MITOSIS 10/8/10

James
Unit 2 - CELLS
MITOSIS = cell division
Scribe Post for Friday, 10/8/10

Cells divide to replace damaged cells, reproduce organisms, to grow, to transfer genes from cell to cell, and for a unicellular organism to become multicellular

TYPES OF REPRODUCTION
Sexual (MEIOSIS)- fertilization of an egg by sperm (each contain half of the parent cell's chromosomes), occurs in reproductive organs (ovaries/testes)

Asexual (MITOSIS)- no fertilization at all, parent and offspring have the same genes, binary fission (organism splits into 2, found in single celled organisms)

Chromosomes

-Contain almost all genes of a eukaryotic cell
-Visible with light microscope during cell division
-Chromatin (invisible) are masses of long thin fibers, contain DNA/protein
-Before cell division, chromatin coils up to form chromosomes
-Humans have 46 chromosomes (varies by species)
-Each chromosome can have over 1,000 genes

Chromosome Replication

-Genetic material must be doubled before cell division to make sure that the daughter cells match the parent cell
--Sister chromatids are identical copies of each other connected at the centromere
--Daughter cells are the result of cell division, DOES NOT IMPLY GENDER

The Cell Cycle

Interphase (Pre-Mitosis) - 90% of cell cycle
-GI (Gap 1) - cell grows 2x bigger, protein synthesis, more organelles, 2x cytoplasm
-S (Synthesis) - chromosome replication (in nucleus)
-G2 (Gap 2) - Final preparation before division



Prophase - CHROMOSOMES AND SPINDLE FIBERS COME, NUCLEAR ENVELOPE GOES!
-Chromosomes coil/condense to become visible
-Nucleoli disappears
-Sister chromatids connected at centromere
-Spindle forms

-Nuclear envelope breaks down
-Spindle attaches to centromeres and move chromosomes to center of cell

Metaphase - DUPLICATED CHROMOSOMES CENTER UP!
-Spindle completely formed
-Centromeres on chromosomes are lined up on equator between the poles
-Spindle is attached to each sister chromatid, pushes chromosomes to center

Anaphase - DUPLICATED CHROMOSOMES SEPARATE AND MIGRATE!

-Sister chromatids are separated and each are now known as daughter chromosomes
-Motor proteins on centromeres move chromosomes toward opposite pole of cell
-Spindle attached to chromosomes shorten
-Spindle not attached to chromosomes lengthen to extend cell and force poles further apart to prepare for daughter cells

Telophase - NUCLEAR MEMBRANE FORMS AROUND NEW CHROMOSOMES!

-Begins once chromosomes reach poles
-Opposite of Prophase
--Nuclear envelope REAPPEARS
--Nucleoli REAPPEAR
--Chromosomes UNCOIL
--Spindle DISAPPEARS
--MITOSIS IS NOW FINISHED

Cytokinesis - CYTOPLASM DIVIDES TO FORM 2 DAUGHTER CELLS!

-Begins during telophase
-'CLEAVAGE' in animal cells
-cleavage = indent at equator of cell that pinches cell in 2
-Formed by ring of microfilaments inside cell membrane
-In plant cells, cell plate forms by starting in center of cell and moving outward to bisect cell

Cell Cycle Control

-Cells that are not directed by the cell cycle divide out of control
-Result is a benign tumor (abnormal mass of normal cells)
--can cause problems depending on location
--as it grows, displaces normal tissue

Cancer

-Cancer cells have faulty cell cycle, divide out of control
-Malignant tumor = lump that results from division of cancer cell
-Metastasis = spreading of cancer cells to other organs
-Cancer is named for where they begin
--Carcinomas - originate in external/internal coverings of body
--Sarcomas - originate in tissues that support body
--Leukemia - cancer of blood forming tissue (bone marrow)
--Lymphomas - cancer of blood forming tissue (lymph nodes)

Cancer Treatments

Radiation Therapy

-Cancer cells exposed to high-energy radiation disrupt cell division
-Radiation destroys cancer cells without harming normal cells
-Bad side effects (sterility)

Chemotherapy

-Drugs that disrupt cell division
-Antimitotic drugs - prevent cell division by interfering with spindle formation

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