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Chapter 3 Biological Molecules Lecture Outlines by Gregory Ahearn, University of North Florida Copyright © 2011 Pearson Education Inc. Chapter 3 At a Glance 3.1 Why Is Carbon So Important in Biological Molecules? 3.2 How Are Organic Molecules Synthesized? 3.3 What Are Carbohydrates? 3.4 What Are Lipids? 3.5 What Are Proteins? 3.6 What Are Nucleotides and Nucleic Acids? Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.1 Why Is Carbon So Important in Biological Molecules? Organic/inorganic molecules and functional groups – Organic refers to molecules containing a carbon skeleton bonded to hydrogen atoms – Inorganic refers to carbon dioxide and all molecules without carbon Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.1 Why Is Carbon So Important in Biological Molecules? Organic/inorganic molecules and functional groups (continued) – The carbon atom is versatile because it has four electrons in an outermost shell that can accommodate eight electrons – Therefore, a carbon atom can become stable by forming up to four bonds (single, double, or triple) – As a result, organic molecules can assume complex shapes, including branched chains, rings, sheets, and helices Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.1 Why Is Carbon So Important in Biological Molecules? Functional groups in organic molecules determine the characteristics and chemical reactivity of the molecules – Functional groups are less stable than the carbon backbone and are more likely to participate in chemical reactions Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Table 3-1 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.2 How Are Organic Molecules Synthesized? – Small organic molecules (called monomers) are joined to form longer molecules (called polymers) – Biomolecules are joined or broken through dehydration synthesis or hydrolysis Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.2 How Are Organic Molecules Synthesized? Monomers are joined together through dehydration synthesis, at the site where an H and an OH are removed, resulting in the loss of a water molecule (H2O) The openings in the outer electron shells of the two subunits are filled when the two subunits share electrons, creating a covalent bond Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Author Animation: Monomers and Polymers Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Dehydration Synthesis dehydration synthesis Fig. 3-1 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.2 How Are Organic Molecules Synthesized? Polymers are broken apart through hydrolysis (“water cutting”) – Water is broken into H and OH and is used to break the bond between monomers Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Author Animation: Hydrolysis Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Hydrolysis hydrolysis Fig. 3-2 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.2 How Are Organic Molecules Synthesized? All biological molecules fall into one of four categories – Carbohydrates – Lipids – Proteins – Nucleotides/nucleic acids Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Table 3-2 (1 of 2) Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Table 3-2 (2 of 2) Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.3 What Are Carbohydrates? Carbohydrate molecules are composed of C, H, and O in the ratio of 1:2:1 – If a carbohydrate consists of just one sugar molecule, it is a monosaccharide – Two linked monosaccharides form a disaccharide – A polymer of many monosaccharides is a polysaccharide Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.3 What Are Carbohydrates? Carbohydrates are important energy sources for most organisms Most small carbohydrates are water-soluble due to the polar OH functional group Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.3 What Are Carbohydrates? There are several monosaccharides with slightly different structures – The basic monosaccharide structure is: – A backbone of 3–7 carbon atoms – Most of the carbon atoms have both a hydrogen (-H) and an hydroxyl group (-OH) attached to them – Most carbohydrates have the approximate chemical formula (CH2O)n where “n” is the number of carbons in the backbone – When dissolved in the cytoplasmic fluid of a cell, the carbon backbone usually forms a ring Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.3 What Are Carbohydrates? There are several monosaccharides with slightly different structures (continued) – Example monosaccharides –Glucose (C6H12O6): the most common Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.3 What Are Carbohydrates? Glucose (C6H12O6) is the most common monosaccharide in living organisms – Sugar dissolving in water water hydrogen bond hydroxyl group Fig. 3-3 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.3 What Are Carbohydrates? Additional monosaccharides are: – Fructose (“fruit sugar” found in fruits, corn syrup, and honey) – Galactose (“milk sugar” found in lactose) – Ribose and deoxyribose (found in RNA and DNA, respectively) Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Monosaccharides 6 6 5 2 5 4 3 1 fructose 4 1 3 2 galactose Fig. 3-5 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Ribose Sugars 5 5 4 1 3 2 ribose 4 1 3 2 Note “missing” oxygen atom deoxyribose Fig. 3-6 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.3 What Are Carbohydrates? There are several monosaccharides with slightly different structures (continued) – The fate of monosaccharides inside a cell is: –Some are broken down to free their chemical energy –Some are linked together by dehydration synthesis Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.3 What Are Carbohydrates? Disaccharides consist of two monosaccharides linked by dehydration synthesis – Disaccharides are two-part sugars –They are used for short-term energy storage –When energy is required, they are broken apart into their monosaccharide subunits by hydroysis Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Synthesis of a Disaccharide glucose sucrose fructose • dehydration synthesis • Fig. 3-7 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.3 What Are Carbohydrates? Examples of disaccharides include: – Sucrose (table sugar) = glucose + fructose – Lactose (milk sugar) = glucose + galactose – Maltose (malt sugar) = glucose + glucose Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.3 What Are Carbohydrates? Polysaccharides are chains of simple sugars – Storage polysaccharides include: –Starch, an energy-storage molecule in plants, formed in roots and seeds –Glycogen, an energy-storage molecule in animals, found in the liver and muscles – Both starch and glycogen are polymers of glucose molecules Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Starch is an Energy-Storing Plant Polysaccharide starch grains (a) Potato cells (b) A starch molecule (c) Detail of a starch molecule Fig. 3-8 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.3 What Are Carbohydrates? Polysaccharides are chains of simple sugars (continued) – Many organisms use polysaccharides as a structural material – Cellulose (a polymer of glucose) is one of the most important structural polysaccharides –It is found in the cell walls of plants –It is indigestible for most animals due to the orientation of the bonds between glucose molecules Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Author Animation: Carbohydrate Structure and Function Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Cellulose Structure and Function Fig. 3-9 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.3 What Are Carbohydrates? Polysaccharides are chains of simple sugars (continued) – Chitin (a polymer of modified glucose units) is found in: –The outer coverings of insects, crabs, and spiders –The cell walls of many fungi Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Chitin: A Unique Polysaccharide Fig. 3-10 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.4 What Are Lipids? Lipids are a diverse group of molecules that contain regions composed almost entirely of hydrogen and carbon – All lipids contain large chains of nonpolar hydrocarbons – Most lipids are therefore hydrophobic and water insoluble Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Author Animation: Lipids Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.4 What Are Lipids? Lipids are diverse in structure and serve a variety of functions – They are used for energy storage – They form waterproof coverings on plant and animal bodies – They serve as the primary component of cellular membranes – Still others are hormones Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Lipids in Nature: Fat Fig. 3-11a Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.4 What Are Lipids? Lipids are classified into three major groups – Oils, fats, and waxes – Phospholipids – Steroids containing rings of carbon, hydrogen, and oxygen Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.4 What Are Lipids? Oils, fats, and waxes – Oils, fats, and waxes are made of one or more fatty acid subunits – Fats and oils –Are used primarily as energy-storage molecules, containing twice as many calories per gram as carbyhydrates and proteins –Are formed by dehydration synthesis –Three fatty acids + glycerol triglyceride Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Synthesis of a Triglyceride glycerol fatty acids triglyceride Fig. 3-12 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.4 What Are Lipids? Oils, fats, and waxes (continued) – Fats that are solid at room temperature are saturated (the carbon chain has as many hydrogen atoms as possible, and mostly or all CC bonds); for example, beef fat Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. A Fat Fig. 3-13a Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.4 What Are Lipids? Oils, fats, and waxes (continued) – Fats that are liquid at room temperature are unsaturated (with fewer hydrogen atoms, and many C=C bonds); for example, corn oil –Unsaturated trans fats have been linked to heart disease Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Author Animation: Triglycerides Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. An Oil Fig. 3-13b Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.4 What Are Lipids? Oils, fats, and waxes (continued) – Waxes are highly saturated and solid at room temperature Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.4 What Are Lipids? Oils, fats, and waxes (continued) – Waxes form waterproof coatings such as on: –Leaves and stems in plants –Fur in mammals –Insect exoskeletons – Waxes are also used to build honeycomb structures Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Lipids in Nature: Wax Fig. 3-11b Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.4 What Are Lipids? Phospholipids – These form plasma membranes around all cells – Phospholipids consist of two fatty acids + glycerol + a short polar functional group – They have hydrophobic and hydrophilic portions –The polar functional groups form the “head” and are water-soluble –The nonpolar fatty acids form the “tails” and are water insoluble Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Author Animation: Phospholipids Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Phospholipids variable functional phosphate group group polar head (hydrophilic) glycerol backbone fatty acid tails (hydrophobic) Fig. 3-14 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.4 What Are Lipids? Steroids – Steroids are composed of four carbon rings fused together with various functional groups protruding from them – Examples of steroids include: –Cholesterol –Found in the membranes of animal cells –Male and female sex hormones Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Author Animation: Steroids Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Steroids Fig. 3-15 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.5 What Are Proteins? Functions of proteins – Proteins have a variety of functions –Enzymes are proteins that promote chemical reactions –Structural proteins (e.g., elastin) provide support Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Structural Proteins Fig. 3-16 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.5 What Are Proteins? Proteins are formed from chains of amino acids joined by peptide bonds – All amino acids have a similar structure –All contain amino and carboxyl groups –All have a variable “R” group –Some R groups are hydrophobic –Some are hydrophilic –Cysteine R groups can form disulfide bridges Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Amino Acid Structure variable group amino group carboxylic acid group hydrogen Fig. 3-17 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Amino Acid Diversity glutamic acid (glu) aspartic acid (asp) (a) Hydrophilic functional groups phenylalanine (phe) leucine (leu) (b) Hydrophobic functional groups cysteine (cys) (c) Sulfur-containing functional group Biology: Life on Earth, 9e Fig. 3-18 Copyright © 2011 Pearson Education Inc. 3.5 What Are Proteins? The sequence of amino acids in a protein dictates its function Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.5 What Are Proteins? Amino acids are joined to form chains by dehydration synthesis – An amino group reacts with a carboxyl group, and water is lost Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Protein Synthesis amino acid amino acid dehydration synthesis • amino group carboxylic acid group water peptide amino group peptide bond Fig. 3-19 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.5 What Are Proteins? Amino acids are joined to form chains by dehydration synthesis (continued) – The covalent bond resulting after the water is lost is a peptide bond, and the resulting chain of two amino acids is called a peptide – Long chains of amino acids are known as polypeptides, or just proteins Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.5 What Are Proteins? Proteins exhibit up to four levels of structure – Primary structure is the sequence of amino acids linked together in a protein – Secondary structure is a helix, or a pleated sheet – Tertiary structure refers to complex foldings of the protein chain held together by disulfide bridges, hydrophobic/hydrophilic interactions, and other bonds – Quaternary structure occurs where multiple protein chains are linked together Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Author Animation: Protein Structure Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Four Levels of Protein Structure (b) Secondary structure: Usually maintained by hydrogen bonds, which shape this helix (a) Primary structure: The sequence of amino acids linked by peptide bonds leu val heme group lys lys gly his hydrogen ala bond lys val lys helix pro (c) Tertiary structure: Folding of the helix results from hydrogen bonds with surrounding water molecules and disulfide bridges between cysteine amino acids (d) Quaternary structure: Individual polypeptides are linked to one another by hydrogen bonds or disulfide bridges Fig. 3-20 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Pleated Sheet: An Example of Secondary Structure hydrogen bond pleated sheet Biology: Life on Earth, 9e Fig. 3-21 Copyright © 2011 Pearson Education Inc. 3.5 What Are Proteins? The functions of proteins are linked to their three-dimensional structures – Precise positioning of amino acid R groups leads to bonds that determine secondary and tertiary structure – Disruption of secondary and tertiary bonds leads to denatured proteins and loss of function Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.6 What Are Nucleic Acids? Nucleotides act as energy carriers and intracellular messengers – Nucleotides are the monomers of nucleic acid chains – All nucleotides are made of three parts: –Phosphate group –Five-carbon sugar –Nitrogen-containing base Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Deoxyribose Nucleotide phosphate base sugar Biology: Life on Earth, 9e Fig. 3-22 Copyright © 2011 Pearson Education Inc. 3.6 What Are Nucleic Acids? Nucleotides act as energy carriers and intracellular messengers (continued) – Adenosine triphosphate (ATP) is a deoxyribose nucleotide with three phosphate functional groups Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. The Energy-Carrier Molecule Adenosine Triphosphate (ATP) Fig. 3-23 Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.6 What Are Nucleic Acids? DNA and RNA, the molecules of heredity, are nucleic acids – There are two types of polymers of nucleic acids –DNA (deoxyribonucleic acid) is found in chromosomes and carries genetic information needed for protein construction –RNA (ribonucleic acid) makes copies of DNA and is used directly in the synthesis of proteins Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. 3.6 What Are Nucleic Acids? Each DNA molecule consists of two chains of nucleotides that form a double helix linked by hydrogen bonds Biology: Life on Earth, 9e Copyright © 2011 Pearson Education Inc. Deoxyribonucleic Acid hydrogen bond Biology: Life on Earth, 9e Fig. 3-24 Copyright © 2011 Pearson Education Inc.