CELL CYCLE Mitosis

DNA The cells genetic information is carried by the chromosomes which are formed by proteins and DNA. The cells of all organisms have a specific number of chromosomes, for example: Fruit flys have 8 chromosomes Humans have 46 chromosomes

DNA (cont.) In order for the DNA to fit inside the nucleus, it must compact itself by coiling When DNA is unwound, it is in long, thin strands called chromatin When the DNA is completely compacted it is in the form of chromosomes and becomes visible under a microscope

Chromosomes Before cellular division, each chromosome replicates Each chromosome is made up of two identical sister chromatids joined by a centromere When the cell divdes, the sister chromatids separate and each one passes into one of the two new cells

Cell Cycle Period from the beginning of one cell division to the beginning of the next cell division Divided into 2 parts: Interphase Cell Division

Cell Cycle Cell Cycle Interphase Cell Division

Interphase Occurs between cell divisions Cell prepares all the materials necessary for cell growth and prepares it for division Accounts for 90% of the total time in the cell cycle Divided into 3 stages: G1 S G2

Cell Cycle Cell Cycle Interphase Cell Division G1

G1 Also known as Gap 1 Characterized by growth and development

Cell Cycle Cell Cycle Interphase Cell Division G1 S

S Also known as the synthesis phase Once the cell enters the S phase it is committed to cell division Chromosomes in the nucleus replicate

Cell Cycle Cell Cycle Interphase Cell Division G1 S G2

G2 Also known as Gap 2 This is the shortest of the 3 phases in interphase Cell makes organelles and other materials Centrioles replicate to form 2 pairs

Cell Division Splitting of one cell to form 2 cells Divided into 2 parts: Mitosis Cytokinesis

Cell Cycle Cell Cycle Interphase Cell Division G1 S G2 Mitosis Cytokinesis G1 S G2

Mitosis Process during which a cell’s nucleus divides into two identical nuclei It is divided into 4 phases: Prophase Metaphase Anaphase Telophase

Cell Cycle Cell Cycle Interphase Cell Division G1 S G2 Mitosis Cytokinesis G1 S G2 Prophase Metaphase Anaphase Telophase

Prophase Cromatin condenses Proteins form microtubules which form a fibrous structure called the mitotic spindle Spindle stretches out between opposite poles of the cell Nuclear envelope and nucleolus break down Centromere attaches to spindle fibers Fibers move chromatids to center of cell

Metaphase Chromosomes are pulled to center of cell Chromosomes line up on an imaginary line called the metaphase plate ALIGNMENT IS CRUCIAL TO ENSURE THAT EACH CELL GETS A COMPLETE SET OF CHROMOSOMES

Anaphase Centromeres divide Spindle fibers pull chromatids toward opposite poles Ends when chromosomes are at opposite ends of the cell

Telophase 2 daughter nuclei form Nuclear envelopes form around each set of chromosomes Nucleoli appear Chromosomes uncoil to form chromatin Mitotic spindle disassembles

Cytokinesis Process in which the cell’s cytoplasm divides to make 2 daughter cells Each daughter forms around 1 of the 2 nuclei produced during mitosis Begins during telophase

Cytokinesis in Animal Cells The cell membrane, at the center of the cell, folds inward to form a cleavage furrow The cell continues to pinch in half at the furrow until the membrane meets and forms a division resulting in 2 cells with complete cell membranes

Cytokinesis in Plant Cells In plant cells, a cell plate forms between the two new nuclei and then a cell wall forms around it