The Cell Cycle

The Cell Cycle The cell cycle is the repeated pattern of GROWTH and DIVISION that occurs in eukaryotic cells. There are three parts of the cell cycle: 1. INTERPHASE – cell growth & copying DNA 2. MITOSIS – division of the nucleus 3. CYTOKINESIS – division of the cytoplasm Cells spend about the majority of their time in INTERPHASE

Interphase Interphase is divided into 3 phases: G1 (Gap 1): the cell GROWS and makes PROTEINS S (Synthesis): the chromosomes REPLICATE (x2); form identical sister chromatids held together by a centromere G2 (Gap 2): the cell continues to grow, produce proteins for cell division and PREPARES for cell division

Interphase

CHROMATIN vs. CHROMOSOME During interphase, the cell’s genetic material is visible as a stringy material called CHROMATIN During PROPHASE, the chromatin condenses and supercoils into CHROMOSOMES A chromosome consists of two identical SISTER CHROMATIDS held together by a CENTROMERE.

Sister chromatid centromere chromosome DNA double helix

Mitosis Mitosis begins with one cell, and produces two identical “DAUGHTER CELLS” that have the SAME DNA as the parent cell For example, a normal human skin cell has _____ chromosomes. If the skin cell undergoes mitosis, the result will be TWO new skin cells, each with _____ chromosomes. 46 46

Mitosis 4 strands (2 sister chromatids) break apart so each new cell has one double stranded chromosome. Mitosis follows interphase and is divided into 4 phases

Mitosis Mitosis consists of four phases: (PMAT) Prophase Metaphase Anaphase Telophase

Mitosis

Prophase The CHROMATIN CONDENSES into visible chromosomes The nuclear envelope DISAPPEARS The CENTRIOLES SEPARATE and move to opposite ends of the cell SPINDLE FIBERS FORM and spread out across the center of the cell

PROPHASE

Metaphase Chromosomes LINE UP ACROSS THE MIDDLE of the cell Spindle fibers connect the CENTROMERE of each chromosome to the POLES (Shortest phase of mitosis)

metaPHASE

Anaphase Centromeres that join the sister chromatids split The CHROMATIDS SEPARATE Separated chromatids move to OPPOSITE ENDS of the cell

anaPHASE

Telophase The CHROMOSOMES UNCOIL and become chromatin once again The Nuclear Envelope REFORMS around the chromatin at each end of the cell Spindle fibers DISSOLVE CYTOKINESIS begins

teloPHASE

Cytokinesis Cytokinesis is the DIVISON OF THE CYTOPLASM IN PLANTS IN ANIMALS a CLEAVAGE FURROW forms and the cell membrane “pinches” inward between the two nuclei IN PLANTS The cell cannot “pinch” inward because of the cell wall, so a CELL PLATE forms between the two nuclei

Cytokinesis in animal cells

Cytokinesis in plant cells Cell plate