CHAPTER 9 CELLULAR REPRODUCTION P. 243-257
SECTION 9-1 CELLULAR GROWTH Page 244
ESSENTIAL QUESTION Why is it beneficial for cells to remain small?
MAIN IDEA Cells grow until they reach their size limit, then they either stop growing or divide.
CELL SIZE LIMITATIONS Most cells are smaller than a period at the end of a sentence. There are two reasons cells divide rather that continue to grow. The larger the cell becomes, the more demands the cell places on it DNA. The larger the cell becomes, the more trouble the cell has moving nutrients and wastes across the cell membrane.
HOW DOES THE AMOUNT OF SURFACE AREA CHANGE AS THE CELL S VOLUME INCREASES?
RATIO OF SURFACE AREA TO VOLUME The key factor that limits the size of a cell is the ratio of its surface area to volume. The surface area refers to the area covered by the plasma membrane. The volume refers to the space taken by the inner contents of the cell, including the organelles in the cytoplasm and the nucleus.
HOW DOES THE AMOUNT OF SURFACE AREA CHANGE AS THE CELL S VOLUME INCREASES?
RATIO OF SURFACE AREA TO VOLUME As a cell grows in size, its volume increases faster than its surface area. This means the cell might have trouble supplying and transporting nutrients and expelling enough waste products. By remaining small, cells can sustain themselves more easily.
CELL CYCLE Once a cell reaches its size limit, it will either stop growing or divide. Most cells divide. Nerve and muscle cells do not divide. Cell division also is the way the cell reproduces so that you grow and heal certain injuries. Cells reproduce by a cycle of growing and dividing called the cell cycle.
CELL CYCLE 3 main stages.. Interphase cell grows, carries out certain cellular functions, replicates its DNA [3 substages] Mitosis cell s nucleus and nuclear material, DNA, divide [4 substages] Cytokinesis cytoplasm divides
CELL CYCLE
STAGES OF INTERPHASE G1 stage (normal cell growth) has the longest duration. G1-1 st stage, a cell is growing, carrying out normal cell functions, and preparing to replicate or copy DNA S - 2 nd stage, cell copies its DNA in preparation for cell division Chromosomes contain the genetic material that is passed from one generation to the next.
STAGES OF INTERPHASE Chromatin is the relaxed form of DNA in a cell s nucleus. Chromatin condenses or tightens to form chromosomes. G2-3 rd stage, Cell prepares for the division of its nucleus. The cell makes sure everything is ready for mitosis. A cell spends the majority of its lifetime in interphase.
SECTION 9-2 MITOSIS AND CYTOKINESIS Page 248
MAIN IDEA Eukaryotic cells reproduce by mitosis, the process of nuclear division, and cytokinesis, the process of cytoplasmic division.
MITOSIS AND CYTOKINESIS
PHASES OF MITOSIS - PROPHASE 1 st phase - longest Chromatin tightens into chromosomes that are X-shaped and become visible. Centrioles separate and move to opposite poles of the cell. Nuclear membrane disintegrates. Nucleolus disappears. Mitotic spindle begins to form between the poles.
CHROMOSOMES
PROPHASE xxxx xxxx xxxx
PROPHASE Spindle apparatus is made of spindle fibers, centrioles, and aster fibers. The spindle apparatus is important in organizing and moving chromosomes before cell division. Plant cells do not have centrioles.
BY THE END OF PROPHASE, THE FOLLOWING HAS OCCURRED: By the end of prophase, the following has occurred: Nuclear envelope seems to disappear. Spindle fibers attach to sister chromatids on both sides of the centromere.
METAPHASE 2 nd phase - shortest Sister chromatids are pulled along the spindle apparatus to center of cell and line up in the middle. Tension of spindle fibers pulls them along.
METAPHASE xxx
ANAPHASE 3 rd phase The centromeres that join the sister chromatids split. The sister chromosomes become individual chromosomes. The two sets of chromosomes move apart to opposite poles.
ANAPHASE
TELOPHASE 4 th phase - last phase Chromosomes gather at opposite ends of the cell and lose their shape. Two new nuclear envelopes form. Nucleoli reappear. Spindle apparatus comes apart.
TELOPHASE
CYTOKINESIS Cytokinesis usually happens at the same time as telophase. The cell membrane is pulled inward until the cytoplasm is pinched into two nearly equal parts. Results are two cells, with identical nuclei. In plant cells, a cell plate forms that later becomes cell wall to divide the cells.
CYTOKINESIS
SECTION 9-3 CELL CYCLE REGULATION Page 253
MAIN IDEA The normal cell cycle is regulated by cyclin proteins.
CYCLINS In a multicellular organism, cell growth and cell division are carefully controlled. When an injury such as a cut in the skin occurs, cells at the edge of the cut divide rapidly. When the healing process is nearly complete, the rate of cell division slows and then returns to normal.
CYCLINS When cells come into contact with one another, molecules on their surface signal them to stop growing. Cyclins, a group of proteins, regulate the timing of the cell cycle in eukaryotic cells. Cyclins are one group of proteins involved in cell cycle regulation. Other proteins, called regulatory proteins, regulate the cell cycle in different ways.
CANCER Contols on cell growth can be turned on and off by the body. Cancer is a disorder in which some of the body s cells lose the ability to control growth. Cancer cells do not respond to the signals that control the growth of most cells. As a result, cancer cells divide uncontrollably.
CANCER Cancer cells reproduce rapidly because they spend less time in interphase. Cancer cells do not stop growing when they touch other cells. They continue to grow and divide until their supply of nutrients is used up.
CANCER CAN BE CAUSED BY. Changes that occur in the regulation of cell growth and division of cancer cells are due to mutations or changes in segments of DNA. The changes can damage the control of the proteins that regulate the cell cycle. The genetic change or damage can often be repaired by various repair systems If repair systems fail, cancer can result.
CARCINOGENS Various environmental factors can affect the occurrence of cancer cells. Substances that are known to cause cancer are called carcinogens. Examples: cigarettes, asbestos, X rays, the Sun s ultraviolet rays
APOPTOSIS Apoptosis is programmed cell death. Cells going through apoptosis actually shrink and shrivel in a controlled process. Example: When hands and feet begin to develop, there are cells between fingers and toes that look like webbing. The webbing is not present in the mature organism.
STEM CELLS Most cells in a nulticellular organism are designed for a specialized function. Stem cells are unspecialized cells that can develop into specialized cells when under the right conditions. Two basic types of stem cells: Embryonic- After a sperm terilizes an egg, the resulting mass of cells divides until there are about 100-150 cells.
STEM CELLS Adult- Found in various tissues in the body and might be used to maintain and repair the same kind of tissue where they are found. Researchers think certain kinds of adult stem cells might be able to develop into different kinds of cells for treatment of disease and conditions.