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Chapter 9 Cell Growth and Division Cell Growth When a living thing grows, what happens to its cells? Do they just get larger and larger? An adult’s cells are about the same size as a baby’s– there are just more of them As an organism grows, the cells get as large as they can, and then they divide and produce two new cells Limits to Cell Growth A cell divides instead of continuing to grow larger and larger. This is because there are specific limits on cell growth DNA Overload: Imagine if the Media Center only had 3 books. Would that be enough for all the students at WHS? If the cells get too large, then there isn’t enough information, or DNA, to make the proteins needed for life. Limits to Cell Growth, Cont. Exchanging Materials- Imagine 4 students in the gym passing an egg back and forth to each other. Is it easier or harder for these 4 students in the gym or in Mrs. C’s classroom? If the cell gets too big, food, gases and such cannot easily travel through the cell Surface area and volume: The volume of the cell grows faster than the surface area of the cell membrane. There isn’t enough room on the membrane to get enough stuff in and out of the cell for the increasing volume– this can cause major problems! Solving These Issues Because of DNA overload, exchanging materials and surface area and volume, a cell must divide in order to continue working properly. This is called cell division, where one cell divides into two “daughter cells” which are genetically identical to the parent cell. DNA is replicated before division, so each cell gets their own copy of DNA Cell Division Chromosomes- DNA and protein condense to form chromosomes which lives in the nucleus and carries the cell’s coded genetic information Each chromosome is made out of two sister chromatids and attached at the center by the centromere The Cell Cycle During the cell cycle, a cell grows, prepares for division and divides– and then starts the cycle all over again Interphase– preparation for division. Contains three parts, G1, S and G2 G1- Cells increase in size S- All DNA is replicated G2- organelles and other molecules needed for division are reproduced The Cell Cycle, Cont. The “M” Phase, known as Mitosis (division of the nucleus) Prophase- Chromatin condenses into chromosomes and the centrioles separate. Spindles form and the nuclear envelope starts to break down M Phase, Cont Metaphase- Chromosomes line up down center of the cell, each chromosome is connected to a spindle fiber by the centromere M Phase, Cont Anaphase- Sister chromatids separate and are moved apart and start to travel to the other side of the separating cell M Phase, Cont. Telophase- The chromosomes gather at the opposite ends of the cell and lose their distinct shapes. Two new nuclear membranes form M Phase, Cont. Cytokinesis- the cytoplasm splits and two new cells are formed. In plant cells, a cell plate is formed. Regulating the Cell Cycle Controls on cell division include internal and external regulators. Regulators don’t allow the cell cycle to progress until all the stages have happened OR tell the cell cycle to stop so no more cells are made Internal- Cyclins are proteins that keep the cell on the right track External– If a cell contacts another cell, then the cells will stop making new ones Uncontrolled Cell Growth Cancer is a disorder in which affected cells continue to grow when they shouldn’t. Cancer cells lack or have a defect in gene p53, which normally halts the cell cycle when needed Uncontrolled cell growth forms masses of tissues called tumors Cancer can be caused by: genetics, smoking, chemicals, radiation exposure, certain viruses Something that causes cancer is called a carcinogen Your assignment after notes Draw, Label, Title and color the following: Page 244-245, figures 10-3 and 10-4 Page 246-247, Figure 10-5 Page 248 figure 10-6