Post on 08-Jun-2020
Cell Cycle and Mitosis
Organization of the Process of Cell Division!
What’s Happening in This Picture???
❖ Cells are undergoing various stages of the cell division. ❖ Cell Division Happens at Different Stages
Types of Cell Division
• Binary Fission – Prokaryotic Cell Division
• Mitosis – Eukaryotic Cell Division
• Meiosis – Production of sex cells !
– Two Main Stages – Mitosis and cytokinesis
• Cell cycle is a series of events that cells go through as they grow and divide. !
• During cell cycle: • Cell grows • Prepares for
division. • Divides to form
two daughter cells
Stages of the Cell Cycle
• Is interphase part of mitosis? – NO!!! !
• What percentage of time do cells spend in each phase? – Interphase =
90-95% – Mitosis = 5-10%
Stages of the Cell Cycle
❖ Mitosis is a short but important part of the Cell Cycle
Stages of Interphase
• G0 (Gap0)
– Cell leaves the cell cycle and quit dividing. – Temporary or permanent resting period. – Ex: When cell that has reached an end stage
of development and will no longer divide (e.g. neuron).
Stages of Interphase
• G1 (Gap1) – Cells increase in size. – Produce RNA and synthesize proteins. – G1 Checkpoint ensures that everything is
ready for DNA synthesis. • Cell cycle control mechanism
Stages of Interphase
• S (Synthesis) – DNA replication occurs during this phase. – Once a cell enters this stage, it completes
rest of cell cycle.
Stages of Interphase
• S (Synthesis) – DNA replication occurs during this phase. !
• G2 (Gap2)
– Gap between DNA synthesis and mitosis. – Cell continues to grow and produce proteins and
organelles required for cell division. – G2 Checkpoint determines if the cell can now
proceed to enter M Phase and divide. – Shortest of three phases of interphase
Stages of Mitosis
• There are 4 phases: – Prophase – Metaphase – Anaphase – Telophase
Prophase
• 50-60% of mitosis
Prophase
!• Chromosomes start to become visible,
– Chromatin condenses
Prophase
• 50-60% of mitosis • Chromosomes start to become visible,
– Chromatin condenses • Centrioles separate and go to opposite sides of
the nucleus • Spindle begins to form (helps separate
chromosomes) • Lastly the nucleus disappears and the nuclear
envelope breaks down
Prophase
Metaphase
• 2nd phase, only last a few minutes !
• Chromosomes line up across center of cell !
• Microtubules connect to the centromere of each chromosome
Metaphase
Anaphase• 3rd phase !
• Centromeres that joined the sister chromatids separate !
• Chromosomes separate into 2 groups moving towards the poles !
• Ends when the chromosomes stop moving
Anaphase
Telophase• 4th and final phase of mitosis !
• Chromosomes begin to unravel and disperse !
• Nuclear envelope/membrane begins to reform !
• Spindle breaks apart !
• Daughter cells become visible
Telophase
Cytokinesis
• Cytoplasm pinches in half to create the 2 new daughter cells – Separating the 2 new nuclei !
• Daughter cells now have identical chromosomes
Cytokinesis
Cytokinesis: Animal vs. Plant Cell
Regulating the Cell Cycle
• Not all cells move through the cell cycle at the same rate. !
• External Controls • Proteins respond to events outside of
the cell. • Direct cell to speed up or slow down
cell cycle. • Growth Factors
• Stimulate growth and division of cells !24
Regulating the Cell Cycle
• Not all cells move through the cell cycle at the same rate. !
• Internal Controls • Proteins that respond to events inside the cell.
• Allow cell cycle to proceed only when ready. • Cyclins
• Proteins that regulate the timing of the cell cycle.
• CDK • Binds to cyclins to promote cell cycle
progression.
What Controls the Cell Cycle???
• CDK: always present in cells • Cyclin: level varies throughout the cell cycle • MPF: “mitosis promoting factor” --occurs when
cyclin binds to CDK.
Cancer• Cancer is when the cell cycle
goes wrong. • Body’s cells lose ability to
control growth. • Cancer cells do not respond
to signals that regulate the growth of cells.
• Form masses called tumors.
• Several causes, but common factor is uncontrolled growth.
• p53 gene
Mitosis
Be able to describe and sketch what’s happening:
• Chromosomes • Nuclear Envelope • Spindle
Mitosis Chromosomes Nuclear Envelope
Spindle
DNA coils into c’somes
Begins to disappear
Spindles begin to grow;Centrioles begin to move to opposite poles
C’somes line up along equator
Spindle fibers attach to c’some at centromere
Sister chromatids split -- move to poles
Spindles shorten
C’some have moved to oppostie poles
Begins to reform
Spindle breaks down
Mitosis Animations
• Mitosis Rap !
• Twilight Mitosis !
• Mitosis Animation !
• Mitosis Animation