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Transcript
Cell Growth and Division Cell Size, Cell Cycle, and Uncontrolled Cell Division 37.2 Trillion Cells in the Human Body Limits to Cell Size As the cell grows, two problems arise… Demands on DNA ● DNA controls the processes of the cell. ● As the cell grows, no extra DNA is made but more demand is put on the DNA. Nutrient Exchange ● ● Food, O2, and H2O enter and wastes exit across the membrane Must understand surface area and volume ○ Exchange rate depends on surface area of membrane ○ Rate of waste production depends on the cell’s volume As the cell grows, two problems arise… Demands on DNA Example: Small town library has enough books for people to borrow. However, if a lot of people move into town, some people may have to wait for popular books (more demand). Nutrient Exchange Example: It is easier to transport materials in a swimming pool than the ocean Volume increases at a faster rate than Surface area This is a problem for the cell! Example: Traffic increases as size of city increases, but the roads stay the same size. Calculations: Surface Area = length x width x # of sides Volume = length x width x height 1 cm SA= 6 cm2 Volume= 1 cm3 SA/Volume ratio= 6:1 2 cm SA= 24 cm2 Volume= 8 cm3 SA/Volume ratio= 3:1 SA/Volume Ratio The lower the SA/Volume ratio, the harder it is to get material into/out of the cell. So what does the cell do instead? It divides!! This is called Cell Division ● A cell divides into 2 daughter cells ● Cell copies all of its DNA ● Each cell will get a copy of the DNA Solves DNA problem as well as reducing the cell's volume so that materials can be exchanged across the membrane. So whose cells are bigger… an adult or a baby? It divides!! This is called Cell Division ● ● ● A cell divides into 2 daughter cells Cell copies all of its DNA Each cell will get a copy of the DNA Solves DNA problem as well as reducing the cell's volume so that materials can be exchanges across the membrane. We wrote this down last time, just reviewing! Why do cells need to divide? Do they divide at the same rate? 2 main reasons Growth Repair THE CELL CYCLE ● 3 main stages of the cell cycle: ○ Interphase ○ Mitosis ○ Cytokinesis Interphase: growth and DNA replication Mitosis: division of the cell nucleus Cytokinesis: division of the cytoplasm Before we go over each of the phases, let’s talk about DNA... - During interphase, it is in chromatin form (Depictions often look like Ramen) - During mitosis, it condenses into X shape called chromosomes - Humans have 46 chromosomes (23 pairs) in their body (somatic) cells Chromosomes Sister The Cell Cycle Broken down Mitotic phase has 4 phases: Interphase is divided into 3 sections: 1. G1(Gap 1) 2. S (synthesis) 3. G2 (Gap 2) Prophase Metaphase Anaphase Telophase ____________________________ Cytokinesis: when 1 cell becomes 2 - Completed by the end of Telophase Interphase DNA in chromatin form Nucleolus visible 1. G1(Gap 1): everyday life of cell 2. S (synthesis): DNA replicates 3. G2 (Gap 2): All organelles replicate Prophase DNA condenses into X shape (chromosomes) Nuclear membrane breaks down Centrioles migrate to opposite sides of nucleus The spindle forms and chromosomes attach at centromere Metaphase The spindle fibers pull the chromosomes by their centromeres until they line up down the middle *M=metaphase=middle Anaphase Centromeres of the sister chromatids split The individual chromatids separate Spindle fibers move them to opposite sides A for Anaphase -- Chromatids looks like A’s. Telophase Spindle fiber breaks down Two new nuclear membrane returns “Pinch” forms in the middle Cytokinesis Cytoplasm pinches in half One cell becomes two cells Each cell has identical set of chromosomes Mitosis Summary and Animation When does the nuclear membrane breakdown? Reform? Prophase; Telophase T/F: Chromatids are pulled to opposite sides in Metaphase. False; Anaphase A . Interphase B. Telophase C. Prophase D. Metaphase E. Anaphase So how quickly are cells replacing themselves? Video What is telling the cell it is time to divide? Cyclins - proteins that regulate the timing of the cell cycle What about uncontrolled cell division? Cancer A disorder in which some of the body’s own cells lose the ability to control growth. These cells do not respond to the regulators of normal cells Tumors can grow and cause damage to normal tissues. Truth or Myth?