Unit 4 Cell Cycle & Mitosis

Cell reproduction in multicellular and unicellular organisms Unicellular: reproduce by binary fission, asexual reproduction Multicellular: reproduce by cell division; process of growth and repair depend on cell division; also involves the production of sex cells

Describe chromosomes Carriers of genetic material found in nucleus Made up of DNA Information is copied and passed to future generations Usually DNA exists as chromatin which are long, winding strands that condense into chromosomes before dividing Animation: http://www.johnkyrk.com/chromosomestructure.html

Chromosome structure Chromosomes are made up of two chromatids which are held together with a centromere Human chromosome number is 46 in body cells (somatic cells); 23 in sex cells (gametes)

Describe the cell cycle Sequence of growth and division in the cell Consists of 4 phases: 1. G1 phase: growth phase 2. S phase: copying of chromosomes (DNA replication) 3. G2 phase: growth phase 4. M phase: cell division Interphase is the growth period where DNA is copied; includes G1, S, and G2 Mitosis: dividing period producing two new cells; happens in M phase Cytokinesis=division of cytoplasm

List and describe the steps of mitosis Mitosis is the division of the cells (the nucleus, followed by cytokinesis) producing two cells with the same number of chromosomes

Prophase Longest phase of mitosis Chromatin coils into chromosomes The nucleus disappears Centrioles form and move to opposite poles of cell Spindle fibers form from centrioles and begins to cross cell

Metaphase Chromosomes line up in the middle of the cell Spindle now forms across the cell

Anaphase Spindle fibers begin to shorten This pulls chromosomes apart Now the chromosome halves are referred to as chromatids

Telophase Chromatids reach poles Chromosomes unwind into chromatin Spindle fibers break down Nucleolus and nuclei reform Plasma membrane begins to pinch in

Cytokinesis Division of cytoplasm In animal cells: cell membrane continues to pinch in until two cells are formed In plant cells: cell plate forms in center of cell and eventually splits cells At the end of mitosis, two new cells are produced; called “daughter” cells Animation: http://www.johnkyrk.com/mitosis.html