Basic Chromosome Structure And other structures important in cell division Chromatin Loosely packed mass of DNA and proteins (histones) Normal form for DNA Anatomy of a Chromosome Chromosome – compact DNA structure Sister chromatids – identical joined copies of a chromosome Centromere – region where sister chromatids are joined Sister chromatids Mitosis as Part of the Cell Cycle Events and illustrations of cell division S phase G1 phase G2 phase Growth The period of cell growth is called interphase. The cell spends the majority of its life in interphase. Interphase is composed of 3 parts: G1, S, G2 Write small and abbreviate! G1: Gap 1 The G1 phase gene expression and protein synthesis. Cell grows and carries out normal functions S Phase: DNA Synthesis During S phase, the cell replicates its DNA. Remember: the cell needs 2 complete sets of DNA to divide into two daughter cells, each with a complete copy of DNA. G2: Gap 2 During the G2 phase, the cell prepares to divide More growth gene expression Once this is complete the cell is ready for division! Centrioles Chromatin Interphase Nuclear envelope Cytokinesis Nuclear envelope reforming Telophase Anaphase Individual chromosomes Metaphase Centriole Spindle Centriole Chromosomes (paired chromatids) Prophase Centromere Spindle forming This is what the cell looks like in interphase! Cells in Interphase Mitosis Mitosis = division of the nucleus Result= two identical nuclei The Four Steps of Mitosis 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase Mitosis is described as a series of steps. The four steps are: The acronym PMAT may help you remember the phases in order! Centrioles Chromatin Interphase Nuclear envelope Cytokinesis Nuclear envelope reforming Telophase Anaphase Individual chromosomes Metaphase Centriole Spindle ends (poles) of the cell. Threadlike spindle fibers begin to stretch across the cell making a football-shaped network of fibers. Centrioles Chromatin Interphase Nuclear envelope Cytokinesis Nuclear envelope reforming Telophase Anaphase Individual chromosomes Metaphase Centriole Spindle Centriole Chromosomes (paired chromatids) Prophase Centromere Spindle forming This is what the cell looks like in metaphase! Step 2 - Metaphase To remember metaphase, think “M” for “middle” The double-stranded chromosomes line up at the center of the cell. Each centromere becomes attached to a spindle fiber. Centrioles Chromatin Interphase Nuclear envelope Cytokinesis Nuclear envelope reforming Telophase Anaphase Individual chromosomes Metaphase Centriole Spindle Centriole Chromosomes (paired chromatids) Prophase Centromere Spindle forming This is what the cell looks like in anaphase! Step 3 - Anaphase To remember anaphase, think “A” for “apart” Double stranded chromosomes divide (pull apart). Each centromere divides. Sister chromatids separate. The separate chromatids move away from each other toward the poles of the cell. Centrioles Chromatin Interphase Nuclear envelope Cytokinesis Nuclear envelope reforming Telophase Anaphase Individual chromosomes Metaphase Centriole Spindle Centriole Chromosomes (paired chromatids) Prophase Centromere Spindle forming This is what the cell looks like in telophase! Step 4 - Telophase Telophase is the last step in mitosis. Centrioles and spindle fibers disappear. The chromosomes relax into chromatin. A nuclear membrane forms at each end of the cell. Two nuclei, one cell Can You Find Cells in the Different Phases of Mitosis? Interphase Early prophase Early Metaphase Anaphase Telophase In most organisms, once the nucleus has divided, the cytoplasm also separates and two whole new cells are formed. Cytokinesis - The Cell Divides Animal Cells Animal cells begin cytokinesis when the the cell membrane begins to pinch inward. This processes creates a cleavage furrow, which eventually results in 2 new cells. Cleavage Furrow Plant Cells Plant cells have rigid cell walls. They can not and do not pinch apart as animal cells do. Instead, a structure called a cell plate forms between the two new nuclei. A new cell wall forms along the cell plate and eventually divides the cell. Cell Plate Centrioles Chromatin Interphase Nuclear envelope Cytokinesis Nuclear envelope reforming Telophase Anaphase Individual chromosomes Metaphase Centriole Spindle Centriole Chromosomes (paired chromatids) Prophase Centromere Spindle forming This is what the cell looks like in cytokinesis!