Chapter 2 Carbohydrates PDF

Chapter 2 Progress Not started,Not started Content 💡 Definition of Carbohydrates: Carbohydrates, also called saccharides, are chemically defined as polyhydroxyaldehydes (aldoses) or polyhydroxyketones (ketoses). Organic compounds with at least three carbons whereall carbons have a hydroxyl, exc...

Chapter 2 Progress Not started,Not started Content 💡 Definition of Carbohydrates: Carbohydrates, also called saccharides, are chemically defined as polyhydroxyaldehydes (aldoses) or polyhydroxyketones (ketoses). Organic compounds with at least three carbons whereall carbons have a hydroxyl, except for one, which has the primary carbonyl (aldehyde group) or the secondary carbonyl (keto group) Cellular function Energetics – obtaining energy, e.g., glucose, sucrose; - Structural – polymerized or associated with other biomolecules, e.g., cellulose, chitin. - Chemical energy deposit – energy reserve., starch in vegetables, glycogen in animals and fungi, lactose in milk, fructose in fruits and sucrose in sugarcane. - Carbon donor – for the synthesis of other cellular components, e.g., organic acids. Chapter 2 1 Classification Classification (according to the degree of polymerization): - Monosaccharides - single unit of polyhydroxy aldehyde, e.g., glucose. - Oligosaccharides - short chains of monosaccharide units, e.g., sucrose. - Polysaccharides - contains more than 20 monosaccharide units, e.g., cellulose. Saccharide, from the Ancient Greek, sakcharon, means sugar. Classification Classification (according to the degree of polymerization): -Monosaccharides-single unit of polyhydroxyaldehydeor ketone, e.g., glucose; -Oligosaccharides-short chains of monosaccharide units, e.g., sucrose; -Polysaccharides-contains more than 20 monosaccharide units, e.g., cellulose. Saccharide, from the Ancient Greek, sakcharon, means sugar Monosaccharides Monosaccharides are carbohydrates that cannot be broken down by hydrolysis into smaller carbohydrate units. They are also called saccharides and are chemically defined as polyhydroxy aldehydes (aldoses) or polyhydroxy ketones (ketoses), i.e., organic compounds with at least three carbons where all carbons have a hydroxyl, except for one, which has the primary carbonyl (aldehyde group) or the secondary carbonyl (Keto group). Chapter 2 2 A monosaccharide is the most basic form of carbohydrates. It can be combined through glycosidic bonds to form larger carbohydrates, known as oligosaccharides or polysaccharides. An oligosaccharide with only two monosaccharides is known as a disaccharide. Monosaccharides have two broad classifications based on the functional group present in them. If they contain an aldehyde group, they are known as aldose. If they contain a keto group, they are called ketose. Some examples of monosaccharides include glucose and fructose. ketose Ketose is type of monosaccharide containing ketone functional group ketone functional group A ketone is a functional group in organic chemistry that contains a carbonyl group bonded to two carbon atoms. The carbonyl group is a carbon atom double-bonded to an oxygen atom, and the two carbon atoms are bonded to the carbonyl carbon atom ¹. The general formula for a ketone is RC(=O)R', where R and R' can be a variety of carbon-containing substituents. Chapter 2 3 Ketones are classified as a type of carbonyl group, which also includes aldehydes and carboxylic acids. The carbonyl group in ketones is bonded to two carbon atoms, while in aldehydes, it is bonded to one carbon atom and one hydrogen atom. Ketones are important in many biological and industrial processes. They are used in the production of many chemicals, including solvents, plastics, and pharmaceuticals picture carbonyl group surrounded by two carbons Monosaccharides Chapter 2 4 Are the simplest carbohydrates Example: glucose (C6H12O6) C1 – aldose contains- 5 hydroxyl groups (C2-C6), 4 chiral centers (C2C5), Chiral center - carbon atom bonded to four different substituents They are colorless compounds, crystalline solids, soluble in water and insoluble in nonpolar solvents. Types of Monosaccharides, based on the number of carbon molecules Trioses Tetroses Pentoses Hexoses Heptoses 3.1.1Monosaccharide Isomerization Carbon Chiral carbon is a carbon atom within a molecule, typically bonded to four different atoms or groups, leading to mirror-image forms. Dextrose molecule “right sugar” Chain of 6 carbon, with 5 hydroxyl groups (-OH), and 1 aldehyde Group Chapter 2 5 Dextrose, Monosaccharide, Glucose Carbonyl Group Aldehyde 3.1.2Monosaccharide Ring Formation Chapter 2 6 In the context of carbohydrate chemistry, pyranose ring formation occurs when a linear carbohydrate, typically containing an aldehyde or ketone functional group, undergoes a hemiacetal reaction in an aqueous solution. This reaction involves the addition of an alcohol (often a hydroxyl group from another part of the same molecule) to the carbonyl carbon, resulting in the formation of a cyclic hemiacetal structure known as a pyranose ring. Hemiacetal or hemiketals hemia+cet (Cetinje)+al Hemiacetal A hemiacetal is a type of organic compound that results from the addition of an alcohol to an aldehyde or a ketone. It has the general formula R1R2C(OH)OR, where R1 and R2 are hydrogen or an organic substituent . Hemiacetals are intermediates in the reaction between alcohols and aldehydes or ketones, with the final product being an acetal or a ketal. Most sugars are hemiacetals, as are cyclic hemiacetals and hemiketals. picture Chapter 2 7 attaching alcohol to the aldehyde In the context of glucose, the term alcohol refers to the hydroxyl group (−OH) that is attached to the glucose molecule. The hydroxyl group is a functional group that is common in alcohols. In glucose, the hydroxyl group is attached to the carbon atom that is adjacent to the aldehyde group. This carbon atom is known as the anomeric carbon . The hydroxyl group on the anomeric carbon can form a hemiacetal with the aldehyde group, resulting in the formation of a cyclic structure ¹. This cyclic structure is known as a pyranose ring ¹. Hydroxymethyl group C-5 The hydroxymethyl group is a substituent with the structural formula −CH2−OH . It consists of a methylene bridge (−CH2− unit) bonded to a hydroxyl group (−OH) . hydra+ox+methyl, furting bull in the water Chapter 2 8 Pyranose Pyranose ring (pirra nose ring) Chapter 2 9 Haworth projection: hydroxymethyl group and oxygen atom appear to be positioned above Furanose Five member ring, they also occur but are less common than pyranose ring. (fury+nose) Chapter 2 10 3.1.3Glycosides Glycosides are compounds formed by the linkage of a sugar molecule (glycone) to another functional group or compound through a glycosidic bond. Formation of Acetals and Ketals The formation of acetals and ketals involves a reaction between a compound containing a carbonyl group (either an aldehyde or a ketone) and an alcohol. 1. Acetal formation (from aldehydes): a. an aldehyde reacts with an alcohol in the presence of an acid catalyst. b. The carbon oxygen in the aldehyde combines with hydrogen from the alcohol´s hydroxyl groupþ c. This forms a water molecule and creates a new cabon-oxygencarbon linkage, known as acetal. 2. Ketal formation (from ketones): a. a ketone reacts with an alcohol also in the presence of an acid catalyst b. similar to acetal formation, the carbonyl oxygen in the ketone combines with a hydrogen from the alcohol, eliminating water. Chapter 2 11 c. this results in the formation of a new carbon-oxygen-carbon linkage.termed a ketal In both casres the reaction involves the conversion of a carbonyl group into a new functional group called acetal or ketal, respectively, .These reactions are commonly used on organic synthesis for protecting or modifying functional groups in molecules. Glycosidic bond A glycosidic bond is a type of covalent bond that connects a sugar molecule to another compound, typically with the elimination of water. It is formed through a condensation reaction between the anomeric carbon of a sugar (the carbon that is part of the carbonyl group in a sugar) and a hydroxyl group of another molecule. The resulting linkage is called a glycosidic linkage. Glycosidic bonds play a crucial role in the formation of complex carbohydrates, such as disaccharides (e.g., sucrose, lactose) and polysaccharides (e.g., starch, cellulose). The specific type and location of glycosidic bonds determine the structure and properties of these carbohydrates. Disaccharides Formation of maltose Maltose Maltose is a disaccharide composed of two glucose molecules linked by an α(1→4) glycosidic bond. It is commonly referred to as malt sugar and is a product of the enzymatic breakdown of starch, particularly during the germination of grains like barley. Maltose is a reducing sugar, meaning it can participate in chemical reactions that involve the reduction of other substances. In terms of taste, maltose is less sweet compared to some other sugars like sucrose (table sugar). It is often used in the food industry and brewing processes, where it plays a key role in the production of malted beverages such as beer. Reaction Formation of maltose from glucose involves a condensation reaction, specifically a glycosidic bond formation: Chapter 2 12 1. Initial Glucose Molecules: a. start with 2 glucose molecules. Glucose is a monosaccharide, and each molecule has a structure with several carbon atoms. 2. Removal of Water: a. the hydroxyl group (-OH) on the carbon atom at a C1 position of one glucose molecule reacts woth hydroxyl group on the C4 carbon atom of the other glucose molecule b. during this reaction, a water molecule is eliminated. 3. Firmation of Glycosidic Bond: a. the remaining oxygen on the C1 carbon of the first glucose molecule forms a glycosidic bond with the C4 carbon og the second glucose molecule. b. this glycosidic bond is specifically an alpha 1-4 glycosidic linkage 4. Resulting Maltose: a. the product of this condensation reaction is maltose Disaccharides types 1. Lactose 2. Sucrose 3. Trehalose Polysacchaides Frequently classified according to characteristics of their chemical structure Composed of glycosidic units arranged in linear or branched form. Importance: They play an important role in plants and food systems. From the nutritional standpoint, starch is the major polysaccharide and the most digestible in the human intestine. Indigestible polysaccharides also have great importance in health (large intestine, trefjar). Polysaccharides classification Starch Glycogen Chapter 2 13 Cellulose Hemicellulose Pectin Gums Assignments Assignments Name Status Monosaccharides test Not started Notes Not started Notes Notes Name Carbogydrates Chapter 2 Topics Status Not started 14