Mitosis--Cell Copying

Bio 100

Tri-County Technical College

Pendleton, S. C.

Ye ole cell division

• Cell division simply means one cell dividing to become two cells

• Process can have varied purposes and results

• 1. Can be a form of reproduction• 2. Replacement of lost or damaged cells• 3. Growth and maturation• 4. Production of special types of cells

Let me answer this one, Doc!

• Asexual reproduction DOES NOT INVOLVE the formation of gametes (sex cells)

• Sexual reproduction DOES involve the formation of gametes

• How those gametes are gotten together is another story and can be a real hoot!

DNA in varied forms…

• In eukaryotes, the DNA (genetic material) of a nondividing cell occurs in string-like, unwound form called CHROMATIN

• Prior to cell division, the chromatin condenses and super-condenses into chromosomes

• Only difference between chromatin and chromosomes is their FORM (arrangement)

Let me see that again

Chalk talk time on the composition of an eukaryotic chromosome

It is composed of two SISTER CHROMATIDS joined at location known as CENTROMERE

Unless mutation occurred, each contains the same genetic material (copies of each other)

Intro to Mitosis and Meiosis

• Mitosis and meiosis are terms that describe “nuclear” division

• Terms apply to eukaryotic cells

• Most prokaryotes utilize binary fission (fission) for “reproduction”

• Term simply means “splitting in two”

• Copies genetic material and “splits” forming two cells that are “clones” of “parent” cell

The Cell Cycle

• The life of a cell can be described with the cell cycle.

• After going through the cycle a set number of times, a cell dies.

• Mitosis is a part of the cycle.

Phases of Cell Cycle

• G-1– first gap phase after mitosis is finished– DNA components are synthesized

• Synthesis Phase– DNA is replicated– chromosomes are replicated

• G-2– gap phase after DNA replication

Mitosis

• G-1, Synthesis Phase, and G-2 were considered to be a part of mitosis known as Interphase

• Interphase– period of time for Gap-1, S, and Gap-2 phases– nucleus is not dividing– cell is getting ready to divide

Prophase

• The chromosomes are replicated by this time and become visible.

• The nuclear membrane disappears.

• Duplicate chromatids attached at the centromere

• Centrioles duplicate and move to opposite poles of the cell.

More on Prophase

• Microtubules are organized into a spindle

– used to move chromosomes

• Nuclear membrane disappears

• Chromatids become attached to the spindle fibers at their centromeres

Chromo- somes and -tids

Prophase

Metaphase

• Duplicated chromosomes line up single file in the middle of the cell between the two centromeres.

Anaphase

• The chromatids are separated and pulled to opposite ends of the dividing cell by the spindle fibers.

• “Ana-” means split

Telophase

• Back to interphase• nuclear membrane

reforms around each set of chromomes

• cytoplasm is split between the new cells

• chromosomes disappear

The End Result

• Two cells with the same chromosome number and genes as the original cell.

• How is genetic information preserved?– Accurate DNA replication due to accurate base

pairing

• Both cells go into the Gap-1 phase after telophase.

Cytokinesis

• Mitosis designed to parcel genetic material• When completed, two identical nuclei in

one cell (excluding any mutation, of course)• Cytokinesis needed to divide the cytoplasm

and organelles• Plant cell cytokinesis utilizes formation of

cell plate which will become cell wall• Animal cell cytokinesis utilizes “cleavage

furrow” for producing daughter cells• Wonder where they got that name?

To test your understanding of mitosis, sketch a cell with four chromosomes: one short dark, one short light, one long light, and one long dark and then carry the nucleus of the cell through mitosis.

Works so well…but

• A tumor is produced by mitosis gone amuck

• Something happens to the controls that regulate orderly cell division

• Benign tumor will not spread throughout body but can still be very dangerous

• Malignant tumor WILL spread to other locations by METASTASIS

• According to the statistics…will touch every family in US at one time or another

Naming cancers…• Named according to where they originate• Carcinomas originate in external/internal

coverings of the body• Sarcomas arise in tissues that support the body

(bone/muscle)• Leukemias and lymphomas are cancers of blood

forming tissues such as bone marrow and lymph nodes

• Treatments: surgery, radiation, chemotherapy, holistic, and charlatans