Somatic Cell Division Mitosis

Somatic Cells All body cells except gametes (sex cells)

Somatic Cell Division A cell divides into two identical cells Replaces dead or injured cells Adds new cells for tissue growth

DNA Replication (Duplication) The DNA sequences that make up the chromosomes have to be copied so the same genetic material can be passed on to the new cells

Cell Cycle The sequence of changes a cell undergoes from the time it forms until the time it duplicates its contents and divides into 2 cells Two major time periods: Interphase – not dividing Mitotic Phase - dividing

Interphase The cell replicates DNA and manufactures additional cell organelles and cytosolic components High metabolic activity Most growth

DNA Replication DNA nucleotides are synthesized in the cytosol and imported to the nucleus The helical DNA uncoils and the 2 strands separate between the base pairs The exposed base pair on each strand pairs with a newly synthesized complementary nucleotide The new DNA strands take shape as chemical bonds form

DNA Replication - continued The original DNA molecule has become 2 identical strands of DNA Once a cell completes DNA replication, the mitotic phase can begin.

Mitotic Phase Mitosis – division of the nucleus Cytokinesis – division of the cytoplasm

Nuclear Division The duplicated chromosomes become divided such that one set ends up in each nucleus The process is divided into 4 stages: Prophase, Metaphase, Anaphase and Telophase **Mitosis is a continuous process and one phase merges with the next**

Prophase Chromatin fibers condense and shorten into chromosomes Each prophase chromosome consists of a pair of identical double stranded chromatids Mitotic Spindle is formed by the pericentriolar material and centrioles are pushed to opposite sides of the cell The nucleolus and nuclear envelope break down

Metaphase The centromeres of the chromatid pairs are aligned along the center of the mitotic spindle – this is called the metaphase plate

Anaphase The centromeres split, separating the chromatid pair, which move to opposite ends of the cell. Once separated the chromatids are called chomosomes.

Telophase Final stage of mitosis Begins when chromosome movement stops The chromosomes start to uncoil, a new nuclear envelope forms, nucleoli appear and the mitotic spindle breaks up. TWO nuclei are present and the cell starts to divide into 2

Cytoplasmic Division - cytokinesis Division of the cell’s cytosol and organelles Begins in late anaphase/early telophase with the formation of a cleavage furrow Cleavage Furrow – slight indentation of the plasma membrane

Checkpoint What is the difference between a chromatid and a chromosome? In which stage of the cell cycle is the cell growing? What are the mitotic phases in order? What is a major event in each stage?