Cell theory new cells arose within preexisting cells through cell division Virchow proposed cell division through mitosis or meiosis 194 209 211 227 Embryos newly developing organisms Meiosis leads to the production of sperm and eggs gametes reproductive cells Mitosis leads to the production of all other cell types somatic cells body belonging Cytokinesis cell movement the division of the cytoplasm into two distinct cells when this is complete a parent cell has given rise to two daughter cells accompanies mitosis and meiosis Mitosis Genetic material is copied then divided equally daughter cells are genetically identical to parent cell asexual reproduction Responsible for growth wound repair and reproduction Meiosis Daughter cells are genetically different from each other and have half the amount of hereditary material as the parent cell Chromosome Walter Flemming introduced the term mitosis mitos thread to describe division process threadlike structures chromosomes appear in pairs just before cell division then split to produce single unpaired threads in daughter cells Wilhelm Waldeyer coined the term chromosome single long DNA double helix wrapped around proteins in an organized manner DNA encodes the cell s hereditary info genetic material gene is a length of DNA that codes for a particular protein or RNA found in cell Duplicates prior to mitosis then condenses into compact structures to move around the cell easily Chromatid one of two identical strands composing a replicated chromosome that s connected at the centromere to the other strand a single chromosome consists of two chromatids Phases of MItosis takes 24 hours Interphase non dividing phase most time spent here cell is either growing and preparing to divide or fulfilling its specialized function in a multicellular individual constantly active chromosome uncoil into long thin structures Synthesis phase part of interphase replication of the genetic material is separated from the partitioning of chromosome copies during M phase lasts 6 8 hours to study cells Howard and Pelc exposed dividing cells to radioactive phosphorus or thymidine both incorporated into DNA as it s being synthesized 1 label DNA as chromosomes were being copied 2 wash away excess radioactive isotopes 3 autoradiography radioactive phosphorus thymidine create a black dot where active DNA synthesis is happening Conclusion came across S phase Mitotic phase dividing phase chromosome are only visible during this stage DNA replication during this phase Cell cycle coined by Howard and Pelc orderly sequence of events that starts with the formation of a eukaryotic cell which undergoes division through the duplication of its chromosomes Cultured cells are beneficially for experimenting because they can be manipulated more easily than cells in an intact organism Experiment Pulse chase approach introduce radioactive thymidine then flood it with nonradioactive thymidine labeled cells that were in any portion of S phase checked in 2 hour increments after Results none of labeled cells started mitosis immediately even if it was at the end of S phase took 4 hours to begin G2 phase second interval in the cell cycle between the end of the S phase and the beginning of the M phase G1 phase first gap which occurs after M phase but before S phase twice as long as G2 G1 S phase G2 M phase parent M phase two daughter cells The Cell Cycle interphase total of four phases Gaps provide the required time for the parent cell to grow large enough and synthesize enough organelles so its daughter cells will be a normal size and function How MItosis Takes Place Parent Cell has four un replicated chromosomes G1 phase chromosomes replicate to form two sister chromatids S phase chromatids condense G2 phase parent cell splits two form two identical daughter cells M phase Number of chromosomes vary between species Eukaryotic chromosomes has DNA associated with globular proteins histones this DNA material is called chromatin so chromatin is comprised of histones chromatins are in relaxed state during interphase Sister chromatids are composed of two double helixes same genetic info Attach together at centromere during M phase when chromatin condenses Last stage of M phase parent cell splits into two daughter cells with identical genetic information same chromosomes that parent cell had before replicating Events in MItosis IPPMAT Interphase five substages of m phase mitosis prophase prometaphase metaphase anaphase telophase cytokinesis cell division begins cell division is complete Prophase chromosomes condense into compact structures Spindle apparatus formed in the cytoplasm pull chromosomes to the poles of the cell during mitosis and push the poles of the cell away from each other consists of microtubules at the end of each spindle are polar microtubules that connect and overlap in the middle of the cell Kinetochore microtubules attach to the chromosomes Centrosomes contains a pair of centrioles microtubule organizing center Prometaphase nucleolus and nuclear envelope disappears after chromosomes condense kinetochore microtubules from each spindle attach to one of the two sister chromatids this makes a structure called the kinetochore located in the centromere region BASICALLy kinetochore microtubules connect to chromatids while polar molecules attach to each other these microtubules arise and are pulled by the centrioles and centrosomes which move to opposite poles lining the chromatids up the kinetochores Metaphase Chromatids complete migration to the middle of the cell centrosomes being at opposite poles Chromatids are lined up along an imaginary plane called the metaphase plate formation of the spindle apparatus is complete Anaphase Centromeres split making the sister chromatids pull apart and create independent chromosomes Kinetochore microtubules pull chromosomes to opposite poles of the cell while the poles are pushing away from each other causes pressure to eventually split End of anaphase each pole of the cell has identical complete collections of chromosomes that are identical to those of the parent cell before replication Telophase nuclear envelope begins to form around each set of chromosomes Spindle apparatus disintegrates Chromosomes begin to de condense Completion of mitosis two independent nuclei have formed Cytokinesis All other organelles have replicated prior to M phase Cytoplasm divides to form two separate daughter cells Plant Cytokinesis proteins in microtubules combine