Bell Ringer 1.Why do cells need to divide in multicellular organisms? 2.What is the difference between prokaryotes and eukaryotes with regard to chromosomes? 3.What does a human chromosome consist of? Draw one! Label. 4.Describe a role of chromatin in chromosome in your own words. DNA and Chromosomes Chromatin Histones DN A The function of chromatin is to efficiently package DNA Cell Cycle Cell Cycle is a sequence of events through which a cell progresses during its lifetime Cell can be either in dividing (Mitotic Phase) or non-dividing state (Interphase) Interphase about 90% of the cell cycle G1 Phase (Gap 1): Cell Growth Protein Synthesis Cell Metabolism Preparation for S Phase S Phase (synthesis): DNA is replicated G2 Phase (Gap 2): Further Cell Growth Protein Synthesis Specialized proteins needed for Cell Division The cell grows during all three phases, but chromosomes are duplicated only during the S phase Mitotic Phase Mitosis: Prophase Metaphase Anaphase Telophase Cytokinesis is division of cytoplasm/cell: cleavage furrow forms in animal cells cell plate (cell wall) forms in plant cells daughter cells are identical Figure 12.10a (a) Cleavage of an animal cell (SEM) Cleavage furrow Contractile ring of microfilaments Daughter cells 100 m Figure 12.10b (b) Cell plate formation in a plant cell (TEM) Vesicles forming cell plate Wall of parent cell Cell plate New cell wall Daughter cells 1 m Cell Cycle Interphase Prophase Metaphase Anaphase Telophase & Cytokinesis Interphase Animal Cell Plant Cell Photographs from: Prophase Animal Cell Plant Cell Photographs from: Prophase The cell prepares for nuclear division Animal and Plant Cell Packages DNA into chromosomes nuclear envelope breaks down Centrosomes move apart and forms spindle which guides chr. separation Metaphase Animal Cell Plant Cell Photographs from: Metaphase The cell prepares chromosomes for division Animal and Plant Cell Chromosomes line up at the center of the cell Spindle fibers attach from daughter cells to chromosomes at the centromere Anaphase Animal Cell Plant Cell Photographs from: Anaphase The chromosomes divide Animal and Animal Cell Spindle fibers pull chromosomes apart of each chromosome (called chromotid) moves to each daughter cell Telophase Animal Cell Plant Cell Photographs from: Telophase The cytoplasm divides Animal Cell chromosomes uncoil 2 nuclei form spindle breaks down nuclear envelope and nucleoli reappear