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SECTION MENU Organic Molecules Organic Molecules: Building Blocks of Life Carbohydrate Structure Lipid Structure Protein Structure Nucleic Acid Structure Main Menu Visualizing Cell Processes Section Vocabulary Section Quiz (&rd Edition) © BioMEDIA ASSOCIATES Organic Molecules: The Building Blocks of Life Organic Molecules Previous Topic Section Menu Main Menu Next Topic Notes: • The carbon atom is the most versatile of all atoms for building molecules. This is due in part to carbon’s tetravalence, or tendancy to make four covalent bonds with other atoms. Carbon atoms bond together to form straight chains, branched chains, or rings – making for an incredible variety of carbon skeletons as the basis for organic molecules. • Narration The molecules that make up living things are all based on carbon. Carbon atoms have four bonding sites. They can bond with hydrogen, in this case, forming the molecule CH4, methane gas. Carbon atoms can also bond with each other, like this. Carbon chains can be combined. An OH from one and an H from another are removed, forming H2O. This is called a condensation reaction. Condensation reactions can assemble building block molecules into long chains of repeating units called polymers. Four kinds of biologically produced polymers play major roles in life: carbohydrates, lipids, proteins and nucleic acids. In a condensation reaction, two molecules become covalently bonded together and a small molecule is lost, usually water. When this covalent bond forms between two monomers, one monomer contributes an OH group and the other a hydrogen, forming H20. To make a polymer, the condensation reaction occurs over and over as each monomer is added to the chain. Condensation reactions are catalyzed by enzymes, and they require energy from the cell. Extensions: • All molecules containing more than one carbon atom are termed organic. Oxygen and hydrogen are found in most organic molecules and nitrogen is also common. Hydrocarbons are organic molecules made only of carbon and hydrogen, such as ethane, or the tail portion of fatty acids. The C-C and C-H bonds in hydrocarbons are non-polar, meaning that electrons are distributed evenly between the two atoms of the bond. • Functional groups add even greater variation to organic molecules. Examples of these are amino, carboxyl, hydroxyl or phosphate groups. Combinations of these bonded to various carbon skeletons form the main organic molecules of life. Visualizing Cell Processes self quiz Water Poster (&rd Edition) © BioMEDIA ASSOCIATES Carbohydrate Structure Organic Molecules Previous Topic • • Narration Sugars are simple carbohydrates. They can be monosaccharides, either straight chains or rings of six carbons; or disaccharides—double sugars. Starch, a polysaccharide, is a complex carbohydrate, made from many sugar molecules. When an animal eats a starch—its digestive enzymes render the polymer back to its building block sugars, ready for absorption. Section Menu Main Menu Next Topic Notes: Carbohydrates include sugars and their polymers. The simplest carbohydrates are monosaccharides, or single sugars. Disaccharides are double sugars formed from two monosaccharides joined by a condensation reaction. Polysaccharides are macromolecule polymers formed from a few to a few thousand monosaccharides joined together. Extensions: Monosaccharides occur in two forms, either as an aldose or a ketose, depending on the location of the carbonyl group (C=0). Sugars are also classified according to the length of the cabon skeleton, which ranges from three to seven carbon atoms, and by the spatial arrangement of their parts. For example, glucose and fructose have the same molecular formula (C 6H 12O6) but differ in the position of the carboxyl group. Monosaccharides are a major food source for cells. Sugar molecules also act as raw material for building other organic molecules, such as amino acids. • Disaccharides, such as maltose, lactose and sucrose, are two-unit polymers of monosaccarides joined with a glycosidic linkage. Sucrose, table sugar, is a disaccharide common in nature. It is used by plants to transport food energy from leaves to roots. • Polysaccharides are divided into two groups, storage polysaccharides and structural polysaccharides . In plants and animals, starch and glycogen are storage polysaccharides. Cellulose and chitin are strucutral polysaccharides. Polysaccharides are usually made from glucose (or modified-glucose) monomers. Hydrolysis of storage polysaccharides releases glucose, a major cellular fuel source. self quiz Visualizing Cell Processes Web Link ORG 01 (&rd Edition) © BioMEDIA ASSOCIATES Lipid Structure Organic Molecules Previous Topic Section Menu Main Menu Next Topic Notes: • There are three groups of lipids: fats, phospholipids and steroids. Fats are made of glycerol and fatty acids. Fatty acids have hydrocarbon chain ‘tails’ consisting of 16 or 18 carbons with a carboxyl group ‘head’. A triglyceride (a fat) results when three fatty acids bond to a glycerol with ester linkages. • Plasma membranes rely on the mix of hydrophobic and hydrophilic properties of phospholipids to maintain stability and flexibility. Steroids, including cholesterol, have a carbon skeleton made of four interconnected rings with a variety of functional groups attached to the rings. Cholesterol is a key starting molecule for the biochemical synthesis of most other steroids. Narration Lipids are made of short carbon chains called fatty acids. The plasma membrane is a double layer of phospholipids composed of two fatty acids attached to a phosphate containing “head”. These “heads” are “hydrophilic (attracted to water) so in water they orient like this—heads pointing out. The tails are hydrophobic and so point in. This orientation to water is responsible for the typical bilayer configuration of all cell membranes. Another lipid configuration has three fatty acids combined with a glycerol—a triglyceride—the energy storing fat produced by animals. A third type of lipid, cholesterol, is found in membranes and is used by cells for synthesizing certain steroid hormones. Extensions: • The major function of fats is energy storage. Since fats store twice as much energy as carbohydrates, they represent a much more efficient storage molecule. In general, animals store energy as fats, while plants, being non-motile, are able to survive by storing energy as starch. Animals store fats in adipose cells, which swell and shrink as fat reserves go up and down. • Fatty acids can be saturated or unsaturated. A saturated fatty acid has no double bonds between carbon atoms in the hydrocarbon tails. An unsaturated fatty acid can have one or more double bonds between carbon atoms in the tails. A fatty acid will have a kink wherever a double bond occurs. Visualizing Cell Processes self quiz Web Link ORG 02 Web Link ORG 03 (rd Edition) © BioMEDIA ASSOCIATES Organic Molecules Protein Structure Previous Topic • • Narration Fats and carbohydrates are basically chains of similar building block molecules. Proteins are also polymers, but are made from 20 different amino acid building blocks. Condensation reactions can fit amino acids together in any combination. Section Menu Main Menu Next Topic Notes: Based on combining twenty amino acid building blocks, nature has formed millions of different kinds of proteins. Proteins are used for structural support, storage, transport of substances, signalling within an organism, movement and defence. Some proteins are enzymes that accelerate chemical reactions, thereby regulating an organism’s metabolism and other biochemical activities. Enzyme Poster Extensions: Every amino acid has a central carbon atom bonded to four things: 1) a hydrogen atom, 2) a carboxyl group 3) an amino group, and 4) a side group, or ‘R group’. The twenty amino acids in proteins differ from each other only at the side (R) group. Physical and chemical properties of the side group determine characteristics of the amino acid. For example, side groups can be polar, non-polar or electrically charged. Amino Acid Table • Amino acid building blocks inside a protein are called peptides, and a chain of peptides is a polypeptide. Condensation reactions between amino acids create peptide bonds. The peptide bond links the carboxyl group of one amino acid to the amino group of its neighbor. • Proteins are usually made from two or more polypeptide chains. They have four levels of structure: primary structure is the amino acid sequence in a polypeptide; secondary structure results from simple folding and coiling of the polypeptide units; tertiary structure involves further folding; and quarternary structure results from linking (2-many) polypeptides together. The result is a unique conformation for each protein that contributes to its individual function. self quiz Visualizing Cell Processes Web Link ORG 04 (&rd Edition) © BioMEDIA ASSOCIATES Nucleic Acid Structure Organic Molecules Previous Topic Section Menu Main Menu Next Topic Notes: • Nucleic acids are polymers made of nucleotide building blocks. Two types of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are essential for the cell. DNA stores the genetic code, while several types of RNA are involved with the transfer of genetic information and building of proteins. Extensions: • Nucleotides consists of three parts: a phosphate group, a pentose sugar and a nitrogenous base. In DNA, the sugar is deoxyribose. In RNA, the sugar is ribose. Narration Nucleic acids are polymers made from four kinds of building block nucleotides. DNA is an extremely long molecule composed of two strands wound in a double helix. Each strand is made up of a chain of nucleotides. Nucleotides have a common structure – a phosphate group, a sugar and a nitrogenous base unit. There are four kinds of nitrogenous bases – thymine, guanine, cytosine and adenine. • There are two families of nitrogenous bases, pyrimidines and purines. Pyrimidines have a six-membered ring. Pyrimidines include: cytosine (C) (in DNA and RNA), thymine (T)(only in DNA), and uracil (U)(only in RNA). The purines adenine (A) and guanine (G) are larger with a six-membered ring attached to a five-membered ring. • In DNA, covalent bonds join the phosphate group of one nucleotide to the sugar of its neighbor. This results in an alternating phosphate-sugar backbone. Each strand of DNA has a unique sequence of bases attached to this phosphate-sugar backbone. • Two complementary DNA strands form a double helix, and this is the normal form of DNA in the cell. Genes, the unit of inheritance, are made of DNA. The coding capabilities of DNA result from the arrangement of base sequences on the DNA strands. self quiz Visualizing Cell Processes Web Link ORG 05 (rd Edition) © BioMEDIA ASSOCIATES