Overview of Division Mechanisms zMitosis and Meiosis are two nuclear division mechanisms zMitosis...
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Transcript of Overview of Division Mechanisms zMitosis and Meiosis are two nuclear division mechanisms zMitosis...
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Overview of Division Mechanisms
Mitosis and Meiosis are two nuclear division mechanisms
Mitosis Somatic cells- body cells
Growth and repair
Meiosis In germ cells- gonads
Gametes- sperm and egg
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Chromosomes
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Before a cell starts dividing, the chromosomes are duplicated This process
produces sister chromatids
Centromere
Sister chromatids
Figure 8.4B
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When the cell divides, the sister chromatids separate
Two daughter cells are produced
Each has a complete and identical set of chromosomes
Centromere Sister chromatids
Figure 8.4C
Chromosomeduplication
Chromosomedistribution
todaughter
cells
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Mitosis and Chromosome Number
Chromosome number: sum total of chromosomes in somatic cells
Chromosomes are in pairs Humans 23 pairs ( one pair from mom,one
from dad)
2n “diploid” ( 46 -human)
1n “haploid” (germ cells, 23 -human)
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The Cell Cycle
A diploid cell produces 2 diploid daughter cells
Two phases in cell cycle
InterphaseLongest phase
Increase in mass, doubles components, and duplicates DNA
MitosisNuclear division
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Interphase
G1
“Gap” - cell growth before DNA replication
S
“Synthesis” - DNA replication
G2
“Second Gap” - preparation for division
M Mitosis
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The Cell Cycle
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Mitosis
Four stages
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis Cytoplasmic division
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INTERPHASE PROPHASE
Centrosomes(with centriole pairs)
Chromatin
Nucleolus Nuclearenvelope
Plasmamembrane
Early mitoticspindle
Centrosome
CentrosomeChromosome,consisting of twosister chromatids
Fragmentsof nuclearenvelope
Kinetochore
Spindlemicrotubules
Figure 8.6
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METAPHASE TELOPHASE AND CYTOKINESIS
Metaphaseplate
Spindle Daughterchromosomes
Cleavagefurrow
Nucleolusforming
Nuclearenvelopeforming
ANAPHASE
Figure 8.6 (continued)
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StagesofMitosis
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Cell at Interphase
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Prophase
Chromosomes are visible
Spindle apparatus formsCentrioles move apart to opposite
poles
Microtubules in two sets
Extend from end and overlap in center
Nuclear envelope breaks up
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Prophase
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Metaphase
Chromosomes interact with
microtubules on spindle apparatus Attachment at centromeres
•Kinetochore
Microtubules pull on chromosomes
Orientation of sister chromatids to opposite poles
Chromosomes align midway between the poles
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Metaphase
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Anaphase
Separation of sister chromatids Movement toward opposite poles
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Telophase
Chromosomes arrive at spindle poles Chromosomes return to threadlike forms
New nuclear membranes form
Two nuclei form
Cytokinesis Division of cytoplasm
Forms 2 cells
Once two nuclei form, mitosis is finished
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Anaphase to Interphase
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Division of the Cytoplasm
“Cytokinesis”
Between late Anaphase and end of Telophase
Cell plate forms in plantsVesicles fuse
Cleavage furrow forms in animalsDepression forms at cell’s midsection
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Cytoplasmic Division of a Plant Cell
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Cytoplasmic Division of an Animal Cell
Cleavage furrow
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Levels of Organization in Metaphase Chromosome
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Levels of Organization in Metaphase Chromosome
A nucleosome
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In Conclusion
A parent cell provides each daughter cell with hereditary instructions
Eukaryotes divide by mitosis or meiosis and Prokaryotes divide by binary fission
Each chromosome is one DNA molecule with proteins attached
Cells with a diploid number (2n) contain two of each kind of chromosome
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In Conclusion
Mitosis divides the nucleus into two equivalent nuclei
Mitosis is the basis of growth, tissue repair, and cell replacements among multicelled eukaryotes
Mitosis can be the method of asexual reproduction among single-celled eukaryotes
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In ConclusionThe cell cycle starts when a new cell
formsThe cell cycle includes Interphase and
MitosisA duplicated chromosome has two DNA
molecules attached at the centromereThe phases of Mitosis are Prophase,
Metaphase, Anaphase, and TelophaseCytoplasmic divisions differ among
animals and plants