Friday in Biology Get out journal Pick up scissors and glue First page of Journal ____your names __________ Biology Journal Biology Wikipage THE CELL CYCLE and Mitosis: Cells at Work!! Review: DNA & Chromosomes DNA the molecule that carries the genetic information Ex. The toilet paper Gene a section of DNA that codes for a protein/trait Ex. A small piece of toilet paper Histone Proteins that the DNA wraps around to form chromosomes Ex. The toilet paper roll Chromosome a long DNA molecule found in the nucleus Ex. The toilet paper on the toilet paper roll Chromosome Structure Sister chromatids duplicated chromosomes that are attached to each other Centromere narrow waist where sister chromatids are attached Chromosome Structure Telomeres ends of chromosomes that protect DNA from damage (hard hats) Kinetochores disc-shaped proteins that attach chromosomes to the spindle (handles) Chromosomes vs. Chromatin Chromosomes -Toilet paper on the toilet paper rolls -Organized for distribution (information cannot be used) -Mitosis Chromatin -large pile of toilet paper unwound off the roll -information in DNA can be used by cell -Interphase What is the cell cycle? Continuous sequence of growth and division of a cell. 2 parts: Interphase & Mitosis Busiest and longest section is INTERPHASE After DNA is replicated (during Interphase), mitosis can begin Cell Cycle Interphase: first phase of Cell Cycle G 1 phase cell grows, makes proteins and other products, and does its cell business S phase synthesis phase, when chromosomes (DNA and histone proteins) are replicated G 2 phase cell prepares for division Centrosomes and centrioles replicate Proteins associated with division accumulate Cell Cycle Mitotic Phase Mitosis division of the nucleus and the chromosom es within it Cytokinesis division of the cytoplasm What is Mitosis?? Part of the cell cycle Nuclear cell division during which chromosomes are equally distributed to the 2 identical daughter cells that are formed Results in growth Continuous process 4 stages Stage 1: Prophase Chromatin coils up into chromosomes Nucleus begins to disappear Centrioles migrate to opposite ends of cells and spindle forms Stage 2: Metaphase Chromosomes attach to spindle fibers Chromosomes line up along the equator of the spindle Very short phase Stage 3: Anaphase sister chromatids separate Centromeres split apart Chromatids are pulled to opposite poles of the cell Stage 4: Telophase chromatids reach the poles Chromosomes unwind and spindle breaks down New nuclei form around each set of chromosomes Plasma membrane separates Cytokinesis: Division of the cytoplasm Animal cell Plasma membrane pinches along equator Forms a cleavage furrow that deepens until the cell is pinched in two Plant cell Plasma membrane does not pinch in b/c of rigid cell wall Cell plate forms at the equator that divides the cytoplasm I Pour Milk And Tea IInterphase The Xerox phase PProphase Cell PREPARES and chromosomes become visible MMetaphase The chromosomes line up in the MIDDLE AAnaphase The chromosomes pull APART TTelophase The TWO identical daughter cells separate Purpose of Mitosis (Cell Division) DNA makes an exact copy of itself so that AFTER mitosis, the 2 new daughter cells will be identical. The process of mitosis ensures that each new cell receives the correct number of chromosomes for that organism (Humans = 46 chromosomes) 23 from mom, 23 from dad When both sets of chromosomes are in a cell, it is said to be diploid. All somatic (body) cells are diploid. Cell Cycle Regulation Internal check points External cues Cyclin and kinases (proteins) that are made during G 2 phase Cancer Cancer cells do not respond to cell cycle signals they divide continuously divide or they stop and start dividing at random places in the cell cycle