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Chapter 3

Chapter 3. 0. The Molecules of Life. Biology and Society: Got Lactose?. Lactose is the main sugar found in milk. Some adults exhibit lactose intolerance, the inability to properly digest lactose. Lactose-intolerant individuals are unable to digest lactose properly.

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Chapter 3

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  1. Chapter 3 0 The Molecules of Life

  2. Biology and Society: Got Lactose? • Lactose is the main sugar found in milk. • Some adults exhibit lactose intolerance, the inability to properly digest lactose. • Lactose-intolerant individuals are unable to digest lactose properly. • Lactose is broken down by bacteria in the large intestine producing gas and discomfort. There is no treatment for the underlying cause of lactose intolerance. • Affected people must • Avoid lactose-containing foods or • Take the enzyme lactase when eating dairy products © 2010 Pearson Education, Inc.

  3. Evolution Connection: Evolution and Lactose Intolerance in Humans • Most people are lactose-intolerant as adults: • African Americans and Native Americans — 80% • Asian Americans — 90% • But only 10% of Americans of northern European descent are lactose-intolerant © 2010 Pearson Education, Inc.

  4. Lactose tolerance appears to have evolved in northern European cultures that relied upon dairy products. • Ethnic groups in East Africa that rely upon dairy products are also lactose tolerant.

  5. Polymers are made by stringing together many smaller molecules called monomers. • A dehydration reaction • Links two monomers together • Removes a molecule of water • Organisms also have to break down macromolecules. • Hydrolysis • Breaks bonds between monomers • Adds a molecule of water • Reverses the dehydration reaction

  6. LARGE BIOLOGICAL MOLECULES • There are four categories of large molecules in cells: • Carbohydrates • Lipids • Proteins • Nucleic acids

  7. Carbohydrates • Carbohydrates are sugars or sugar polymers. They include • Small sugar molecules in soft drinks • Long starch molecules in pasta and potatoes

  8. Monosaccharides & Disaccharides • Monosaccharides are simple sugars that cannot be broken down by hydrolysis into smaller sugars. • Common examples are • Glucose in sports drinks • Fructose found in fruit • A disaccharide is • A double sugar • Constructed from two monosaccharides • Formed by a dehydration reaction

  9. Disaccharides include • Lactose in milk (see next slide) • Maltose in beer, malted milk shakes, and malted milk ball candy • Sucrose in table sugar • Sucrose is • The main carbohydrate in plant sap • Rarely used as a sweetener in processed foods • High-fructose corn syrup is made by a commercial process that converts natural glucose in corn syrup to much sweeter fructose.

  10. Galactose Glucose Lactose Figure 3.7

  11. processed to extract Starch broken down into Glucose converted to sweeter Fructose added to foods as high-fructose corn syrup Ingredients: carbonated water, high-fructose corn syrup, caramel color, phosphoric acid, natural flavors Figure 3.8

  12. Polysaccharides • Polysaccharides are • Complex carbohydrates • Made of long chains of sugar units and polymers of monosaccharides • Examples include: starch, glycogen and cellulose

  13. Glucose monomer Starch granules a Starch Glycogen granules b Glycogen Cellulose fibril Cellulose molecules c Cellulose Figure 3.9

  14. Starch is • A familiar example of a polysaccharide • Used by plant cells to store energy • Potatoes and grains are major sources of starch in the human diet. • Glycogen is • Used by animals cells to store energy • Converted to glucose when it is needed • Cellulose • Is the most abundant organic compound on Earth • Forms cable-like fibers in the tough walls that enclose plants • Cannot be broken apart by most animals

  15. Lipids • Lipids are • Neither macromolecules nor polymers • Hydrophobic, unable to mix with water

  16. Oil (hydrophobic) Vinegar (hydrophilic) Figure 3.10

  17. Fats • A typical fat, or triglyceride, consists of a glycerol molecule joined with three fatty acid molecules via a dehydration reaction.

  18. Fatty acid Glycerol (a) A dehydration reaction linking a fatty acid to glycerol (b) A fat molecule with a glycerol “head” and three energy-rich hydrocarbon fatty acid “tails” Figure 3.11

  19. Fats perform essential functions in the human body including • Energy storage • Cushioning • Insulation

  20. Most animal fats • Have a high proportion of saturated fatty acids • Can easily stack, tending to be solid at room temperature • Contribute to atherosclerosis, a condition in which lipid-containing plaques build up within the walls of blood vessels

  21. Most plant oils tend to be low in saturated fatty acids and liquid at room temperature. • Hydrogenation • Adds hydrogen • Converts unsaturated fats to saturated fats • Makes liquid fats solid at room temperature • Creates trans fat, a type of unsaturated fat that is even less healthy than saturated fats

  22. TYPES OF FATS Saturated Fats Unsaturated Fats Margarine INGREDIENTS: SOYBEAN OIL, FULLY HYDROGENATED COTTONSEED OIL, PARTIALLY HYDROGENATED COTTONSEED OIL AND SOYBEAN OILS, MONO AND DIGLYCERIDES, TBHO AND CITRIC ACID ANTIOXIDANTS Trans fats Omega-3 fats Plant oils Figure 3.12

  23. Steroids • Steroids are very different from fats in structure and function. • The carbon skeleton is bent to form four fused rings. • Cholesterol is • A key component of cell membranes • The “base steroid” from which your body produces other steroids, such as estrogen and testosterone

  24. Cholesterol Testosterone A type of estrogen Figure 3.13

  25. Synthetic anabolic steroids • Resemble testosterone • Mimic some of its effects • Can cause serious physical and mental problems • Are abused by athletes to enhance performance

  26. Proteins • Proteins • Are polymers constructed from amino acid monomers • Perform most of the tasks the body needs to function • Form enzymes, chemicals that change the rate of a chemical reaction without being changed in the process

  27. MAJOR TYPES OF PROTEINS Contractile Proteins Transport Proteins Enzymes Structural Proteins Storage Proteins Figure 3.15

  28. Proteins as Polymers • Cells link amino acids together by dehydration reactions, forming peptide bonds and creating long chains of amino acids called polypeptides. • The specific sequence of amino acids in a protein is its primary structure.

  29. Amino acids b Secondary structure c Tertiary structure d Quaternary structure a Primary structure Pleated sheet Protein with four polypeptides Polypeptide Alpha helix Figure 3.20-4

  30. What Determines Protein Shape? • A protein’s shape is sensitive to the surrounding environment. • Unfavorable temperature and pH changes can cause denaturation of a protein, in which it unravels and loses its shape. • High fevers (above 104º F) in humans can cause some proteins to denature.

  31. Misfolded proteins are associated with • Alzheimer’s disease • Mad cow disease • Parkinson’s disease

  32. Nucleic Acids • Nucleic acids • Are macromolecules that provide the directions for building proteins • Include DNA and RNA • Are the genetic material that organisms inherit from their parents

  33. DNA resides in cells in long fibers called chromosomes. • A gene is a specific stretch of DNA that programs the amino acid sequence of a polypeptide. • The chemical code of DNA must be translated from “nucleic acid language” to “protein language.”

  34. Gene DNA Nucleic acids RNA Amino acid Protein Figure 3.22

  35. Nucleic acids are polymers of nucleotides. • Each nucleotide has three parts: • A five-carbon sugar • A phosphate group • A nitrogenous base

  36. Each DNA nucleotide has one of the following bases: • Adenine (A) • Guanine (G) • Thymine (T) • Cytosine (C)

  37. Base pair Hydrogen bond b Double helix two polynucleotide strands Figure 3.25b

  38. Two strands of DNA join together to form a doublehelix. • Bases along one DNA strand hydrogen-bond to bases along the other strand. • The functional groups hanging off the base determine which bases pair up: • A only pairs with T. • G can only pair with C.

  39. RNA, ribonucleic acid, is different from DNA. • RNA is usually single-stranded but DNA usually exists as a double helix. • RNA uses the sugar ribose and the base uracil (U) instead of thymine (T).

  40. Large biological molecules Functions Components Examples Monosaccharides: glucose, fructose Disaccharides: lactose, sucrose Polysaccharides: starch, cellulose Dietary energy; storage; plant structure Carbohydrates Monosaccharide Long-term energy storage fats; hormones steroids Fats triglycerides; Steroids testosterone, estrogen Fatty acid Lipids Glycerol Components of a triglyceride Amino group Carboxyl group Lactase an enzyme, hemoglobin a transport protein Enzymes, structure, storage, contraction, transport, and others Proteins Side group Amino acid Phosphate Base Information storage Nucleic acids DNA, RNA Sugar Nucleotide Figure UN3-2

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