Cell Division: SE Small Overview

CellDivisionSE Gizmos Worksheet Cells reproduce by splitting in half, a process called cell division. What do cells need to do between divisions to make sure that they don't just get smaller and smaller? a cell must grow. The genetic information of a cell is carried in its DNA (short for deoxyribonucleic acid). What do cells need to do between divisions to make sure that a full set of DNA gets passed on to each daughter cell? The DNA must be copied so there is a full set of DNA to pass on to each daughter cell. Look at the cells. Do they all look the same? no Of the 100 cells shown, how many are in the process of dividing? 5 Select the BAR CHART tab, and turn on Show numerical values. How many cells are in the interphase stage of their life cycle? 91 Based on these two observations, would you say that a cell spends most of its life cycle in interphase or in mitosis/cytokinesis? interphase I've noticed that the cell stays here the longest during interphase, Observe: Click Play and hold the cursor over the cell. Observe the and then when it's ready to start mitosis, it happens suddenly. cell as it divides several times. (This happens quickly!) What do Each time a cell divides, the number of cells increases exponenyou notice happening during this process? tially. The third stage of cell division is anaphase. Interphase It prepares itself by replicating all of its organelles and genetic material. During the interphase, all of the preparations are completed. G1, S, and G2 are the three stages of interphase. The cycle controls cell division. As a result, the previous stage of mitosis and cytokinesis precedes interphase. Prophase The nuclear membrane breaks down, the chromosomes condense and become visible, and the spindle apparatus forms at opposite poles of the cell. Metaphase The tetrads are arranged around the center by kinetochores motions in metaphase, with the two centromeres opposite each other, but the sister chromatids are not forced apart as they are in mitosis. Anaphase The chromatids that keep the chromosomes together loosen during anaphase. Each tetrad's two homologous chromatids are divided into two poles. Since each parent's chromosomes can go through either pole, this is another way to increase genetic diversity. Telophase The chromosomes are transferred to opposite ends, the nuclear envelope reforms, and the spindle is broken down, much as in mitosis. Remember that in mitosis, there are two chromosomes, not one. Cytokinesis The cell divides, resulting in two daughter cells with the same number and type of chromosomes as the parent cell. Analyze: Use your summaries and the Gizmo to answer the following questions: What are the four phases of mitosis? prophase metaphase anaphase telophase During which phase is the DNA duplicated? interphase What is the relationship between chromatin and chromosomes? chromatin condenses to form chromosomes during prophase. In which phase are chromatids pulled apart? anaphase What is the role of the centrioles? centrioles produce spindle fibers which assist in the arrangement of chromosome movement. In which phase does a new nuclear membrane develop? telophase A cell has a single line of chromosomes. What is the phase? metaphase 1/2 During which three phases are individual chromosomes no longer visible? interphase cytokinesis telophase Think and discuss: Why is it important that the cell's DNA is duplicated before cell division? If the cell's DNA weren't duplicated before cell division, then each daughter cell would only get half of a complete set of DNA. Challenge: Human cells have 46 chromosomes. Each chromosome consists of a pair of identical chromatids attached together by a structure called a centromere. Once the chromosome has split, each chromatid is called a daughter chromosome. At the end of cytokinesis, how many daughter chromosomes will be found in each cell? Explain. There will be 46 daughter chromosomes in each daughter cell. Each of the 46 original chromosomes splits into two daughter chromosomes, each cell contains two sets of 46 daughter chromosomes. 2/2