Physical Science 8th grade (1).pdf

Figure 117 fats and oils are high energy molecules

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Figure 11.7: Fats and oils are high-energy molecules organisms use to store energy reserves. Figure 11.8: The hydrocarbon chains in saturated and unsaturated fats. saturated fat - a fat molecule in which each carbon is bonded with two hydrogen atoms. unsaturated fat - a fat molecule that has less hydrogen atoms than a saturated fat.
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230 U NIT 4 M ATTER AND C HANGE Figure 11.9: This small protein called erabutoxin B is the active ingredient in sea snake venon. Figure 11.10: The shape of a protein determines how it functions. amino acids - organic molecules that are the building blocks of proteins. Proteins Proteins are large molecules Proteins are basic molecular building blocks of cells and all parts of animals. Muscle, skin, blood, and internal organs contain proteins. Second only to DNA, proteins are among the largest organic molecules. A relatively small protein is shown in Figure 11.9. Proteins are made of amino acids Amino acids are the building blocks of proteins. Virtually all proteins found in animals are made from only 20 different amino acids . The amino acids in a protein form multiple chains that fold around each other in complex structures (Figure 11.10). Shape and function Only certain parts of a protein are chemically active. The shape of a protein determines which active sites are exposed. Many proteins work together by fitting into each other like a lock and key. This is one reason proteins that do the same function in one organism do not work in another organism. For example, a skin protein from an animal cannot replace a skin protein from a human. Amino acids from food are used to build proteins Food supplies new proteins that a body needs to live and grow. However, proteins from one organism cannot be used by another. Fortunately, the same 20 amino acids are found in proteins from almost all living things. In your body, digestion breaks down food protein into its component amino acids. Cells reassemble the amino acids into new proteins suitable for your body’s needs.
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231 11.2 P ROTEINS , F ATS , AND N UCLEIC A CIDS C HAPTER 11: T HE C HEMISTRY OF L IVING S YSTEMS Enzymes The control problem Thousands of chemical reactions are going on in your body each second, involving thousands of chemicals. The reactions proceed at just the right rate to produce energy as it is needed. When you exercise, the reaction rate increases because your body needs more energy. How does your body control its chemical reactions? The temperature problem Sugar (glucose) does not turn into water and carbon dioxide by itself. Outside the body, this reaction needs the intense heat of a flame. Yet your body causes this reaction to occur at only 37°C. How does the body cause reactions like this to occur at low temperature? The answer is that enzymes allow your body to initiate chemical reactions at low temperature and to control the rate of reactions.
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