Brown Hair, Blue Eyes, and Big Mice • The study of genes has increased our understanding of how we think, how we behave, and what diseases we might have a genetic predisposition to develop. • We understand not only how a molecular sequence works, but how to take it from one organism and implant it in another. • Four types of molecules in living organisms • Lipids • Carbohydrates • Proteins • Nucleic acids a lipid
Lipids and Fats • Lipids are cellular components that are insoluble in water, but extractable in nonpolar solvents. • Fats, oils, fatty acids, steroids, and some vitamins • They form the structural components of biological membranes and reservoirs for long-term energy storage. • They contain twice as much energy per gram as any other class of biochemical compounds. • Efficient energy storage
Fatty Acids • One type of lipid • Organic acid with a long hydrocarbon tail • General formula RCOOH
Triglycerides • Fats and oils are a chemical combination of glycerol and three fatty acids.
Tristearin • Structure/property relationships • Long hydrocarbon chains: Nonpolar, immiscible with water • Energy is extracted via oxidation of these long chains (as in gasoline). • Chains are saturated: Efficient packing, solids • Fat is conveniently stored in the body. • Provides thermal insulation
Triolein • Main component of olive oil • Double bonds in R groups interfere with efficient packing, lowering the melting point and making it a liquid at room temperature.
Trilinolenin • Polyunsaturated fat: Multiple double bonds in the hydrocarbon chains • Animal fats tend to be saturated. • Plant fats tend to be unsaturated. • Variations in structure serve different purposes in the human body.
Concept Check 16.1 • What is the difference between fats/oils and fatty acids.
Concept Check 16.1 Solution • Fatty acids are components of fats. Fats are triglycerides (glycerol triesters) of three fatty acids (long chain carboxylic acids greater than 12 carbons).
Concept Check 16.2 • Which of the following two triglycerides is expected to be a liquid at room temperature?
Concept Check 16.2 Solution • Triglyceride (b) is an unsaturated fat, therefore, expected to be a liquid at room temperature. • Saturated fats are solids at room temperature.
Carbohydrates • Chemical formulas are multiples of CH2O (carbon-carbo and water-hydrate). • Function in the body as short-term energy storage • Chemical structure related to: • Carbohydrates are polyhydroxy aldehydes, or ketones, or their derivatives.
Glucose • This is a dynamic system, but at any instant more molecules are in the ring form than in the linear form. The formation of a six-membered ring occurs between the —OH at C5 reacting with the aldehyde carbon, C1.
Glucose Properties • Hydroxyl groups mean strong hydrogen bonding with each other and with water. • Solubility in body fluids leads to function as a quick energy source. • Since it is partially oxidized, it yields less energy per gram than octane or lipids of similar carbon content. • Balance between efficient energy storage and ease of access to that energy
Fructose versus Glucose • Isomer of glucose; a five-membered ring • Two CH2OH groups mean it is more soluble in water and sweeter. • Takes less fructose to achieve the same sweetness as glucose
Concept Check 16.3 • Which of the following structures are carbohydrates?
Concept Check 16.3 Solution • Structures (a) and (c) are carbohydrates. They have formulas of the form Cx(H2O)y.
Saccharides • Monosaccharides: Carbohydrates composed of a single ring • Disaccharides: Two monosaccharide rings connected to form a single structure.
Saccharides • Monosaccharide units building a polysaccharide (complex carbohydrate
Complex Carbohydrates • Polysaccharides (complex carbohydrates) • Most common are starch and cellulose • Subtle molecular difference (the oxygen linkage between rings and subsequent nature of resulting hydrogen bonds) means a dramatic macroscopic result. • Human enzymes cannot break the bonds between glucose rings. Intramolecular hydrogen bonds in cellulose prevent hydrogen bonding with water.
Concept Check 16.4 • Classify each of the following carbohydrates as a monosaccharide, disaccharide, or polysaccharide.
Concept Check 16.4 Solution • Compounds (a) and (d) are carbohydrates in their monocyclic form. Carbohydrate (b) has two linked monosaccharide rings. Carbohydrate (c) has many repeating monosaccharide rings.
The body CAN metabolize proteins. The body metabolizes proteins ONLY as a last resort. Proteins have much more important other work to do in the body. Proteins
Protein Functions • Compose much of the physical structure of the body (muscle, hair, skin) • Act as enzymes to control chemical reactions • Act as hormones to regulate metabolic processes • Transport oxygen from lungs to cells • Act as antibodies
Protein Functions Protein molecules are long chains of amino acids. Differences among amino acids arise from different R groups. Amino acids are molecules that contain both an amine group and a carboxylic acid group. There are only 20 common amino acids. Changing the number and order of these amino acids changes the functionality of the protein. The simplest R group is the hydrogen atom; the amino acid is glycine.
Concept Check 16.5 • Which of the following molecules are amino acids?
Concept Check 16.5 Solution • Amino acids have the general structure, where the amino and carboxyl groups are attached to the samecarbon: • Compounds (b) and (d) are amino acids.
The Peptide Bond • The acidic end of one amino acid reacts with the amine side of another to form a peptide bond. • Two linked amino acids is called a dipeptide. • Chains with 50 units or less are polypeptides; chains with over 50 units are called proteins.
Concept Check 16.6 • Draw the tripeptide that results from a cysteine in the middle with an alanine on each side.
Concept Check 16.6 Solution • The tripeptide is built as follows: • The formation of the peptide bond is a condensation reaction (See Chapter 15).
Sickle Cell Anemia • Hemoglobin (Hb) is a medium-size protein with a molecular formula that contains close to 10,000 atoms: C2952H4664O832S8Fe4 • Replacing polar glutamate with nonpolar valine at one position on two of these chains lowers the solubility of Hb, resulting in red blood cell deformation. The deformed blood cells block the flow of blood to capillaries.
Protein Structure • The structure of a protein is finely tuned to achieve a specific function. • We characterize protein structure in four categories: • Primary • Secondary • Tertiary • Quaternary
Primary Structure • The amino acid sequence held together by peptide bonds • Abbreviations like “Gly-Val-Ala-Asp” are used to describe the sequence of the amino acids.
The way the amino acid chain orients itself along its axis Common secondary structures Alpha-helix Pleated sheet Secondary Structure
Alpha-Helix • Helical shape is maintained by hydrogen bonds between different amino acids along the protein chain. • α-keratin is an alpha-helix and is responsible for the elasticity of hair and wool. • It works like a spring.
Protein forms zigzag chains that stack neatly together. Silk is a pleated sheet Inelasticity due to full extension of protein chains Softness due to sliding of sheets past each other Pleated Sheet
Tertiary and Quaternary Structures • Tertiary structure is the bending and folding due to interactions between amino acids on the chain. • Completely extended • Globular or ball-like • Overall shape of the particular protein strand • The arrangement of subunits of the protein chain in space is the quaternary structure.
Interactions Responsible for Protein Tertiary and Quaternary Structure The tertiary and quaternary structures of proteins are maintained by four kinds of interactions between R groups on different parts of the protein strand: • Hydrogen bonding • Hydrophobic interactions • Salt bridges • Disulfide linkages
Common Proteins: Hemoglobin (Hb) • Entire structure not known until late 1950s • Hb folds to hold four flat molecules called heme groups. • Picks up oxygen at lungs • Releases it at cells undergoing glucose oxidation • Interior of Hb molecule is highly nonpolar. • Repels water • Allows oxygen in and out • Exterior is polar • Hemoglobin is soluble in water.
α-Keratin • Composes hair and wool • α-helix structure maintained by hydrogen bonding • Hair • Three α-helices in a coil held together by hydrogen bonds and disulfide linkages, which upon chemical treatment can easily break and reform.
Acts as an enzyme Cleaves polysaccharide units within cell walls Walls explode, killing the bacteria Found in nasal mucus and tears Discovered by Alexander Fleming in 1922 Lysozyme
Acts as a hormone Synthesized in the pancreas Small (51 amino acids) Promotes entry of glucose into muscle and fat cells, lowering blood glucose level Diabetics may have to inject insulin. Insulin
Nucleic Acids • The templates from which all proteins are made • Two types • DNA (deoxyribonucleic acid) • Occurs primarily in the cell information center (nucleus) • RNA (ribonucleic acid) • Occurs throughout interior of cells
Nucleotides • Phosphate and sugar groups are identical in every nucleotide, the monomer of nucleic acids. • Four different bases • A, adenine • T, thymine • C, cytosine • G, guanine • Codon • A group of three bases that codes for one amino acid • With minor exceptions, the code is universal; it is identical in all organisms, from bacteria to humans.
DNA • Occurs in chromosomes, found in the nucleus of most cells of the human body • There are 46 chromosomes in humans. • Each set of DNA contains all the DNA required to specify an entire person. • Organs make those proteins specific for their own functioning. • The blueprint is there in each cell with a nucleus for everything else too.
DNA Replication • Mechanism elucidated by Watson, Crick, and Franklin in 1953 • Complementary base units are formed (with the help of enzymes) after the double-helix unzips. • Two daughter DNA strands formed • Daughter DNA molecules are identical in every way to the parent. A pairs with T C pairs with G
Concept Check 16.7 • Draw the complementary strand for the DNA shown.
Concept Check 16.7 Solution • In the complementary strand, adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G).