why do cells need to divide?
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Why do cells need to divide?. How do cells divide? What needs to happen to make an exact copy of this cell? . Does an organism grow because its cells get larger or because it increases the number of cells? What limits the size that a cell can reach? - PowerPoint PPT PresentationTRANSCRIPT
Why do cells need to divide?
How do cells divide? What needs to happen to make an exact copy of this cell?
• Does an organism grow because its cells get larger or because it increases the number of cells?
• What limits the size that a cell can reach?• How does the surface area change when a large cell
divides into smaller cells that have the same total volume?
• Are cells dividing all the time?• Do all cells divide at the same rate?• What must duplicate/replicate before a cell divides?
Types of Reproduction
• Asexual Reproduction
– Cloning of an individual cell
– Produce genetically identical offspring
– Occurs in bacteria, body cells
• Sexual Reproduction– Occurs when two
reproductive cells join– Make genetically diverse
cells since the offspring get traits from both parents
VocabularyChromatin- long strand of
DNAChromatid- each strand of a
duplicated chromosomeCentromere- the area where
two chromatids are joined. Splits during anaphase.
Kinetochore- a protein on chromosomes where spindle fibers attach.
Centrioles- tiny structures in the cytoplasm of animal cells that help organize the spindles. (2 centrioles =centrosome)
Spindle fiber- a fanlike microtubule structure that helps separate the chromatids
• Spindle- a fanlike microtubule structure that helps separate the chromatids -composed of centrioles and spindle fibers
Cell Cycle- Interphase• G1 – Cell Growth-increase in
size, routine functions (longest)
• S – DNA replication- Synthesis of new DNA/ chromosomes replicated
• G2- Preparing for Cell Division- replication of organelles, microtubules and other molecules for cell division
• http://iknow.net/cell_div_education.html
M Phase (minutes to days)
• Mitosis– Prophase– Metaphase– Anaphase– Telophase
Pro=beforeMeta=afterAna=backTelo= end
• Cytokinesis– Division of the
cytoplasm and organelles
Mitosis- phases
• Prophase– Chromosomes become
visible (coil)– nuclear membrane
dissolves – Spindle forms– Nucleolus disappears
Prophase
Metaphase
• Chromosomes line up along the equator
• Spindle fibers connect centromeres (of chromatids) to opposite poles
Anaphase
• Centromeres divide• Chromosomes move
toward opposite poles– Each Sr. Chromatid is
pulled toward opposite pole
• Spindle fibers shorten
Telophase
• Reverse of Prophase• Nuclear membrane
forms at each pole• Chromosomes uncoil• Spindle fibers dissolve• Cytokinesis begins
Cytokinesis
• Cytoplasm divided in half
• Cell membrane pinched by a belt of protein threads or contractile ring
Plant vs Animal Cell Division
Animals• Centrioles• Pinching or cleavage of cell
membrane
BothEqual sized offspring cellsIdentical copy of original cell’s
chromosomes
Plants• No centrioles• Vesicles fuse forming a cell
plate• A new cell wall forms on
either side of the cell plate
Animal and Plant Cell Division
• http://iknow.net/cell_div_education.html
• Prophase- a “pro” is #1• Metaphase- “M” middle• Anaphase- Away• Telephase – Two nuclei
• http://glencoe.mcgraw-hill.com/sites/dl/free/0078802849/164155/00053413.html