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