smoking
 Don’t use Instogram,
Face Book and Twitter
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Cell Differentiation
Human body-estimated one hundred trillion
cells.
 Embryo-developmental stage of a
multicellular organism; organism's cells
become more and more differentiated and
specialized for specific function.
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Differentiation
During development of an
organism, cells differentiate into
many types of cells
9959 cell with precisely determined functions
Stem Cells and Development
Totipotent-cells that are able to develop into
any type of cell found in the body.
 Blastocyst- after about 4th day of
development human embryo forms; a
hollow ball of cells with a cluster of cells
inside (inner cell mass); differentiation occurs
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– Outer cells form tissue that will attach to mom
– Inner cells mass becomes the embryo
Pluripotent Cells
Cells that can develop into MOST,
but not all, of body’s cell types.
Ex. Inner cell mass (can not form
tissues surrounding embryo
Stem Cells
Unspecialized cells from which
differentiated cells develop
Stem Cells
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Embryonic Stem Cells-found in early
embryos
– 1998 researchers from way to grow in culture
– Can make different types of cells; sperm made
from embryonic stem cells were used to
generate live mice.
Adult Stem Cells
Cells that differentiate to renew and replace
cells in the adult body-limited potential
 Multipotent-cells that can develop into many
types of differentiated cells.
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– Most only produce type of cells of given organ or
tissue
• Eg-adult stem cells in bone marrow can develop into
several types of blood cells; while brain stem cells can
produce neurons (nerve cells)
Frontiers in Stem Cell
Important to human health
 Use of undifferentiated cells to repair or
replace badly damaged cells and tissues.
 Ethical Issues
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– Embryonic stem cells (from early embryos)
• Embryo‘s entitled to rights and protections of human
beings.
• Government funding-political issue
• Ethical issue of life and death
– Technology solutions becoming available