Mitosis and the Cell Cycle

Unicellular organisms

Reproduces the entire organism

Multicellular Organisms

Develop from a fertilized egg, grow, repair

Cellular Organization of the Genetic Material

Genome : All the DNA in a cell - prokaryotes have single DNA molecules / eukaryotes have multiple DNA molecules

DNA molecules in a cell are packaged into chromosomes

Somatic cells : Body cells that have 2 sets of chromosomes, 46 total, 23 pairs

Gametes : Reproductive cells, half as many chromosomes as somatic cells

Distribution of Chromosomes During Eukaryotic Cell Division

DNA is replicated and chromosomes condensed

Each duplicated chromosome has 2 sister chromatids, which separate during cell division

Centromere is the “waist” of the duplicated chromosomes where chromatids are attached

Phases of the Cell Cycle

Interphase, Mitosis / Meiosis, Cytokinesis

Interphase

Period of regular cell activity

DNA is uncondensed thread-like chromatin

DNA is copied if cell is going to divide (In S phase)

Has 3 phases of G₁, S , G₂

Prophase

Nuclear membrane breaks apart

DNA condenses into chromosomes

2 chromosome ‘arms’ are called sister chromatids - attached by a centromere

Centrioles move to opposite ends and form spindle fibers

Spindle fibers attach to chromosomes and pull at centromere

Metaphase

Chromosomes line up along the middle of the cell

Anaphase

Spindle fibers separate chromatids

At end of anaphase, one complete set of chromosomes gathers at each pole of the cell

Telophase

Chromosomes uncoil into chromatins

Nuclear membrane reforms around chromosomes

Cytokinesis

Cell membrane pinches in and for plants a plate is formed. The pinch is called “cleavage furrow'“

Two identical daughter cells are formed

Regulation of Cell Cycle

Regulated by molecular control system

Frequency of cell division varies with the type of cell

Cell cycle differences result from regulation at the molecular level

Loss of Cell Cycle Controls in Cancer Cells

Uncontrolled cell division and do not communicate to other cells - how they spread

Causes : Genetics, Mutagens

Cancer cells form tumors

Abnormal cells remain at original site, lump is called a benign tumor

Malignant tumor invade surrounding tissues can metastisize