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Notes –Cell Growth and Division: Mitosis Name Per Directions On another sheet of paper copy down the vocabulary. Highlight the main topic of each paragraph. Next underline the supporting facts of the main topic. Circle examples of the supporting facts. Provide an appropriate title for each section. Once the first reading is complete go back and provide questions and examples along the left side. Along the right side, place a + to indicate understanding and a – to indicate needing clarification. Notes Title of Paragraph When a living organism grows, what happens to its cells? Nearly all cells can grow by increasing in size. However, as cells increase in size they become less efficient. The larger the cell becomes, the more demands the cell places on its DNA. In addition, larger cells are less efficient in moving nutrients and wastes materials across the semipermeable cell membrane. The ratio of surface area to volume Title of Paragraph The reasons for the inefficiency when a cell gets too large is that the surface area to volume ratio gets smaller as the cell gets larger. Thus, if the cell grows beyond a certain limit, not enough material will be able to cross the membrane fast enough to accommodate the increased cellular volume. Remember a ratio is a comparison. In this case, it compares the amount of surface area a cell hast to its volume. A ratio can be expressed as a proportion, such as 2:1 or as a fraction, such as 2/1. Title Before a cell becomes too large, a growing cell divides making two daughter cells. Daughter cells are genetically identical to the parent cell because they contain the same number and type of chromosomes. The process in which a cell divides into two new, identical daughter cells is called cell division. Title As learned in chapter 7, there are many organelles with specialized function in cells. What would happen if cells simply split to these organelles? The result might be disastrous. Importantly, if some of the genetic material was missing in the new daughter cell, they would not be able to carry out cellular functions. Thus, a cell first must make a complete copy of their genetic material before dividing. Title Even a small molecule like the bacterium E. coli has a tremendous amount of deoxyribonucleic acid (DNA). The DNA in human cells is about 2 meters long, but coiled so tightly it fits into the nucleus. If all the DNA in all your cells were put together it would stretch to about 1000X the distance between the Earth and sun. The DNA fits into eukaryotic cell nuclei because it is tightly bundled into packages of DNA known as chromosomes. Title Eukaryotic cells generally have much more DNA than prokaryotic cells (bacterial), thus have multiple chromosomes. Fruit flies, for example have 8 chromosomes per cell, carrots 18 per cell, chimpanzees 48 per cell and humans 46 per cell. The chromosomes in eukaryotic cells form close association with histones, a type of protein. The complex protein and chromosome is referred to as chromatin. Chromosomes make it possible to separate DNA precisely during cell division. Title Eukaryotic cell division is divided into interphase, G1 phase, G2 phase S phase, and the M phase (mitosis and cytokinesis). Cells do most of their growing in the G1 Phase: Cell growth. Cells also synthesize (make) new proteins and organelles. During the S Phase new DNA is synthesized when the chromosomes are replicated. If humans have 46 chromosomes, how many are present after the S phase? . During G2 Phase more molecules and organelles necessary for active cell division are made. The final phase is the M phase, which includes mitosis and cytokinesis. Mitosis is where the two identical daughter cells are made. Mitosis is a type of asexual cell division that results in two identical daughter cells. Label S, G2, M, mitosis, and cytokinesis Events Summary of Event G1 S G2 M Phase: Mitosis M Phase: Cytokinesis Biologists divide the events of mitosis into four phases: prophase, metaphase, anaphase, and telophase. In the following reading, also use pages 282- 284 of Miller and Levine. Title The first phase is prophase, and is usually the longest. During prophase the genetic material inside the nucleus condenses and the duplicated chromosomes become visible. Outside the nucleus, a spindle starts to form. The duplicated strands of chromosomes are connected along an area called a centromere. Each DNA strand in the duplicated chromosome is referred to as a chromatid, or sister chromatid. Also during prophase, the cell starts to build a spindle, a fanlike system of microtubules (stringy-like) that will connect the centromeres and help pull the duplicated chromosomes apart. Spindle fibers attach to centrioles at the opposite ends of each cell. The centrioles act like anchors to hold the spindle fibers in place. Draw and label the picture in prophase – centromeres, nuclear envelope, chromatid or chromosomes, spindle fibers, and centriole Phase Title The second phase is metaphase, and is generally the shortest. During metaphase, the centromeres of the duplicated chromosomes line up across the center of the cell. Spindle fibers connect to the centromeres of each chromosome and to the centrioles. Draw and label centromeres, chromatid or chromosomes, spindle fibers, and centriole. What structure is not present in metaphase that was labeled in prophase? . Phase Title The phase where the chromosomes separate is celled anaphase. As the spindle fibers shorten the chromosomes are pulled apart at the centromere to opposite ends of the cell. Draw and label the following in anaphase – centromeres, spindle fibers, centriole, chromosomes. Title Following anaphase is telophase. During telophase, the chromosomes, which were distinct and condensed, began to spread out into a tangle of chromatin. The nuclear envelope begins to reform. The spindle and centrioles begin to break apart. Draw and label, the nuclear envelop, chromatin, spindle fibers, and centrioles. Phase Title As a result of mitosis, two nuclei, each with a complete set of chromosomes- are formed, which is the goal of mitosis. The last phase of cell division is cytokinesis. Cyto means cell and kinesis means to move. Eukaryotic cells pinch together to form two new cells - the cytoplasm and organelles within the cytoplasm divide. Think: Why do cells need to divide?