Mitosis

Why do cells divide? (Purpose of Mitosis) Growth Repair and replace dead cells asexual reproduction

What cells divide often? Skin Stomach lining Red Blood cells Embryo Plant roots Hair Nails

What cells rarely/never divide? Nervous System (nerve cells) Liver (liver cells)

Interesting Fact: Why do we age? Eventually cells stop being replaced “Apoptosis” –Cell death “We die because our cells die.” –William R. Clark

“C” Terms Chromosomes –Long threads of genetic material –Found in nucleus Chromatid –One side of a duplicated chromosome

“C” Terms Centromere –Structures that hold sister chromatids together NOTE –2 sister chromatids = 1 duplicated chromosome

DNA is broken into long strands and wrapped around proteins to form structures called chromosomes.

“C” Terms… Centrioles –Small protein bodies –In cytoplasm –Animal cells only –Spindle fibres extend from centrioles.

Micrograph of a Chromosome

Cell Reproduction Cells must divide to increase the number of body cells (not egg or sperm) in an organism There are two parts to it: –mitosis - the division of the nuclear material –cytokinesis - the division of the cytoplasm and organelles

Cell Division in a Nutshell Before: –Chromosome duplicates = 2 sister chromatids (DNA replication ) During: –Sister chromatids separate After: –2 “daughter” cells –Genetically identical

Mitosis Phases Interphase Prophase Metaphase Anaphase Telophase

Stages of Mitosis: Interphase resting phase (period between divisions) centrioles are just outside the nuclear membrane nucleolus is present and DNA appears as fine threads called chromatin DNA replicates and appears as double chromosomes and centrioles begin to move apart near the end of this phase

Interphase membrane

Stages of Mitosis: Prophase nucleolus disappears centrioles move to opposite sides of nucleus asters and spindle fibers form around each centriole nuclear membrane disappears chromosomes are visible as two sister chromatids held together at the centromere

Prophase Spindle fiber membrane

Stages of Mitosis: Metaphase chromosomes line up along equator (middle) of cell spindle fibers extend from centrioles (poles) to centromeres of the paired chromatids

Metaphase

Stages of Mitosis: Anaphase chromatids separate and move toward opposite poles

Anaphase

Stages of Mitosis: Telophase chromosomes disappear; chromatin reappears spindle fibers and asters disappear nucleolus reappears and nuclear membrane reforms cell membrane pinches inward to split cytoplasm (cytokinesis)

Telophase & Cytokinesis

Cytokinesis…

Concept Map

Mitosis Animation

Mitosis in Plants Mitosis in plants is very similar to animals with 2 exceptions: –plant cells lack centrioles –plant cells form a cell plate between the two daughter cells in telophase.

Cytokinesis in Plants

Cytokinesis Why would it occur differently in animal and plant cells? Plant cells have a rigid cell wall!

Cytokinesis Animal Cells Plant Cells Cell membrane pinches inward Creates cleavage furrow Think: –Pull a string around a balloon Cell Plate forms between two new nuclei Becomes cell wall

What phases do you see? A D B C

What phase? Interphase

What phase? Prophase

What phase? Metaphase

What phase? Anaphase

What phase? Telophase

What phase? Interphase

Understanding Concepts 1)Go to page 90 in BIOLOGY 11 BOOK - Answer questions 2, 3, 4, 5, 6, 7, 9, 10 2) Complete Mitosis Review Worksheet