mitosis part 1
TRANSCRIPT
Mitosis
• Why do cells need to divide?
Recap…
• Cell theory…– Cells are the basic structural unit of life– Cells are the functional units of life– Cells come from pre-existing cells
Overview• Why do cells need to divide?– Repair, growth, development
• Types of reproduction– Sexual
• Genetically different• 2 parents• Takes time to develop, better chance of survival
– asexual• Genetically identical• One parent• Many offspring very quickly
DNA• Blueprint of life, nucleic acid• Chromatin– Granular genetic material, spread out in nucleus of
non-dividing cells• Chromosomes– Condensed genetic material, in dividing cells
• Sister chromatids– Identical copies of Chromosomes joined by a
centromere (“centro-” middle)
Humans• 46 chromosomes – 46 sister chromatids– One from your mom, one from your dad
Cell Cycle: Life of a Cell
Cell Cycle• Interphase– 90 % of cell’s life, non dividing– G1 phase
• Grows, makes organelles
– S phase• DNA Synthesis…DNA replicates
– G2 phase• Cell prepares to divide, makes sure it has all important organelles for
division
• M phase– When the cytoplasm and nucleus of the cell divides
Cell Cycle
• There are check points in G1, S, and G2– Make sure cell is ready to move onto the next
phase (has all necessary organelles, copied DNA, etc.)
• Once the cell has past the G1 checkpoint, it will complete the cell cycle
• Some cells stay in the G1 phase all their life (muscle cell, brain cells)
Regulators of Cell Cycle• Cyclins– Protein that regulates the timing of the cell cycle
in eukaryotic cells– Levels of cyclins rise and fall throughout the cell
cycle• Cyclin-dependent Kinases (cdks)– Enzymes that are activated when they bind with
cyclin and they make the cell cycle continue
Regulators• Internal– Factors within the cell that control cell cycle– Cyclin and CDKs• Allow cell cycle to proceed only when certain processes have
occurred– Replication of chromosomes– Chromosome Attachment to spindle before anaphase
• External– Factors Outside the cell• Growth factorsmolecules that bind to cell surface that signal
cell to divide• Similar cells have molecules that have opposite effect so that
when it becomes to crowded, cells stop dividing
M-phase• Consists of mitosis and
cytokinesis• Mitosis– Process by which the nucleus
of a cell divides– One parent cell makes two
identical daughter cells– This is how organisms repair
tissue and grow and develop• Cytokinesis-division of the
cytoplasm
Depending on cell type…
• Mitosis can take a few minutes or a few days• Muscle cells (non-dividing)• Nerve cells (non-dividing)• Skin cells (divide all the time)• Digestive Tract cells (divide all the time)
Life Span of Some Human Cells
Cell type Life span Cell division
Lining of esophagus 2-3 days Can divide
Lining of small intestine 1-2 days Can divide
Lining of the large intestine
6 days Can divide
Red blood cells Less than 120 days Cannot divide
White blood cells 10 hours to decades Many do not divide
Smooth muscle Long-lived Can divide
Cardiac (heart) muscle Long-lived Cannot divide
Skeletal muscle Long-lived Cannot divide
Neurons (nerve) cells Long-lived Most do not divide
Easy way to remember M-Phase
• PMAT • Pilates Make Annie Toned• Practice Makes Athletes Train
– Prophase– Metaphase– Anaphase– Telophase
Prophase• 50-60% of time• Chromosomes become visible• Centrioles develop in cytoplasm near nuclear envelope• Centrioles separate and migrate to opposite ends of
nuc. Env.• Centrosome– Region where Centrioles are found– Organize the “spindle”
• Fan like microtubule structure that helps separate chromosomes
• Plants do NOT have Centrioles
End of prophase
• Chromosomes coil together tightly• Nucleolus disappears• Nuclear envelope breaks down
Metaphase
• Few minutes• Chromosomes line up in middle (M in
metaphase MIDDLE)• Microtubules connect centromere of each
chromosome to the 2 poles of spindle
Anaphase
• Centromeres joining sister chromatids separate and become individual chromosomes
• They are dragged by fibers to opposite poles• Ends when chromosomes stop moving
Telophase
• Opposite of prophase• Condensed chromosomes disperse into tangle
of material• Nuclear envelope reforms• Spindle breaks apart• Nucleolus becomes visible• At the end 2 identical nuclei in one cell
Cytokinesis
• Happens at the same time as Telophase• Division of cytoplasm• Animal Cells– Cell membrane drawn inward until it pinches off
and forms 2 id daughter cells• Plant Cells– Cell plate forms between nuclei– Cell Plate develops into separate membrane – Cell wall appears
Regulators of Cell Cycle• Cyclins– Protein that regulates the timing of the cell cycle
in eukaryotic cells– Levels of cyclins rise and fall throughout the cell
cycle• Cyclin-dependent Kinases (cdks)– Enzymes that are activated when they bind with
cyclin and they make the cell cycle continue
Regulators• Internal– Factors within the cell that control cell cycle– Cyclin and CDKs• Allow cell cycle to proceed only when certain processes have
occurred– Replication of chromosomes– Chromosome Attachment to spindle before anaphase
• External– Factors Outside the cell• Growth factorsmolecules that bind to cell surface that signal
cell to divide• Similar cells have molecules that have opposite effect so that
when it becomes to crowded, cells stop dividing