CHAPTER 20 MITOSIS There is more to lectures than the power point slides! Engage your mind

The Cell Cycle - Mitosis

Where it all began… You started as a cell smaller than a period at the end of a sentence… Going from an egg to a baby…. the original fertilized egg has to divide… and divide…

Rudolf Virchow, 1855, German physician: “ Where a cell exists, there must have been a preexisting cell” The continuity of life is based on the reproduction of cells or “CELL DIVISION”

Cell division process is an integral part of the cell cycle ---- life of a cell from the time it is first formed during division of parent cell until its own division into two daughter cells Most cell division involves distribution of identical genetic material (DNA) to two daughter cells ========== Mitosis *Exception is a process called Meiosis (cell division producing sperm or eggs)

The Cell Cycle © Pearson Education, Inc.

Why do cells divide? Multi-celled organisms o for growth & development  from fertilized egg to adult o for repair & replacement  replace cells that die from normal wear & tear or from injury amoeba

Dividing cells… What has to be copied? o DNA o organelles o cell membrane o lots of other molecules  enzymes animal cell plant cell

Genetic Material DNA molecules are packaged into structures called “Chromosomes” Each eukaryotic chromosome consists of one very long DNA molecule associated with proteins Entire complex of DNA and proteins that is the building material of chromosomes is referred to as “Chromatin”

Nuclei of human somatic cells (all body cells except the reproductive cells) each contain 46 chromosomes, made up of two sets of 23 Each set inherited from each parent

Copying DNA A dividing cell duplicates its DNA o creates 2 copies of all DNA o separates the 2 copies to opposite ends of the cell o splits into 2 daughter cells But the DNA starts as a loosely wound in the nucleus If you tried to divide it like that, it could tangle & break nucleus cell DNA

Organizing & packaging DNA nucleus cell DNA nucleus cell 4 chromosomes in this organism DNA in chromosomes in everyday “working” cell DNA in chromosomes in cell getting ready to divide DNA has been “wound up”

Chromosomes of Human Female 46 chromosomes 23 pairs

Chromosomes of Human Male 46 chromosomes 23 pairs

double-stranded human chromosomes ready for mitosis

Cell Cycle Cell grows in (G1), continues to grow as it copies its chromsomes (S), grows more as it completes preparations for cell division (G2), and divides ( M) Daughter cells may then repeat the cycle

DNA must be duplicated… nucleus cell DNA in chromosomes nucleus cell duplicated chromosomes chromosomes in cell 4 single-stranded chromosomes duplicated chromosomes 4 double-stranded chromosomes

Mitosis: Dividing DNA & cells Stage 1: cell copies DNA nucleus cell DNA Copy DNA! (interphase)

MITOSIS

1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

Mitosis: Dividing DNA & cells Stage 2: DNA winds into chromosomes o keeps it organized nucleus cell duplicated chromosomes like a Plate of spaghetti! (prophase)

Prophase Chromatin fibers become more coiled, chromosomes become observable with light microscope Nucleoli disappear Mitotic spindle starts to form, composed of centrosomes and microtubules

Mitosis: Dividing DNA & cells Stage 3: Chromosomes line up o chromosomes line up in middle o attached to protein “cables” called Spindle Fibers that will help them move duplicated chromosomes lined up in middle of cell Meet in the Middle (metaphase)

Metaphase Chromosomes align along the equator of the cell

Mitosis: Dividing DNA & cells Stage 4: Chromosomes separate o chromosomes split, separating pairs o start moving to opposite ends chromosomes split & move to opposite ends Pull APART (anaphase)

Anaphase Begins when sister chromatids separate at the centromeres and move toward opposite ends of the cell

Mitosis: Dividing DNA & cells Stage 5: Cell starts to divide o cells start to divide o nucleus forms again Two Cells! (telophase)

Telophase Nuclear membrane forms around the two new daughter nuclei Nucleoli reappear Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete

Mitosis: Dividing DNA & cells Stage 6: DNA unwinds again o cells separate o now they can do their every day jobs (cytokinesis)

Cytokinesis Formation of cleavage furrow, pinching the cell into two Cytoplasm of parent cell divides into two daughter cells

New “daughter” cells Get 2 exact copies of original cells

Overview of mitosis interphaseprophase metaphaseanaphasetelophase cytokinesis I.P.M.A.T.C. P lease M ake A nother T wo C ells