DISCUSSION ASSIGMENT
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Mader_Essentials_7e_LecturePPT_Ch08_ACCESS.pptxChapter 8
Cellular Reproduction
Essentials of Biology
SEVENTH EDITION
Sylvia S. Mader Michael Windelspecht
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8.1 An Overview of Cellular Reproduction
Multicellular organisms begin life as a single cell.
Humans become trillions of cells because of cellular reproduction.
Reproduction continues as we grow to replace worn-out or damaged tissues.
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Figure 8.1 Cellular Reproduction
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(a): Andersen Ross/Getty Images; (b): Ted Kinsman/Science Source; (c): Biophoto Associates/Science Source; (d): (zygote): Anatomical Travelogue/Science Source; (fetus): Steve Allen/Brand X Pictures/Getty Images
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Cellular Reproduction 1
Asexual reproduction (example Binary fission)
Doesn’t require sperm or egg (required in sexual reproduction)
All cells come from cells.
Cellular reproduction is necessary for the production of both new cells and new organisms.
Two important processes
Growth—cell duplicates its contents (including DNA and organelles)
Cell division—parent cell contents divides into two daughter cells
Both processes heavily regulated
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Cellular Reproduction 2
Chromosomes
DNA replication is the copying of DNA.
Full set is passed to each daughter cell
DNA is packaged into chromosomes.
Thickened complex of DNA and proteins
Allows easier distribution to daughter cells
Chromatin
DNA and associated proteins have the appearance of thin threads.
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Figure 8.2 Chromosome Compaction
DNA is periodically wound around histones to form nucleosomes.
Just before cell division, chromatin condenses into chromosomes.
Humans have 46 chromosomes.
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8.2 The Cell Cycle: Interphase, Mitosis, and Cytokinesis
Orderly sequence of stages that takes place between the time a new cell has arisen to the point where it gives rise to two daughter cells
Interphase
M (Mitotic) phase
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Figure 8.3 The Cell Cycle
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Figure 8.4 Overview of Mitosis
Duplicated chromosomes are composed of sister chromatids joined at the centromere.
Each sister chromatid has identical DNA.
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Interphase 1
Majority of the cell cycle
Time when a cell performs its usual functions
Amount of time varies widely depending on cell
Three stages:
G₁
S—DNA synthesis
G₂
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Interphase 2
Interphase is divided into three stages.
G₁—stage before DNA replication
Cell doubles organelles
Accumulates materials for DNA synthesis
Makes decision whether to divide or not
G₀—arrested—does not go on to divide
S—DNA synthesis
Results in each chromosome being composed of two sister chromatids
G₂—stage following DNA synthesis
Extends to onset of mitosis
Synthesizes proteins needed for cell division
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Cell Division Occurs in the M (Mitotic) Phase
Cell division occurs.
Encompasses
Division of nucleus (mitosis)
Creates two identical daughter nuclei
Division of cytoplasm (cytokinesis)
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M (Mitotic) Phase
Distributes duplicated nuclear contents of parent cell equally to daughter cells
Each sister chromatid has the same genetic information.
Daughter chromosomes—separated sister chromatids
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Daughter Nuclei
Daughter nuclei produced by mitosis are genetically identical to each other and to the parent nucleus.
Every animal has an even number of chromosomes—each parent contributes half of the chromosomes to the new individual.
In drawings, colors may be used to indicate chromosomes contributed by the male or female parent.
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Moving the Chromosomes
Spindle
Most eukaryotic cells rely on this structure to pull chromatids apart.
Part of the cytoskeleton
Spindle fibers are made of microtubules
Centrosome—primary microtubule organizing center
Spindle fibers may overlap at the spindle equator or attach to duplicated chromosomes.
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Phases of Mitosis in Animal and Plant Cells
Mitosis is a continual process traditionally divided into four phases:
Prophase—chromosomes are visible under microscope in condensed pairs
Metaphase—chromosomes line up along equatorial plate (middle)
Anaphase—chromosomes are pulled to opposite poles of cell (apart)
Telophase and Cytokinesis—two distinct cells are visible under the microscopes.
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Figure 8.5 Phases of Mitosis in Animal Cells 1
Interphase
During interphase, the eukaryotic cell duplicates the contents of the cytoplasm, and DNA replicates in the nucleus. The duplicated chromosomes are not yet visible. A pair of centrosomes is outside the nucleus.
Prophase
During prophase, the chromosomes are condensing. Each consists of two sister chromatids held together at a centromere. Outside the nucleus, the spindle begins to assemble between the separating centrosomes.
Prophase continues with the disappearance of the nucleolus and the breakdown of the nuclear envelope. Spindle fibers from each pole attach to the chromosomes at specialized protein complexes on either side of each centromere. During attachment, a chromosome first moves toward one pole and then toward the other pole.
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(all): ©Ed Reschke
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Figure 8.5 Phases of Mitosis in Animal Cells 2
Metaphase
During metaphase, the chromosomes are aligned at the spindle equator midway between the spindle poles. The spindle fibers on either side of a chromosome extend to opposite poles of the spindle. Unattached spindle fibers reach beyond the equator and overlap.
Anaphase
During anaphase, the sister chromatids separate and become daughter chromosomes. As the spindle fibers attached to the chromosomes disassemble, each pole receives a set of daughter chromosomes. The spindle poles move apart as the unattached spindle fibers slide past one another. This contributes to chromosome separation.
Telophase and Cytokinesis
During telophase, the spindle disappears as new nuclear envelopes form around the daughter chromosomes. Each nucleus contains the same number and kinds of chromosomes as the original parent cell. Remnants of spindle fibers are still visible between the two nuclei. Division of the cytoplasm begins.
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(all): ©Ed Reschke
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Phases of Mitosis in Animal Cells
Although mitosis is divided into phases, it is a continuous process.
DNA is replicated before mitosis begins.
Each chromosome consists of two sister chromatids attached at a centromere.
Red chromosomes are from one parent, and blue are from the other parent.
Mitosis is usually followed by cytokinesis.
Division of the cytoplasm
Begins during telophase and continues after the daughter nuclei have formed
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Mitosis Differs in Plants and Animals
Plant and animal cells differ.
Plant—have centrosomes but lack centrioles
Animal—each centrosome has two centrioles and an aster (array of microtubules)
Cell membrane in plants form from center outward along a cell plate
Cell membrane in animals forms through a cleavage furrow (outer membrane toward the center).
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Figure 8.6 Comparing Mitosis in a Plant and Animal Cell 1
Nucleolus has disappeared, and duplicated chromosomes are visible. Centrosomes begin moving apart, and spindle is in process of forming.
The kinetochore of each chromatid is attached to a kinetochore spindle fiber. Polar spindle fibers stretch from each spindle pole and overlap.
Metaphase
Centromeres of duplicated chromosomes are aligned at the metaphase plate (center of fully formed spindle). Kinetochore spindle fibers attached to the sister chromatids come from opposite spindle poles.
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(prophase, metaphase, anaphase, telophase): Kent Wood/Science Source; (prometaphase): ©Ed Reschk
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Figure 8.6 Comparing Mitosis in a Plant and Animal Cell 2
Anaphase
Sister chromatids part and become daughter chromosomes that move toward the spindle poles. In this way, each pole receives the same number and kinds of chromosomes as the parent cell.
Telophase
Daughter cells are forming as nuclear envelopes and nucleoli reappear. Chromosomes will become indistinct chromatin.
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(prophase, metaphase, anaphase, telophase): Kent Wood/Science Source; (prometaphase): ©Ed Reschk
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Cytokinesis in Animal and Plant Cells
Cytokinesis
Accompanies mitosis in most but not all cells
Mitosis with cytokinesis results in a multinucleated cell
Muscle cells in vertebrate animals
Embryo sac in flowering plants
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Cytokinesis in Animal Cells
Cleavage furrow forms as anaphase ends.
Contractile ring, a band of actin filaments, forms a constriction.
Like pulling a drawstring
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(top): National Institutes of Health (NIH)/USHHS; (bottom): Steve Gschmeissner/Brand X Pictures/Science Photo Library/Getty Images
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Cytokinesis in Plant Cells
Plant cells
Rigid cell wall prevents furrowing
Involves building of new plasma membrane and cell walls between daughter cells
Golgi apparatus produces vesicles.
Cell plate—newly formed plasma membrane
New membrane releases molecules that form new plant cell walls
Biophoto Associates/Science Source
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8.3 The Cell Cycle Control System
Cell cycle must be controlled
Ensures that the stages occur in order and that the cycle continues only when the previous stage is successfully completed
Cell cycle checkpoints
Three of the many
G₁ checkpoint
G₂ checkpoint
Mitotic stage checkpoint
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Cell Cycle Checkpoints
G₁ checkpoint
Cell committed to divide after this point
Can enter G₀ if checkpoint not passed
Proper growth signals must be present to pass
DNA integrity checked—if repair is not possible, apoptosis occurs
G₂ checkpoint
Verifies that DNA replicated
DNA damage repaired
Mitotic stage checkpoint
Between metaphase and anaphase
All chromosomes must be attached to spindle to pass.
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Figure 8.9 Cell Cycle Checkpoints
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Internal and External Signals
Signal—a molecule that stimulates or inhibits an event
External signals come from outside the cell.
Internal signals come from inside the cell.
Kinases remove a phosphate from ATP and add it to other molecules.
Cyclins are internal signals present only during certain stages of the cell cycle.
Destruction of cyclin at the appropriate time is necessary for normal cell cycle progression.
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Cell Cycle Signals
External signals
Epidermal growth factor (EGF) stimulates skin near an injury to finish cell cycle and repair injury.
Hormone estrogen stimulates lining of the uterus to divide and prepare for egg implantation.
Contact inhibition—cells stop dividing when they touch
Cells divide about 70 times in culture and then die.
Due to shortening of telomeres
Telomere—repeating DNA sequence at end of chromosome
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Apoptosis
Programmed cell death
Remaining cell fragments engulfed by white blood cells
Unleashed by internal or external signals
Helps keep number of cells at appropriate level
Normal part of growth and development
Tadpole tail
Webbing between human digits
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Figure 8.10 Apoptosis 1
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Figure 8.10 Apoptosis 2
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8.4 Cell Cycle and Cancer
Cell cycle is regulated by signals that inhibit or promote cell cycle.
Cancer may result from imbalance.
Cancer is a disease of the cell cycle in which cellular reproduction occurs repeatedly without end.
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Figure 8.11 Development of Cancer
Cell (red) acquires a mutation for repeated cell division.
New mutations arise, and one cell (teal) has the ability to start a tumor.
Cancer in situ. The tumor is at its place of origin. One cell (purple) mutates further.
Cells have gained the ability to invade underlying tissues by producing a proteinase enzyme.
Cancer cells now have the ability to invade lymphatic and blood vessels.
New metastatic tumors are found some distance from the original tumor.
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Genetic Control of the Cell Cycle
Proto-oncogenes code for proteins that promote the cell cycle and inhibit apoptosis. They are often likened to the gas pedal of a car because they accelerate the cell cycle.
Tumor suppressor genes code for proteins that inhibit the cell cycle and promote apoptosis.
When proto-oncogenes mutate, they become cancer-causing genes called oncogenes.
When tumor suppressor genes mutate, their products no longer inhibit the cell cycle or promote apoptosis.
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Figure 8.12 Role of Proto-oncogenes and Tumor Suppressor Genes in the Cell Cycle
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Other Genetic Changes and Cancer
Absence of telomere shortening
Chromosomal rearrangements
When the chromosomes of cancer cells become unstable, portions of the DNA double helix may be lost, duplicated, or scrambled. For example, a portion of a chromosome may break off and reattach to another chromosome. These events are called translocations.
Other cell cycle genes associated with cancer:
BRCA1 and BRCA2
RB gene
RET gene
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8.5 Characteristics of Cancer
Characteristics of cancer cells
Carcinogenesis—development of cancer
Cancer cells lack differentiation—do not contribute to body function
May be immortal—divide repeatedly
Have abnormal nuclei with abnormal number of chromosomes
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Figure 8.14 Cancer Cells
Cancer cells
Do not undergo apoptosis
Form tumors—do not respond to inhibitory signals
Undergo metastasis (cells travel to start new tumors) and angiogenesis (form new blood vessels to nourish themselves)
Benign—contained within a capsule
Malignant—invasive and may spread
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N. Kedersha/Science Source
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Figure 8.15 Development of Breast Cancer
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Cancer Treatment
Either remove tumor or interfere with the ability of cancer cells to reproduce
As rapidly dividing cells, they are susceptible to radiation therapy and chemotherapy.
Damages DNA or some aspect of mitosis
Leads to side effects
Hormone therapy is designed to prevent cells from receiving signals for continued growth and division.
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Prevention of Cancer
Protective behaviors
Avoid smoking—accounts for about 30% of all cancer deaths
Avoid sun exposure—major factor in development of most dangerous type of skin cancer, melanomas
Heavy drinkers are prone to particular cancers.
Protective diet
Weight loss can reduce cancer risk.
Increase consumption of foods rich in vitamins A and C.
Avoid salt-cured or pickled foods.
Include cabbage family members in the diet.
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Figure 8.16 The Right Diet Helps Prevent Cancer
(leafy greens): Ingram Publishing/SuperStock; (blueberries): Purestock/SuperStock; (oranges): sanmai/Getty Images; (broccoli): Mark Steinmetz/McGraw Hill
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End of Main Content
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Figure 8.1 Cellular Reproduction - Text Alternative
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The details of the panels are as follows:
a. Children grow: A woman hugs a baby girl.
b. Tissue repair: A set of nine photos shows the sequential healing of a wound.
c. Amoebas reproduce: The cell of Amoeba ruptures into two.
d. Zygotes develop: Human zygote with a fetus in the womb.
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Figure 8.2 Chromosome Compaction - Text Alternative
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a. At the top, a duplicated and condensed chromosome shows two labels including sister chromatids and centromere. Further, looped chromatin and zigzag chromatins are shown. Next, chromatin is coiled around specialized proteins called histones to form nucleosomes.
b. The micrograph of a DNA strand shows nucleosomes. They appear as beads on a string.
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Figure 8.3 The Cell Cycle - Text Alternative
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Interphase includes stages G1, S, and G2, leading to stage M (Mitosis). G0 stage is also mentioned in the interphase. In the G1 phase, growth occurs as organelles double. In the S phase, DNA replication occurs as chromosomes duplicate. In the G2 phase, growth occurs as cell prepares to divide.
In stage M, mitosis and cytokinesis occur including steps prophase, metaphase, anaphase, and telophase, along with cytokinesis. After completion of the M stage, two cells are formed.
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Figure 8.4 Overview of Mitosis - Text Alternative
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A chromosome consisting of one chromatid converts into duplicated chromosome with two sister chromatids, connected with a centromere, during DNA replication. The duplicated chromosome with two sister chromatids converts into two daughter chromosomes consisting of one chromatid, during mitosis.
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M (Mitotic) Phase - Text Alternative
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A chromosome consisting of one chromatid converts into duplicated chromosome with two sister chromatids, connected with a centromere, during DNA replication. The duplicated chromosome with two sister chromatids converts into two daughter chromosomes consisting of one chromatid, during mitosis.
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Cell Division Occurs in the M (Mitotic) Phase - Text Alternative
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Interphase includes stages G1, S, and G2, leading to stage M (Mitosis). G0 stage is also mentioned in the interphase. In the G1 phase, growth occurs as organelles double. In the S phase, DNA replication occurs as chromosomes duplicate. In the G2 phase, growth occurs as cell prepares to divide.
In stage M, mitosis and cytokinesis occur including steps prophase, metaphase, anaphase, and telophase, along with cytokinesis. After completion of the M stage, two cells are formed.
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Figure 8.5 Phases of Mitosis in Animal Cells 1 - Text Alternative
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The stages are discussed as follows:
G 1, S, and G 2 stages are associated with the interphase of the cell cycle. During interphase, the eukaryotic cell duplicates the contents of the cytoplasm, and DNA replicates in the nucleus. The cell in this stage shows labels including centrosome, centrioles, nucleolus, chromatin, nuclear envelope, and plasma membrane.
The M phase of the cell cycle is divided into four phases along with cytokinesis.
Prophase: During prophase, the chromosomes are condensing. Each consists of two sister chromatids held together at a centromere. At this stage, the cell shows the parts including early mitotic spindle, centrosome, centromere, and chromosome with two sister chromatids. Next, prophase continues with the disappearance of the nucleolus and the breakdown of the nuclear envelope. At this stage, the cell shows parts including spindle fibers and nuclear envelope fragments. The chromosome area is also easily distinguished in two micrographs magnified 250 times.
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Figure 8.5 Phases of Mitosis in Animal Cells 2 - Text Alternative
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The stages are discussed as follows:
Metaphase: During metaphase, the chromosomes are aligned at the spindle equator midway between the spindle poles. Aster and chromosomes at spindle equator are easily seen in the micrograph magnified at 250 times.
Anaphase: During anaphase, the sister chromatids separate and become daughter chromosomes that are easily seen in the dividing cell and the micrograph magnified at 250 times.
Telophase and cytokinesis. During telophase, the spindle disappears as new nuclear envelopes form around the daughter chromosomes. Each nucleus contains the same number and kinds of chromosomes as the original parent cell. Cleavage furrow and nuclear envelope formation are seen in the cell and the micrograph magnified at 250 times.
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Figure 8.6 Comparing Mitosis in a Plant and Animal Cell 1 - Text Alternative
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Prophase: During prophase, the chromosomes are condensing. Each consists of two sister chromatids held together at a centromere. The plant cell at 900 times magnification shows cell wall and chromosomes and the animal cell shows duplicated chromosome, centromere, and spindle fibers forming.
Prophase continues with the disappearance of the nucleolus and the breakdown of the nuclear envelope. The plant cell at 500 times magnification and the animal cell show distinct spindle pole.
Metaphase: During metaphase, the chromosomes are aligned at the spindle equator midway between the spindle poles. The plant cell at 900 times magnification shows spindle fibers and the animal cell shows chromosomes at metaphase plate.
Anaphase: During anaphase, the sister chromatids separate and become daughter chromosomes. The plant cell at 900 times magnification and the animal cell show daughter chromosomes.
Telophase and cytokinesis: During telophase, the spindle disappears as new nuclear envelopes form around the daughter chromosomes. Each nucleus contains the same number and kinds of chromosomes as the original parent cell. The plant cell at 900 times magnification shows a cell plate while the animal cell shows cleavage furrow and nucleolus.
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Figure 8.6 Comparing Mitosis in a Plant and Animal Cell 2 - Text Alternative
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Prophase: During prophase, the chromosomes are condensing. Each consists of two sister chromatids held together at a centromere. The plant cell at 900 times magnification shows cell wall and chromosomes and the animal cell shows duplicated chromosome, centromere, and spindle fibers forming.
Prophase continues with the disappearance of the nucleolus and the breakdown of the nuclear envelope. The plant cell at 500 times magnification and the animal cell show distinct spindle pole.
Metaphase: During metaphase, the chromosomes are aligned at the spindle equator midway between the spindle poles. The plant cell at 900 times magnification shows spindle fibers and the animal cell shows chromosomes at metaphase plate.
Anaphase: During anaphase, the sister chromatids separate and become daughter chromosomes. The plant cell at 900 times magnification and the animal cell show daughter chromosomes.
Telophase and cytokinesis: During telophase, the spindle disappears as new nuclear envelopes form around the daughter chromosomes. Each nucleus contains the same number and kinds of chromosomes as the original parent cell. The plant cell at 900 times magnification shows a cell plate while the animal cell shows cleavage furrow and nucleolus.
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Cytokinesis in Animal Cells - Text Alternative
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The top micrograph at 4000 times magnification and the diagram show a distinct cleavage furrow. The diagram also shows the contractile ring that is visible in the second micrograph. The last diagram shows the deepening of the cleavage and eventually tends to separate the membrane in two by the movement of the cell cytoplasm towards the centripetal direction.
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Figure 8.9 Cell Cycle Checkpoints - Text Alternative
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The checkpoints of the cell cycle are as follows:
G1 checkpoint: The G1 checkpoint is present at the end of the G1 phase, before the transition to the S phase. Here, apoptosis can occur if DNA is damaged beyond repair.
G2 checkpoint: It ensures that mitosis will not occur until DNA is replicated.
M checkpoint: At this checkpoint, mitosis stops until the chromosomes are properly aligned.
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Figure 8.10 Apoptosis 1 - Text Alternative
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First is a group of normal cells. Next, a normal cell rounds up, and the nucleus collapses.
Then, the chromatin condenses and the DNA breaks into fragments.
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Figure 8.10 Apoptosis 2 - Text Alternative
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The plasma membrane blisters and blebs form. Diagram shows the blebs. Finally, the cell breaks into fragments. The micrograph of apoptotic cell magnified at 2500 times shows cell and DNA fragments.
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Figure 8.11 Development of Cancer - Text Alternative
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The steps are marked from top to bottom as:
Only one mutation in red appears across the yellow epithelial cells.
Two mutations appear across the epithelial cells with one teal cell at the center of a few red cells.
Three mutations appear just above the lymphatic and blood vessels, forming a tumor. The illustration shows a pile of teal cells with one purple cell at the bottom.
An invasive tumor, that is, a pile of purple cells appears.
The malignant tumor, which is a pile of purple cells appears approaching the lymphatic and blood vessel appears.
A purple cell appears in the lymphatic vessel. The distant tumor, which is a pile of purple cells appears invading the lymphatic vessel.
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Figure 8.12 Role of Proto-oncogenes and Tumor Suppressor Genes in the Cell Cycle - Text Alternative
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a. It demonstrates how a growth factor binds to a cell membrane-attached receptor. The phosphorylation of signaling protein, which leads to activated signaling protein, supports the activity of receptors. Labels include signaling protein, activated signaling protein, and phosphate.
b. Growth factor binds to receptor and activates proto-oncogenes through cell-signaling pathway. Proto-oncogene codes for a protein that promotes the cell cycle. If a proto-oncogene mutates, the resulting oncogenes may lead to uncontrolled cell division. Tumor suppressor gene codes for a protein that inhibits the cell cycle. Mutant tumor suppressor genes can lose this function. Labels are activation of proto-oncogene, promotion of cell-cycle, expression of tumor suppressor, and inhibition of cell cycle.
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Other Genetic Changes and Cancer - Text Alternative
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The ABL and BCR genes are located on the long arms of chromosomes 9 and 22 respectively.
The translocation of ABL gene from chromosome 9 to chromosome 22 creates the Philadelphia chromosome that contains the BCR-ABL oncogene.
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Figure 8.14 Cancer Cells - Text Alternative
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Yellow and red cells are labeled cancer cells and the green cells on either side are labeled normal cells.
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Figure 8.15 Development of Breast Cancer - Text Alternative
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A benign tumor in the breast is developed from a single mutated cell. The tumor becomes malignant and invades nearby tissue. The cancer cells travel through lymphatic and blood vessels, and metastatic tumors form.
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