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Transcript
THE PROCESS OF CELL DIVISION Chapter 10 Section 2 CHROMOSOMES Cells carry LOTS of DNA DNA in E.Coli is ~ 1000X the length of the cell. Has to be packaged tight and safely Chromosomes Help for Cell Division KEY QUESTION What is the job of chromosomes in cell division? Chromosomes make it possible to separate DNA precisely in the cell. THE CELL CYCLE Cells divide all the time to make new cells. The series of cells growth and division is the cell cycle. Cell Grows Prepares for Division Divides get 2 Daughter cells PROKARYOTIC CELL CYCLE Steps Fast Binary Fission (asexual reproduction) Growth, DNA replication, Cell Division EUKARYOTIC CELL CYCLE 2 Parts: Interphase and Mitosis Steps of Interphase G1: Cell Growth S Phase: DNA Replication G2: Preparing for Cell Division Mitosis: Cell Division KEY QUESTION What are the main events in the cell cycle? During the cell cycle, a cell grows, prepares for division, and divides to form 2 daughter cells. The eukaryotic cell cycle has two parts: Interphase and Cell Division MITOSIS The nucleus is dividing continuously, but we have identified 4 phases: Prophase Metaphase Anaphase Telophase PROPHASE Chromatin coils up into chromosomes (packaged DNA) Chromosomes look like an X, the two separate V’s are called sister chromatids The centromere holds them together. The centromere also helps the chromosome with movement. Nucleolus disappears and the nuclear envelope disintegrates In animal cells, we use centrioles, they move to opposite ends of the cells and begin to release spindle fibers. METAPHASE Spindle fibers attach to the chromosome by the centromere, and the spindle fibers line them up in the middle of cell. There is a spindle fiber pulling the sister chromatid to each end of the cell. This way when they divide each new cell has an identical copy of the DNA. ANAPHASE Chromosomes split and the chromatid pairs are pulled to each end of the cell. The microtubules just shorted and pull the chromatids back toward the centrioles. Chromatids reach the opposite ends of the poles. New cells start to prepare Chromosomes unwind, to make proteins Spindle fibers break down Nucleolus reappears Nuclear envelope reforms until we get two nuclear double membranes around the new sets of chromosomes CYTOKINESIS Different for plants and animals. Why? Animals: plasma membrane pinches in along equator in telophase, keeps pinching until they form 2 new cells. Plants: Cell wall so it can’t pinch in, but a cell plate is formed on each side until the separation of the cells is complete. ANIMAL VS PLANT WHY DO WE NEED MITOSIS? We get 2 new cells that are identical to the parent cell. Carry out the same function as the parent cell. Unicellular vs. Multicellular Unicellular: asexual reproduction (usually binary fission for most unicellular organisms) Multicellular: making copies, or new cells STAGES OF MITOSIS ONION ROOT MITOSIS