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ESSENTIAL QUESTION: WHAT ARE THE FOUR STAGES OF MITOSIS? THINK-PAIR-SHARE Why are cells small? Why would it be bad for them to grow too large? CELL CYCLE RE-CAP 1. 2. 3. 4. G1 S phase G2 M phase Remember that G1, S, and G2 together are known as interphase and a cell spends most of it’s life in interphase. REASONS FOR CELL DIVISION 1. To prevent them from being inefficient in getting nutrients 2. To reproduce 3. For example: bacteria can reproduce asexually To repair damaged tissue 4. surface area to volume ratio For example: if you get a paper cut To grow an organism MITOSIS IN THE CELL There are many words that describe DNA in it’s various forms… A. DNA is usually found as chromatin while the cell is doing its normal job. 1. Chromatin is the granular material visible within the nucleus that consists of DNA tightly coiled around proteins. B. BEFORE A CELL DIVIDES, CHROMATIN (DNA) COILS UP TO FORM CHROMOSOMES. 1.CHROMOSOMES ARE MADE UP OF DNA AND PROTEINS. 2. ALL ORGANISMS DO NOT HAVE THE SAME NUMBER OF CHROMOSOMES. 3. HUMAN CELLS HAVE 46 CHROMOSOMES. 4. CHROMOSOMES ARE ONLY VISIBLE DURING CELL DIVISION. C. BEFORE EACH CELL DIVISION, EACH CHROMOSOME IS REPLICATED, OR COPIED. D. FOR THIS REASON, EACH CHROMOSOME CONSISTS OF TWO IDENTICAL SISTER CHROMATIDS. E. EACH PAIR OF SISTER CHROMATIDS IS ATTACHED AT AN AREA CALLED THE CENTROMERE. A HUMAN BODY CELL ENTERING CELL DIVISION CONTAINS 46 CHROMOSOMES OR 92 CHROMATIDS. NOW LET’S TALK ABOUT MITOSIS… II. THE TWO MAIN STAGES OF CELL DIVISION ARE MITOSIS AND CYTOKINESIS. Cyto = Cell Kinesis = Movement A. THE FIRST STAGE, DIVISION OF THE CELL NUCLEUS, IS CALLED MITOSIS. B. THE SECOND STAGE, DIVISION OF THE CYTOPLASM, IS CALLED CYTOKINESIS. C. REPRODUCTION BY MITOSIS IS CLASSIFIED AS ASEXUAL. 1. UNICELLULAR ORGANISMS REPRODUCE IN THIS MANNER. 2. MITOSIS IS ALSO THE SOURCE OF NEW CELLS WHEN A MULTICELLULAR ORGANISM GROWS AND DEVELOPS. D. AS YOU REMEMBER, A CELL SPENDS MOST OF ITS TIME IN INTERPHASE. DURING INTERPHASE, A CELL DOES ITS NORMAL JOB, GROWS LARGER, COPIES ITS DNA, AND PREPARES FOR CELL DIVISION. DRAW THIS! III. MITOSIS A. BIOLOGISTS DIVIDE THE EVENTS OF MITOSIS INTO PHASES: PROPHASE, METAPHASE, ANAPHASE, AND TELOPHASE (PMAT). 4 DURING PROPHASE, THE CHROMOSOMES BECOME VISIBLE, THE CENTRIOLES SEPARATE TO OPPOSITE SIDES OF THE CELL, THE CHROMOSOMES ATTACH TO THE SPINDLE, THE NUCLEOLUS DISAPPEARS, AND THE NUCLEAR ENVELOPE BREAKS DOWN. DRAW THIS! B. THE CENTRIOLES ARE TWO TINY STRUCTURES LOCATED IN THE CYTOPLASM NEAR THE NUCLEAR ENVELOPE THAT HELP ORGANIZE THE SPINDLE. C. THE SPINDLE FIBERS ARE A FANLIKE MICROTUBULE STRUCTURE THAT HELPS SEPARATE THE CHROMOSOMES. DURING METAPHASE, THE CHROMOSOMES LINE UP ACROSS THE CENTER OF THE CELL (MIDDLE). DURING ANAPHASE, THE CENTROMERES THAT JOIN THE SISTER CHROMATIDS SPLIT AND THE CHROMOSOMES MOVE UNTIL THEY HAVE SEPARATED INTO TWO GROUPS NEAR THE POLES OF THE SPINDLE (AWAY). DRAW THIS! DURING TELOPHASE, THE CHROMOSOMES BEGIN TO DISPERSE INTO A TANGLE OF DENSE MATERIAL, THE NUCLEAR ENVELOPE REFORMS AROUND EACH CLUSTER OF CHROMOSOMES, THE SPINDLE BREAKS APART, AND THE NUCLEOLUS BECOMES VISIBLE IN EACH NUCLEUS. DRAW THIS! Always remember… P M A PROPHASE METAPHASE TELOPHASE ANAPHASE T D. CELL DIVISION IS NOT COMPLETE AFTER TELOPHASE. CYTOKINESIS IS DIVISION OF THE CYTOPLASM. IN ANIMAL CELLS, CYTOKINESIS OCCURS WHEN THE CELL MEMBRANE IS DRAWN INWARD UNTIL THE CYTOPLASM IS PINCHED INTO TWO EQUAL PARTS. IN PLANT CELLS, CYTOKINESIS OCCURS WHEN A CELL PLATE FORMS CLEAVAGE FURROW BETWEEN THE DIVIDED NUCLEI GRADUALLY DEVELOPING INTO A SEPARATING MEMBRANE. MITOSIS IN THE CELL LET’S PRACTICE… On the back of your page, number 1-5. On the next slide, you will see 5 pictures. You need to figure out what phase each one is in and write it down. 1 2 4 3 5