Carbohydrates, Proteins and Lipids Unit IV Carbohydrates, Proteins and Lipids

Objectives: Describe the chemical composition and general structure of carbohydrates. Describe three classes of carbohydrates, how they are synthesized, specific examples of each (name, empirical and structural formulas) and their functions. Define and describe examples of monosaccharide isomers Describe the chemical composition and structures of lipids Describe the formation of a triglyceride Compare and contrast saturated and unsaturated triglycerides List and describe examples of various forms of lipids and their functions in living things. Describe the chemical composition of proteins Describe the general structure of an amino acid and the variation of amino acids (how many, how are they similar, how they are different) Describe the formation of peptide bonds and how polypeptide chains are formed. Describe the 4 levels of protein structure. Describe the major functions of proteins. Describe the function, structure, and formation of nucleic acids.

Classes of Carbohydrates There are three major classes of carbohydrates: 1. Monosaccharides (simple sugars) These are the monomers or building blocks for all other classes of carbohydrates. Examples: glucose, fructose, galactose, and ribose. 2. Disaccharides are produced by joining two simple sugars by dehydration synthesis forming a covalent bond between them. Examples: sucrose (table sugar), maltose, lactose 3. Polysaccharides (complex carbohydrates) are produced by joining many monosaccharides together by many dehydration synthesis reactions forming a polymer molecule. Examples: amylose, glycogen, cellulose, and chitin

Carbohydrates Most carbohydrates end with the suffix -ose All carbohydrates are composed of carbon, hydrogen, and oxygen in a 1:2:1 empirical ratio. The general empirical formula for a carbohydrate is CH2O. If a carbohydrate has 5 carbons atoms, what would be its empirical formula? If a carbohydrate has 12 hydrogen atoms present, what would be its empirical formula? Most carbohydrates end with the suffix -ose C5H10O5 C6H12O6

Functions of Carbohydrates Provide energy source: A fuel source when catabolized during cellular respiration. Energy is stored in the chemical bonds within the molecule and released during cellular respiration. Usually simple sugars. Provide energy storage: Plants store energy in a complex carbohydrate form called starch (amylose). Animals store energy in a complex carbohydrate in their muscle tissue and liver in the called glycogen. Structural Building Material: Plants build their cell walls of a complex carbohydrate material called cellulose. Animals such as arthropods build their exoskeletons of a complex carbohydrate called chitin. Chitin is also found in the cell walls of Fungi.

Monosaccharides (Simple sugars) They may exist in a linear molecule or in ring forms. They are classified according to the number of carbon atoms in their molecule. 5 carbons are called pentoses ex. Ribose 6 carbons are called hexoses ex. Glucose Many forms exists as isomers. Isomers are molecules which have the same empirical formula (recipe) but have different structures (shapes) due to arrangement of the atoms in the molecule. This also gives them different properties. Glucose and fructose both have the empirical formula C6H12O6, but they have different structural formulas or shapes. MONOSACCHARIDES ARE THE BUILDING BLOCKS FOR ALL OTHER CARBOHYDRATES!

Monosaccharide Isomers H—C—OH C O H H H C C OH H OH C C OH H OH H H—C—OH O H C C OH OH H C C H OH α- GLUCOSE FRUCTOSE What is the empirical formula for these molecules? C6H12O6

Monomer called Glucose This is dehydration synthesis. During this type of reaction, a water molecule is removed (an –OH from one simple monomer and an –H from another to form a water molecule. This joins two monomers together to form a polymer. When adding another monomer to the dimer, another water molecule needs to be removed. Monomer called Glucose Dimer called Maltose

Functional Groups

Disaccharide Formation and Structure Disaccharides are formed when two monosaccharides are joined by dehydration synthesis. CH2OH H O H OH OH CH2OH H O H HO OH CH2OH H O H OH O H20 + α- GLUCOSE α- GLUCOSE MALTOSE

Polysaccharide Structure and Formation Polysaccharides are chains of monosaccharides that have been joined by many dehydration synthesis reactions. The function of the polysaccharide depends on what type of isomer of glucose the polysaccharide is made. This determines how the glucose molecules bond together (linkage) and whether they can be used for energy storage or structural molecules.

Alpha and Beta Glucose and Their 1,4 Linkages are structural isomers. They differ only in the location of the hydrogen and hydroxl group location on carbon 1.

Alpha linkage, the bond produced when alpha glucose produces a polysaccharide, can be broken by enzymes present in plants and animals. In other words, it can be metabolized. (energy storage) Beta linkage can not be broken by enzymes present in plants and animal, therefore it can not be metabolized. (structural)

Storage Polysaccharides Starch and glycogen both have alpha 1,4 linkage and form helical chains that are often highly branched. The diagram to the left show starch or amylose granules in a chloroplast of a plant cell. The diagram to the left shows glycogen granules in a liver section of an animal. Glycogen is usually more highly branched than amylose.

Structural Polysaccharides Chitin is the “plastic-like” material that composes the exoskeletons of arthropods (insects, arachnids, and crustaceans). Most fungi (mushrooms) have chitin present within their cell walls. Above is a structural monomer of chitin.