Mitosis, Meiosis and the Cell Cycle - · PPT file · Web view ·...
Transcript of Mitosis, Meiosis and the Cell Cycle - · PPT file · Web view ·...
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Hand in your homework please!
• Detach the first section (including exam questions) and put your name on it!
• Homework for MONDAY:Complete the section on ‘Methods of
studying cells’ INCLUDING exam questions to hand in on MONDAY.
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The Cell Cycle and Mitosis
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Cell Division
• Mitosis is a type of cell division that produces genetically identical copies of cells.
• Not all cells can divide.
• What types of cells DO divide?
• Cells that can divide go through a CELL CYCLE.
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The Cell Cycle
Mitosis is only a small part of the ‘life’ of a cell. The process from one cell division to the next is known as the cell cycle.
There are 4 parts to the cell cycle:Gap 1SynthesisGap 2Mitosis
These stages are all parts of interphase.
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The cell cycle
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Can you think of 3 reasons why mitosis is important?
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A bit of background…
• A chromosome is a strand of DNA.• After S-phase (DNA replication), identical
copies of chromosomes remain attached – SISTER CHROMATIDS joined at the CENTROMERE.
DNA replication
Chromosome Sister chromatids
Centromere
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• The chromosomes can’t be seen most of the time – they are tangled strands of DNA.
• During cell division, the chromosomes condense – they coil up, aided by a number of proteins.
Reminder:
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Mitosis
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Interphase• The cell is
engaged in metabolic activity in preparation for mitosis
• Chromosomes are not visible under the light microscope
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Prophase• Chromosomes
condense and become visible under the light microscope
• The nucleolus disappears
• Centrioles begin moving to opposite ends of the cell and spindle fibres extend from the centrioles
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Metaphase
• The nuclear membrane dissolves, marking the beginning of metaphase.
• Spindle fibres attach to the centromere of each chromosome.
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Metaphase• Spindle fibres align
the chromosomes along the equator of the cell
• This helps ensure that during the next phase, when the chromosomes are separated, each new nucleus will receive one copy of each chromosome
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Anaphase
• The sister chromatids separate at the centromeres and move to opposite sides (poles) of the cell
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Telophase• Chromatids arrive at
opposite poles of the cell, and nuclear membranes form around them
• The chromosomes are no longer visible under the light microscope
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Another way to remember the stages…
Invisible
Present
Middle
Apart
Two
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CYTOKINESIS
• The cytoplasm divides so two cells are formed.
• The two daughter cells are genetically identical to each other, and to the parent cell.
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Try to identify the stages of mitosis in the two photomicrographs on the back of your sheet.
Write a sentence for each one to explain how you reached your answer.
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Stages of the cell cycle