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Supplemental Chapter Material 8.2, 8.3, 9.2 and 13.2 Standard 2: Cellular Structure B.2.1 – Describe features common to all cells that are essential for growth and survival, and explain their functions B.2.2 – Describe the structure of a cell membrane and explain how it regulates the transport of materials into and out of the cell and prevents harmful materials from entering the cell. B.2.3 – Explain that most cells contain mitochondria, the key sites of cellular respiration, where stored chemical energy is converted into useable energy for the cell and some cells, including many plant cells, contain chloroplasts, the key sites of photosynthesis, where the energy of light is captured for use in chemical work. Standard 2: Cellular Structure B.2.4 – Explain that all cells contain ribosomes, the key sites for protein synthesis, where genetic material is decoded in order to form unique proteins. B.2.5 – Explain that cells use proteins to form structures, including cilia and flagella, which allow them to carry out specific functions, including movement, adhesion and absorption. B.2.6 – Investigate a variety of different cell types and relate the proportion of different organelles within theses cells to their functions. Chloroplasts pp. 231 and 233 Photosynthesis takes place inside organelles called chloroplasts. Chloroplasts contain saclike photosynthetic membranes called thylakoids, which are interconnected and arranged in stacks known as grana. Chloroplasts Pigments are located in the thylakoid membranes. The fluid portion outside of the thylakoids is known as the stroma. Energy Collection pp. 235-237 Because light is a form of energy, any compound that absorbs light absorbs energy. Chlorophyll absorbs visible light especially well. When chlorophyll absorbs light, a large fraction of the light energy is transferred to electrons. These highenergy electrons make photosynthesis work. THINK ABOUT IT Why do chloroplasts contain so many membranes? When most pigments absorb light, they eventually lose most of that energy as heat. Chloroplasts avoid such losses. Membranes are the key to capturing light energy in the form of high-energy electrons. The Light-Dependent Reactions: Generating ATP and NADPH Thylakoids contain clusters of chlorophyll and proteins known as photosystems. Photosystems absorb sunlight and generate high-energy electrons that are then passed to a series of electron carriers embedded in the thylakoid membrane. Energy Totals pp. 256-259 In the presence of oxygen, the complete breakdown of glucose through cellular respiration results in the production of 36 ATP molecules. This represents about 36 percent of the total energy of glucose. The remaining 64 percent is released as heat. Steps in Translation pp. 368-370 Messenger RNA is transcribed in the nucleus and then enters the cytoplasm for translation. Steps in Translation Translation begins when a ribosome attaches to an mRNA molecule in the cytoplasm. As the ribosome reads each codon of mRNA, it directs tRNA to bring the specified amino acid into the ribosome. One at a time, the ribosome then attaches each amino acid to the growing chain. Steps in Translation Each tRNA molecule carries just one kind of amino acid. In addition, each tRNA molecule has three unpaired bases, collectively called the anticodon—which is complementary to one mRNA codon. The tRNA molecule for methionine has the anticodon UAC, which pairs with the methionine codon, AUG. Steps in Translation The ribosome has a second binding site for a tRNA molecule for the next codon. If that next codon is UUC, a tRNA molecule with an AAG anticodon brings the amino acid phenylalanine into the ribosome. Steps in Translation The ribosome helps form a peptide bond between the first and second amino acids— methionine and phenylalanine. At the same time, the bond holding the first tRNA molecule to its amino acid is broken. Steps in Translation That tRNA then moves into a third binding site, from which it exits the ribosome. The ribosome then moves to the third codon, where tRNA brings it the amino acid specified by the third codon. Steps in Translation The polypeptide chain continues to grow until the ribosome reaches a “stop” codon on the mRNA molecule. When the ribosome reaches a stop codon, it releases both the newly formed polypeptide and the mRNA molecule, completing the process of translation.