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Learning outcomes
• Describe Chromosome structure• Explain Mitosis: Interphase, Prophase,
Metaphase, Anaphase, Telophase• Describe the Significance of mitosis
04/17/23Cell division, Mitosis, cell cycle
2
Why Is Cell Division Important ?
• Cell division is important to multi-celled and single celled organisms, like bacteria and algae.
• All cells go through cell division in what is called the cell cycle.
• Cell cycle starts with cell formation followed by growth and finally ends in the death of the cell.
04/17/23Cell division, Mitosis, cell cycle
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Cell Division• All cells are derived from pre-
existing cells• New cells are produced for growth
and to repair tissues• Differs in prokaryotes (bacteria) and
eukaryotes (protists, fungi, plants, & animals)
04/17/23Cell division, Mitosis, cell cycle
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DNA Replication• DNA must be
copied or replicated before cell division
• Each new cell will then have an identical copy of the DNA
04/17/23Cell division, Mitosis, cell cycle
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Original DNA strand
Two new, identical DNA
strands
Identical Daughter Cells
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Parent Cell
Two identical daughter
cells
Prokaryotic Chromosome
The DNA of prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane
04/17/23 8
Eukaryotic Chromosomes
• All eukaryotic cells store genetic information in chromosomes
• Most eukaryotes have between 10 and 50 chromosomes in their body cells
• Human body cells have 46 chromosomes or 23 identical pairs
04/17/23 9
Compacting DNA into Chromosomes
DNA is tightly coiled around proteins called histones
04/17/23Cell division, Mitosis, cell cycle
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Chromosomes in Dividing Cells
Duplicated chromosomes are called chromatids & are held together by the centromere
04/17/23 11Called Sister Chromatids
Karyotype
• A picture of the chromosomes from a human cell arranged in pairs by size
• First 22 pairs are called autosomes
• Last pair are the sex chromosomes
• XX female or XY male
04/17/23 12
Cell Reproduction
• Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells
• Mitosis & binary fission are examples of asexual reproduction
04/17/23Cell division, Mitosis, cell cycle
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False-Colour EMof Dividing Bacterium
CytoplasmCytoplasm
Division planeDivision plane
Cell wall
Nuclear material
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Yeasts:Asexual Reproduction by Mitosis
• Budding• Nucleus divides by
mitosis• Bud forms on cell• Nucleus moves into bud• Bud separates
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Protozoa:Asexual Reproduction by Mitosis
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New individualsNew individuals
Functions of Mitosis
04/17/23Cell division, Mitosis, cell cycle
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Mitotic Mitotic
cell divisioncell division
Mitotic cell Mitotic cell division & division &
differentiationdifferentiation
OrgansOrgans
TissuesTissues
Five Phases of the Cell CycleCycle• G1 - primary growth phase• S – synthesis; DNA replicated• G2 - secondary growth phase
–collectively these 3 stages are called interphase
• M - mitosis• C - cytokinesis
04/17/23Cell division, Mitosis, cell cycle
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Interphase• Cells spent most time in Interphase, in which the
cell grows and develops.
• During the later part of interphase the cell duplicates all of its chromosomes, and prepares to undergo mitosis.
• When chromosomes duplicate they form 2 chromatids.
• The cells copy chromosomes before mitosis so that the two new cells that are going to be made have an equal amount of chromosomes
04/17/23Cell division, Mitosis, cell cycle
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Interphase - G1 Stage
• 1st growth stage after cell division
• Cells mature by making more cytoplasm & organelles
• Cell carries on its normal metabolic activities
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Interphase – S Stage• Synthesis stage
• DNA is copied or replicated
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Two identical copies of
DNA
Original DNA
Interphase – G2 Stage• 2nd Growth Stage
• Occurs after DNA has been copied
• All cell structures needed for division are made (e.g. centrioles)
• Both organelles & proteins are made
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The Cell Cycle
04/17/23 29
Daughter Cells
DNA Copied
Cells Matur
e
Cells prepare for Division
Cell Divides into Identical cells
Early Prophase• Chromatin in nucleus condenses to form
visible chromosomes• Mitotic spindle forms from fibres in
cytoskeleton or centrioles (animal)
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Chromosomes
Nucleolus Cytoplasm
Nuclear Membrane
Late Prophase
• Nuclear membrane & nucleolus are broken down
• Chromosomes continue condensing & are clearly visible
• Spindle fibers (kinetochores) attach to the centromere of each chromosome
• Spindle finishes forming between the poles of the cell
04/17/23Cell division, Mitosis, cell cycle
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Spindle Fibre attached to Chromosome
Cell division, Mitosis, cell cycle 35
Spindle (Kinetochore) Fibre
Chromosome
Spindle Fibres
• The mitotic spindle form from the microtubules in plants and centrioles in animal cells
• Polar fibers extend from one pole of the cell to the opposite pole
• Spindle (Kinetochore) fibres extend from the pole to the centromere of the chromosome to which they attach
• Asters are short fibers radiating from centrioles
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Metaphase• Chromosomes, attached to the kinetochore fibers,
move to the center of the cell• Chromosomes are now lined up at the equator
04/17/23 38
Pole of the Cell
Equator of Cell
Anaphase
• Occurs rapidly
• Sister chromatids are pulled apart to opposite poles of the cell by Spindle(kinetochore) fibers
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Telophase
• Sister chromatids at opposite poles• Spindle disassembles• Nuclear envelope forms around
each set of sister chromatids• Nucleolus reappears• Cytokinesis occurs• Chromosomes reappear as
chromatin
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Cytokinesis
• Means division of the cytoplasm• Division of cell into two identical halves
called daughter cells• In plant cells, cell plate forms at the
equator to divide cell• In animal cells, cleavage furrow forms to
split cell
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Cytokinesis
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Cleavage furrow in animal cell
Cell plate in plant cell
Name the Mitotic Stages:
46
Interphase
Prophase
MetaphaseAnaphase
Telophase
Name this?
Name this?
04/17/23
Mitosis Animation
04/17/23Cell division, Mitosis, cell cycle
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Name each stage as you see it occur?
Name the Stages of Mitosis:
04/17/23 48
Interphase
Early prophase
Mid-ProphaseLate Prophase
Metaphase
Late Anaphase
Early Anaphase
Early Telophase,
Begin cytokinesis
Late telophase, Advanced cytokinesis
Cell division, Mitosis, cell cycle
Identify the Stages
04/17/23 49
Early, Middle, & Late Prophase
Late Prophase Metaphase Anaphase
Late Anaphase Telophase Telophase & Cytokinesis
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