Chapter 8 Cell Cycle - Mitosis. WHAT CELL REPRODUCTION ACCOMPLISHES Cell Reproduction – –may...
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Transcript of Chapter 8 Cell Cycle - Mitosis. WHAT CELL REPRODUCTION ACCOMPLISHES Cell Reproduction – –may...
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Chapter 8
Cell Cycle - Mitosis
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WHAT CELL REPRODUCTION ACCOMPLISHESCell Reproduction –
– may result in the birth of new organisms
– more commonly involves the production of new cells
• When a cell undergoes reproduction, or cell division, two “daughter” cells are produced that are genetically identical
– to each other
– to the “parent” cell.
Cell Theory – Cells Come From Cells
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• Cell division plays important roles in the lives of organisms.
• Cell division
– replaces damaged or lost cells
– permits growth
– allows for reproduction
WHAT CELL REPRODUCTION ACCOMPLISHES
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• Before a cell divides, it duplicates all of its chromosomes through the process of replication, resulting in two copies called sister chromatids containing identical genes.
• Two sister chromatids are joined together tightly at a narrow “waist” called the centromere.
Eukaryotic Chromosomes
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• When the cell divides, the sister chromatids of a duplicated chromosome separate from each other.
• Once separated, each chromatid is
– considered a full-fledged chromosome
– identical to the original chromosome.
Eukaryotic Chromosomes
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Figure 8.UN01
Duplicationof all
chromosomes
Geneticallyidentical
daughter cells
Distribution viamitosis
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• In asexual reproduction,
– single-celled organisms reproduce by simple cell division in which the parent cell and daughter cells have identical DNA
– there is no fertilization of an egg by a sperm.
• Some multicellular organisms, such as sea stars, can grow new individuals from fragmented pieces.
• Growing a new plant from a clipping is another example of asexual reproduction.
• Producing more skin cells is yet another example of asexual reproduction.
WHAT CELL REPRODUCTION ACCOMPLISHES
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• Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis.
• Thus, sexually reproducing organisms use
– meiosis for reproduction
– mitosis for growth and maintenance.
WHAT CELL REPRODUCTION ACCOMPLISHES
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• Chromosomes are
– made of chromatin, fibers composed of roughly equal amounts of DNA and protein molecules
– not visible in a cell until cell division occurs.
Eukaryotic Chromosomes
Each eukaryotic chromosome contains one very long DNA molecule, typically bearing thousands of genes.
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Figure 8.3
Chromosomes
LM
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Duplicated chromosomes(sister chromatids)
TE
M
Tight helical fiber
Thick supercoil
TE
M
Centromere
Nucleosome
“Beads on a string”
Histones
DNA double helix• The DNA in a cell is packed into an elaborate, multilevel system of coiling and folding.
• Histones are proteins used to package DNA in eukaryotes.
• Nucleosomes consist of DNA wound around histone molecules.
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TE
M
Nucleosome
“Beads on a string”
Histones
DNA double helix
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Figure 8.2
Number of chromosomes in body cells
Indian muntjac deer
Species
Opossum
Koala
Human
Mouse
Giraffe
Buffalo
Dog
Red viscacha rat
Duck-billed platypus
102
78
60
54
46
40
30
22
16
6
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The Cell Cycle
• A cell cycle is the ordered sequence of events that extends
– from the time a cell is first formed from a dividing parent cell to its own division into two cells.
• The cell cycle consists of two distinct phases:
1. interphase
2. the mitotic phase.
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Figure 8.UN03
Interphase Cell growth and
chromosome duplication
G2
Mitotic(M) phase
S phase DNA synthesis; chromosome duplication
G1
Genetically identical“daughter”cells
Cytokinesis (division ofcytoplasm)
Mitosis (division ofnucleus)
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• Most of a cell cycle is spent in interphase.
• During interphase a cell
– performs its normal functions
– Replicates all of its DNA – sister chromatids
– doubles everything in its cytoplasm
– grows in size
The Cell Cycle
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• Interphase can be broken down into 3 distinct phases
1. G1 phase – cells increase in size, make new proteins and organelles
2. S phase – chromosomes replicate, DNA synthesis
3. G2 phase – completion of organelle production
The Cell Cycle - Interphase
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• The mitotic (M) phase includes two overlapping processes:
1. mitosis, in which the nucleus and its contents divide evenly into two daughter nuclei
2. cytokinesis, in which the cytoplasm is divided in two
The Cell Cycle
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Mitosis and Cytokinesis
• During mitosis the mitotic spindle, a football-shaped structure of microtubules, guides the separation of two sets of sister chromatids.
• Spindle microtubules grow from structures within the cytoplasm called centrosomes.
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• Mitosis consists of four distinct phases:
1. Prophase
2.Metaphase
3.Anaphase
4.Telophase
Mitosis and Cytokinesis
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© 2013 Pearson Education, Inc.
Bioflix Animation: Mitosis
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1. Prophase
– Changes occur in nucleus and cytoplasm
– Chromatin fibers coil in the nucleus into visible chromosomes
– Each chromosome exists as 2 identical sister chromatids connected at the centromere
– Microtubules start to grow from each centrosome and the centrosomes move away from each other
– Nuclear envelope breaks into pieces
– Spindle microtubules attach to the centromeres of the chromosomes and move them toward the center of the cell.
Mitosis and Cytokinesis
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Figure 8.7a
Nuclearenvelope
Plasmamembrane
Chromosome(two sister chromatids)
Spindle microtubules
Fragments of nuclear envelopeCentrosome
Centromere
Early mitotic spindle
Centrosomes (with centriole pairs) Chromatin
PROPHASEINTERPHASE
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1.Metaphase
– Mitotic spindle is fully formed
– Chromosomes line up between the two poles of the spindle (between the two centrosomes)
– Microtubules attached to the centromeres play tug of war keeping the chromosomes in the middle of the cell.
Mitosis and Cytokinesis
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1.Anaphase
– Sister chromatids separate and move toward opposite poles of the cell as the spindle microtubules shorten
– Microtubules not attached to chromosomes get longer and elongate the cell.
Mitosis and Cytokinesis
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Figure 8.7b
ANAPHASEMETAPHASE TELOPHASE AND CYTOKINESIS
Spindle Daughterchromosomes
Cleavagefurrow
Nuclearenvelopeforming
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1.Telophase and Cytokinesis
– Chromosomes have reached the opposite ends of the cell
– Nuclear envelope forms
– Chromosomes uncoil
– Spindle dissapears
– Cytoplasm divides
– Cell pinches in two (cleavage furrow in animals)
Mitosis and Cytokinesis
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• Cytokinesis usually
– begins during telophase,
– divides the cytoplasm
– is different in plant and animal cells.
Mitosis and Cytokinesis
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• In animal cells, cytokinesis
– is known as cleavage
– begins with the appearance of a cleavage furrow, an indentation at the equator of the cell.
Mitosis and Cytokinesis
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Figure 8.8aa
Cleavage furrowContracting ring ofmicrofilaments
Daughter cells
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• In plant cells, cytokinesis begins when vesicles containing cell wall material collect at the middle of the cell and then fuse, forming a membranous disk called the cell plate.
Mitosis and Cytokinesis
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Figure 8.8ba
Wall of parent cellCell plateforming Daughter nucleus
LM
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Cancer Cells: Growing Out of Control
• Normal plant and animal cells have a cell cycle control system that consists of specialized proteins called cyclins, which send “stop” and “go-ahead” signals at certain key points during the cell cycle.
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What Is Cancer?
• Cancer is a disease of the cell cycle.
• Cancer cells do not respond normally to the cell cycle control system.
• Cancer begins when a normal cell undergoes transformation in which a mutation in the genetic code (DNA) occurs. This mutation interferes with the production of proteins vital in the cell cycle control system.
• Cancer cells can form tumors, abnormally growing masses of body cells.
• If the abnormal cells remain at the original site, the lump is called a benign tumor.
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• The spread of cancer cells beyond their original site of origin is metastasis.
• Malignant tumors can
– spread to other parts of the body and
– interrupt normal body functions.
• A person with a malignant tumor is said to have cancer.
What Is Cancer?
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Figure 8.9
A tumor growsfrom a singlecancer cell.
Cancer cells invadeneighboring tissue.
Metastasis: Cancercells spread throughlymph and bloodvessels to other partsof the body.
Glandulartissue
Bloodvessel
Tumor
Lymphvessels
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Cancer Treatment
• Cancer treatment can involve
– radiation therapy, which damages DNA and disrupts cell division, and
– chemotherapy, the use of drugs to disrupt cell division.
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Cancer Prevention and Survival
• Certain behaviors can decrease the risk of cancer:
– not smoking
– exercising adequately
– avoiding exposure to the sun
– eating a high-fiber, low-fat diet
– performing self-exams
– regularly visiting a doctor to identify tumors early
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THE END