Chapter 8:
Cellular
Respiration
Cellular Reproduction
“All cells come from cells”
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Life in humans begins a a single
cell
Asexual reproduction takes place
when a single-celled organism splits
into two individuals without the
participation of a sperm and egg
Sexual reproduction concerns the
union of a sperm and egg to make a
zygote
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Confers genetic variations
Cellular reproduction involves 2
processes: growth and cell division
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A cell duplicates its contents
(organelles, DNA) during growth
During cell division, cellular
contents and DNA of the parent
cell are distributed to the daughter
cells
Chromatin to Chromosome
Chromatin consists of strands of
DNA that are organized around
histone proteins
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Chromatin is wound around a
core of 8 histones to make a
bead or nucleosome
Chromatin forms a zigzag that
is folded into loops
There are 2 meters of DNA in a
human cell
Q: What apparent problem can you
see from this fact?
DNA replication allows a cell to
copy its DNA and pass a full copy
to each daughter cell
DNA and associated proteins are
packaged into a set of
chromosomes and condensed
During cellular reproduction , the chromatin is
further condensed multiple times into large
loops that produce a greatly compacted
chromosome
A duplicated chromosome is composed of 2
identical halves called sister chromatids held
together by a centromere
The number of chromosomes is characteristic of
each species
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A human cell has 46 chromosomes
The Cell Cycle
The cell cycle is a repeated sequence
of events in eukaryotes that involves
cell growth and nuclear division
It consists of an interphase stage
(G1, S, G2) and a mitotic (M) phase
Interphase: most of the cell cycle is
spent here
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o
G1 phase: A cell will double its
organelles (esp. mitochondria and
ribosomes) and gathers material
for DNA replication
G0: Cell division is arrested and
the cell exist as in “post-mitotic” or
quiescent state
S phase: synthesis of DNA for
DNA replication
•
o
The chromosomes are replicated
G2 phase: The cell will synthesize
proteins, such as microtubules,
needed for cell division
Mitotic phase: cell division occurs during
the M stage
M stands for mitosis, a type of
nuclear division
The end result is that daughter nuclei
will be identical to the parent cell and
to each other
Cytokinesis occurs and the daughter
cells will have the same number and
kinds of chromosomes
The Basis of Mitosis
The duplicated nuclear contents of the
parent cell are distributed equally to
the daughter cells
Every cell in an organism has an even
number of chromosomes because the
parent cell contributed half of the
chromosomes to the new individual
A chromatid is a single DNA
double helix
The chromatid is duplicated to
make a sister chromatid with the
same sequence of base pairs
The sister chromatids are held
together by a centromere
Spindle fibers from the
centrosome pull the chromatids
apart during cell division
In the first stage of mitosis,
centrosomes separate and move
to opposite sides of the nucleus
and form poles of spindle fibers
There are 4 phases: prophase,
metaphase, anaphase, and telophase
Phases of Mitosis
Phases of mitosis
Cytokinesis in Animal and
Plant Cells
Cytokinesis is a division of the cytoplasm
that usually follows mitosis in most cells
but not all cells
In animal cells, a cleavage furrow or an
indention of the membrane is formed
between the two daughter nuclei at the
end of anaphase
The contractile ring, a band of actin
filaments, forms a circular
constriction between the two cells
until they are 2 independent
daughter cells
In plant cells, furrowing is not allowed
due to the rigid cell wall
Instead, a small, flattened disk
appears between the two daughter
plant cells
Vesicles produced by the Golgi fuse
to the disk forming a cell plate
The cell plate expands until it reaches
the plasma membrane and fuses with
it
Cell Cycle Checkpoints
G1 checkpoint: is the most significant
because the cell is committed to divide
once it passes this checkpoint
If the cell does not pass this
checkpoint,
1.
2.
3.
It could enter G0 where it
continues to perform its normal
functions but does not divide
Initiate DNA repair if DNA is
damaged
Death by apoptosis
(programmed death)
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G2 checkpoint: the cell verifies that
DNA has replicated and mitosis can
proceed
o
M checkpoint: pauses between
metaphase and anaphase to allow the
proper attachment of chromosomes to
spindle fibers
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This also ensures that the
chromosomes will be distributed
accurately to the daughter cells
Internal and External Signals
Internal and external signals controlled
the checkpoints of the cell cycle
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A signal can be stimulatory or
inhibitory
Telomere are repeating DNA base
sequence at the end of the
chromosomes that act like protective
caps against degradation of DNA
Kinases are enzymes that remove
phosphate from ATP and add it to
another molecule
Each time a cell divides, some portion
of a telomere is lost
S-kinase and S-cyclin
M-kinase and M-cyclin
The cell will die by apoptosis when the
telomeres become too short
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Growth factors stimulate cells to go
through the cell cycle, even those in G0
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EGF, hormones (estrogen)
Contact inhibition prohibits cells to grow
and divide when they come into close
contact with other cells
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Contact inhibition prevents cell
overgrowth by halting the cell cycle
Apoptosis
Apoptosis is programmed cell
death
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The cell go through a series of
events that brings about its
destruction
Both the cell cycle and apoptosis
are normal parts of growth and
development
Apoptosis and cell division are
opposing forces and they keep the
number of cells in the body at an
appropriate level
Apoptosis can be used to shape
an organism or to destroy
abnormal cells
Characteristics of Cancer Cells
Carcinogenesis is the development of
cancer
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Cancer occurs when the cell cycle
is not regulated properly
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Cancer may take decades to
develop before the tumor is visible
Cancers are classified according to
their location:
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Carcinomas are cancers of the
epithelial tissue that lines organs
Sarcomas are cancers of muscle or
connective tissue (bone or
cartilage)
Leukemias are cancers of the blood
Characteristics:
1.
2.
3.
4.
5.
Cancer cells lack
differentiation
Cancer cells have abnormal
nuclei
Cancer cells do not undergo
apoptosis
Cancer cells form tumors
Cancer cells undergo
metastasis and promote
angiogenesis
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A benign tumor is usually
contained with a capsule
and is not invasive
A malignant tumor is one
that has become invasive
and may spread tumor cells
Metastasis is the spread of
cancer cells from its origin
to the the rest of the body
Cancer Treatment and
Prevention
Cancer treatments are aim to either remove the
tumor or to interfere with the ability of the
cancer cells to reproduce
Solid tumors are easily removed and early
detection leads to better prognosis
Chemotherapy and radiation therapy damage
DNA or interfere with the completion of mitosis
The risk of cancer can be reduced by
avoiding smoking, sunbathing,
excessive alcohol comsumption, and
by adopting a better diet
Cigarette smoking accounts for about
30% of all cancer deaths
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90% of lung cancer
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Radiation uses high-energy beams to kill
specific cells within a tumor
Skin cancers are sun-related.
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Chemotherapy is used to kill cancer cells
that have spread throughout the body
Protective diet:
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Vinblastine and Taxol
Tamocifen
Increase consumption of foods
rich in vitamins A and C
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Both types of treatments are also
damaging to other normal cells
Hormonal therapy interferes with the cancer
cells’ reception of an external signal to divide
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Because these vitamins are
antioxidants, they will prevent
the formation of free radicals
that can damage DNA
Avoid salt-cured or pickled foods
Include vegetables from the
cabbage family