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Transcript
The Process of Cell Division (10.2) Chromosomes Chromosomes: packages of DNA, or genetic information Before dividing, the cell needs to prepare and copy its DNA Prokaryotic Chromosomes - DNA is found in the cytoplasm due to no nucleus - Most contain a single, circular DNA chromosome that contains all the genetic information Chromosomes Cont. Eukaryotic Chromosomes - Eukaryotes have more genetic information compared to prokaryotes → more chromosomes - Chromatin: unraveled for of DNA - - composed of chromosomes and histone protein DNA + chromosomes = nucleosomes - Chromosomes make it possible to separate DNA precisely during cell division Eukaryotic Chromosomes Cell Cycle Cell Cycle: The cell grows, prepares for division, and divides to form two daughter cells Prokaryotic Cell Cycle (Binary Fission) - Once they grow to a certain size, the cell copies its DNA - the 2 DNA chromosomes attach to different regions of the cell membrane - a network of fibers forms between them stretching to the opposite side of the cell - the fibers constrict and pinch inwards dividing the cytoplasm and chromosomes Binary fission: the production of two genetically identical cells Binary Fission Cell Cycle Eukaryotic Cell Cycle - Interphase: one division after another separated by an “in-between” variation of growth 1. G1--Cell Growth: most cell growth happens now with increased cell size and protein production 2. S--DNA Replication: new DNA is synthesized when chromosomes are replicated 3. G2--Preparing for Cell Division: is the shortest phase when organelles need for replication are produced 4. M--Cell Division: quick cell division in the form of mitosis 5. Mitosis: division of the nucleus 6. Cytokinesis: division of the cytoplasm Eukaryotic Cell Cycle Mitosis Mitosis: the division of the cell nucleus Divided into 4 phases: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase Prophase Prophase: the genetic material inside the nucleus condenses and the duplicate chromosomes become visible. Outside the nucleus, a spindle starts to form. - Usually the longest (½ time) - Centromere: the area where the duplicate DNA strands connect - Chromatid: each DNA strand in the duplicate chromosome - - when mitosis is complete, the chromatids will separate between the two new daughter cells Centrioles: parts made of microtubules that are built like a spindle and extend from the centrosome - Centrioles begin to move towards opposite poles and the nucleolus disappears towards the end Prophase Metaphase Metaphase: the centromeres of the duplicated chromosomes line up across the center of the cell. Spindle fibers connect the centromere of each chromosome to the two poles of the spindle. - Generally the shortest phase Anaphase Anaphase: the chromosomes (sister chromatids) separate and move along spindle fibers to opposite ends of the cell - sister chromatids are considered individual chromosomes when anaphase begins - end: when the sister chromatids are completely separated into two sides Telophase Telophase: the chromosome, which are distinct and condensed, begin to spread out into a tangle of chromatin - nuclear envelope reforms around each set of chromosomes - spindle fibers begin to break apart - nucleolus becomes visible Cytokinesis Cytokinesis: the division of cytoplasm; splitting one cell into two completely separate cells (daughter cells) Animal Cells → cell membrane draws inward creating a cleavage furrow until the two cells pinch apart Plant Cells → a cell plate forms halfway between the divided nuclei; the cell plate develops into a cell membrane and separates the two cells; a cell wall forms between the two membranes completing the process Plant vs. Animal Cytokinesis