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

Vocabulary Chromatin- long strand of DNA Chromatid- each strand of a duplicated chromosome Centromere- 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 G 1 – Cell Growth-increase in size, routine functions (longest) S – DNA replication- Synthesis of new DNA/ chromosomes replicated G 2 - Preparing for Cell Division- replication of organelles, microtubules and other molecules for cell division

M Phase (minutes to days) Mitosis – Prophase – Metaphase – Anaphase – Telophase Pro=before Meta=after Ana=back Telo= 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 Both Equal sized offspring cells Identical 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

Prophase- a “pro” is #1 Metaphase- “M” middle Anaphase- Away Telephase – Two nuclei

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