Carbohydrates PDF

Carbohydrates:  Carbohydrates Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically in the ratio Cm(H2O)n usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) They are vital biological macromolecules found in all living organisms, ser...

Carbohydrates:  Carbohydrates Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically in the ratio Cm(H2O)n usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) They are vital biological macromolecules found in all living organisms, serving as a primary source of energy, structural components, and involvement in various biochemical processes. The term "carbohydrate" comes from their general formula, which suggests they are hydrates of carbon. Carbohydrates play crucial roles in cellular functions, including energy storage, signaling, and as building blocks for more complex molecules. General Properties of Carbohydrates Carbohydrates are organic compounds composed of carbon (C), hydrogen (H), and oxygen (O), typically in a 1:2:1 ratio (Cₙ(H₂O)ₙ). They are one of the four main macromolecules essential for life and are known for their diverse biological functions, including energy storage, structural roles, and signaling. Chemical Composition and Structure Isomerism Solubility Taste Optical Activity Reducing Properties Polymer Formation Energy Source Immediate Energy: Monosaccharides like glucose are quickly metabolized to produce energy in the form of ATP during cellular respiration. Storage: Polysaccharides like starch (in plants) and glycogen (in animals) serve as long-term energy storage molecules. These polysaccharides can be broken down into glucose when energy is needed. Caloric Value: Carbohydrates provide 4 kcal/gram of energy, making them a significant part of the human diet. Structural Role Structural Polysaccharides: Certain polysaccharides serve as structural components in living organisms. For example: o Cellulose: A major component of plant cell walls, providing rigidity and strength. It consists of β-D- glucose units linked by β-1,4-glycosidic bonds, which humans cannot digest due to a lack of cellulase enzymes. o Chitin: Found in the exoskeletons of arthropods and the cell walls of fungi, chitin is a modified polysaccharide that provides structural support. Biological Functions Energy Storage: Carbohydrates are stored in the form of glycogen in animals and starch in plants, both of which can be broken down to glucose to provide energy. Cell Communication: Oligosaccharides on the surface of cells play roles in cell signaling and recognition. Glycoproteins and glycolipids in the cell membrane have carbohydrate moieties that are involved in interactions with other cells or the extracellular matrix. Protection: Mucopolysaccharides (e.g., hyaluronic acid) contribute to tissue lubrication and protection, particularly in joints and the extracellular matrix. Classification of Carbohydrates Carbohydrates are classified based on the number of sugar units and the complexity of their structure. The major types are: 1. Monosaccharides These are the simplest carbohydrates, consisting of a single sugar unit. Examples include: o Glucose (C₆H₁₂O₆) o Fructose o Galactose Structure of Carbohydrates Carbohydrates consist of hydroxyl groups (-OH) attached to carbon atoms, and an aldehyde (-CHO) or ketone (C=O) group depending on the type of sugar. Monosaccharides The structure of monosaccharides is based on the number of carbon atoms: o Trioses (3 carbons, e.g., glyceraldehyde) o Pentoses (5 carbons, e.g., ribose) o Hexoses (6 carbons, e.g., glucose) Monosaccharides can exist in linear or cyclic forms. In aqueous solutions, they often form rings, where the carbonyl group reacts with a hydroxyl group, resulting in a hemiacetal or hemiketal structure. Disaccharides Formed by the linkage of two monosaccharides via a glycosidic bond. Common examples are: o Sucrose (Glucose + Fructose) o Lactose (Glucose + Galactose) o Maltose (Glucose + Glucose) Disaccharides form when two monosaccharides are linked by a glycosidic bond between their hydroxyl groups. The bond can be alpha (α) or beta (β) depending on the orientation of the hydroxyl group. Oligosaccharides Composed of 3-10 monosaccharide units. They are often found attached to proteins and lipids, playing roles in cell recognition and signaling.  Polysaccharides Polysaccharides can be linear, like cellulose, or highly branched, like glycogen. The type of glycosidic bonds (α or β) determines the function and digestibility. For example, humans can digest starch (α-1,4 and α-1,6 bonds) but not cellulose (β-1,4 bonds). Polysaccharides These are long chains of monosaccharide units and can be either branched or unbranched. Examples include: o Starch (energy storage in plants) o Glycogen (energy storage in animals) o Cellulose (structural component in plant cell walls) o Chitin (structural component in fungal cell walls and exoskeletons of arthropods) Carbohydrates play numerous essential roles in biological systems. Energy Source and Storage: Carbohydrates are a primary energy source for the body. Glucose, a simple sugar, is the main fuel used by cells for immediate energy. Complex carbohydrates like glycogen in animals and starch in plants store energy for later use. Structural Role: Carbohydrates contribute to structural integrity in both plants and animals. In plants, cellulose (a polysaccharide) is a major component of cell walls, providing rigidity and strength. In animals, carbohydrates are present in structures like the extracellular matrix and connective tissues. Cell Recognition and Signaling: Carbohydrates are present on the surfaces of cells, where they play a role in cell-cell recognition, communication, and immune response. Glycoproteins and glycolipids on cell membranes serve as markers that help cells recognize each other and signal to the immune system. Sparing Protein use for Energy: When adequate carbohydrates are available, the body is less likely to break down proteins for energy, allowing proteins to be used for other crucial functions, such as tissue repair and enzyme production. Preventing Ketosis: Carbohydrates prevent the body from entering ketosis, a state in which fats are broken down for energy, leading to the production of ketone bodies. While ketosis can be beneficial in some contexts, high levels can cause imbalance and potentially harmful effects. Fiber and Digestive Health: Dietary fiber, a non-digestible carbohydrate, promotes digestive health by aiding bowel movements, maintaining bowel health, and preventing conditions like constipation. Fiber also supports gut microbiota and can help regulate blood sugar levels and cholesterol. Configurations of Carbohydrates The configuration of carbohydrates is essential for their biological function, particularly in enzyme recognition and interaction with other biomolecules. 1. D- and L-Configuration Carbohydrates can exist as stereoisomers, and their configuration is based on the position of the hydroxyl group (-OH) on the penultimate carbon (the chiral carbon furthest from the carbonyl group). o D-configuration: The hydroxyl group is on the right. o L-configuration: The hydroxyl group is on the left. Most naturally occurring sugars are in the D-configuration. 2. Anomers In the cyclic form, the carbonyl carbon (C1 in aldoses, C2 in ketoses) becomes an anomeric carbon. Based on the position of the hydroxyl group attached to this carbon, the sugar can be either: o α-anomer: The hydroxyl group is below the plane of the ring. o β-anomer: The hydroxyl group is above the plane of the ring. 3. Epimers Epimers are sugars that differ in configuration at only one specific carbon atom. For example, glucose and galactose are epimers, differing at carbon 4. General Properties of Carbohydrates Carbohydrates are organic compounds composed of carbon (C), hydrogen (H), and oxygen (O), typically in a 1:2:1 ratio (Cₙ(H₂O)ₙ). They are one of the four main macromolecules essential for life and are known for their diverse biological functions, including energy storage, structural roles, and signaling. 1. Chemical Composition and Structure Basic Formula: The general formula for carbohydrates is (CH₂O)ₙ, where "n" is typically 3 or more. Monomers: Carbohydrates are made up of monosaccharide units, which are simple sugars like glucose, fructose, and galactose. They can link to form more complex carbohydrates (disaccharides, oligosaccharides, and polysaccharides). Functional Groups: Carbohydrates contain hydroxyl groups (-OH) and either an aldehyde group (-CHO) in aldoses (e.g., glucose) or a ketone group (C=O) in ketoses (e.g., fructose). 2. Isomerism Stereoisomerism: Carbohydrates exhibit stereoisomerism, where the spatial arrangement of atoms varies, but the molecular formula remains the same. For example, glucose has two stereoisomers: D-glucose and L-glucose. Enantiomers: Monosaccharides exist as enantiomers (mirror images), such as D- and L-forms, with D-sugars being the most biologically active in humans. Anomers: In cyclic forms, monosaccharides exhibit anomerism, which refers to the different positions of the hydroxyl group at the anomeric carbon (C1 in aldoses, C2 in ketoses). These can form α or β anomers (e.g., α-D-glucose and β-D-glucose). 3. Solubility Hydrophilic Nature: Carbohydrates are generally soluble in water due to the presence of numerous hydroxyl (-OH) groups, which form hydrogen bonds with water molecules. Solubility Variations: The solubility of carbohydrates decreases with increasing size. Monosaccharides and disaccharides (like glucose and sucrose) are highly soluble, while large polysaccharides (like cellulose or starch) are less soluble. 4. Taste Sweetness: Simple carbohydrates, especially monosaccharides (glucose, fructose) and disaccharides (sucrose), are sweet in taste. The degree of sweetness varies between sugars, with fructose being the sweetest. Polysaccharides: Larger carbohydrates like starch and cellulose do not have a sweet taste and are often tasteless due to their complex structure 5. Optical Activity Carbohydrates can rotate plane-polarized light, a property known as optical activity. This property is determined by the chiral centers (asymmetric carbons) in the molecule. Sugars are classified as dextrorotatory (D) if they rotate light to the right and levorotatory (L) if they rotate light to the left. 6. Reducing Properties Reducing Sugars: Monosaccharides and some disaccharides (like maltose and lactose) possess a free aldehyde or ketone group that allows them to act as reducing agents. They can reduce mild oxidizing agents like Benedict's solution or Fehling’s solution, leading to color changes, a property used in qualitative sugar tests. Non-Reducing Sugars: Disaccharides like sucrose lack a free aldehyde or ketone group due to the glycosidic bond between the two monosaccharides, making them non-reducing sugars. 7. Polymer Formation Glycosidic Bonds: Carbohydrates can form glycosidic bonds between monosaccharides through condensation reactions, where a water molecule is released. This leads to the formation of disaccharides, oligosaccharides, and polysaccharides (e.g., starch, cellulose, and glycogen). Branching: Some polysaccharides, like glycogen and amylopectin, have a branched structure due to α-1,6-glycosidic bonds in addition to α-1,4- glycosidic bonds. Sugars exhibit isomerism, which refers to the existence of molecules with the same molecular formula but different structural or spatial arrangements. In sugars, the main types of isomerism include: 1. Structural Isomerism: This occurs when molecules have the same molecular formula but different bonding arrangements. An example in sugars is glucose and fructose, which both have the formula C6H12​O6 but differ in their functional groups; glucose is an aldehyde (aldohexose), while fructose is a ketone (ketohexose). 2. Stereoisomerism: This occurs when molecules have the same molecular formula and sequence of bonded atoms but differ in the spatial arrangement. It includes: o Enantiomerism: This is a form of stereoisomerism where two molecules are non-superimposable mirror images of each other. For example, D-glucose and L-glucose are enantiomers. o Diastereomerism: Unlike enantiomers, diastereomers are stereoisomers that are not mirror images. D-glucose and D-mannose are diastereomers, differing in configuration around one carbon atom. 3. Anomeric Isomerism: This type of isomerism is specific to cyclic sugars. When sugars form rings, they create a new chiral center at the anomeric carbon (the carbon originally part of the carbonyl group). This results in two anomers: the alpha (α) and beta (β) forms, which differ in the position of the -OH group attached to the anomeric carbon. For example, α-D-glucose and β-D-glucose differ in the orientation of the hydroxyl group at the anomeric carbon. 4. Epimerism: Epimers are sugars that differ in configuration at just one of several chiral centers. For example, D- glucose and D-galactose are epimers, differing only in the configuration around the fourth carbon. A dextrorotatory substance is one that rotates the plane A levorotatory substance rotates the plane of of polarized light to the right, or clockwise, when viewed polarized light to the left, or counter clockwise, from the light source. when viewed from the light source.  Monosaccharides Monosaccharide carbohydrates are those carbohydrates that cannot be hydrolyzed further to give simpler units of polyhydroxy aldehyde or ketone. If a monosaccharide contains an aldehyde group then it is called aldose and on the other hand, if it contains a keto group then it is called a ketose. Monosaccharides Most monosaccharides have a sweet taste (fructose is sweetest; 73% sweeter than sucrose). They are solids at room temperature. They are extremely soluble in water: – Despite their high molecular weights, the presence of large numbers of OH groups make the monosaccharides much more water-soluble. Monosaccharides example Fischer projections and Haworth projections The sugars can be represented as Fischer projections and Haworth projections. Fisher projections show sugars in their open chain form. Haworth projections are often used to depict sugars in their cyclic forms. Fisher projection Haworth projection Functions of Monosaccharides Glucose (C6H12O6) is an important source of energy in humans and plants. Plants synthesize glucose using carbon dioxide and water, which in turn is used for their energy requirements. The presence of galactose is in milk sugar (lactose), and fructose in fruits and honey makes these foods sweet. Ribose is a structural element of nucleic acids and some coenzymes. Mannose is a constituent of mucoproteins and glycoproteins required for the proper functioning of the body.  Disaccharides Disaccharide, also called double sugar, any substance that is composed of two molecules of simple sugars (monosaccharide) linked to each other by a glycosidic bond. Disaccharides are crystalline water-soluble compounds. The monosaccharides within them are linked by a glycosidic bond (or glycosidic linkage), the position of which may be designated α- or β- or a combination of the two (α-,β-). The three major disaccharides are sucrose, lactose, and maltose. A disaccharide results when two monosaccharides are joined in a chemical process called dehydration synthesis, which causes two monosaccharides to combine, losing a water molecule in the process.  Disaccharides (C12H22O11) are sugars composed of two monosaccharide units that are joined by a carbon–oxygen-carbon linkage known as a glycosidic linkage. This linkage is formed from the reaction of the anomeric carbon of one cyclic monosaccharide with the OH group of a second monosaccharide. Note An anomeric carbon is the carbon atom in a cyclic sugar that bears the aldehyde or ketone functional group. It's the carbon atom that forms the alpha or beta anomer. Sucrose Sucrose, which is formed following photosynthesis in green plants, consists of one molecule of glucose and one of fructose bonded via an α-,β-linkage. Lactose Lactose (milk sugar), found in the milk of all mammals, consists of glucose and galactose connected by a β linkage. Maltose Maltose, a product of the breakdown of starches during digestion, consists of two molecules of glucose connected via an α-linkage. Functions of Disaccharides Sucrose is a product of photosynthesis, which functions as a major source of carbon and energy in plants. Lactose is a primary sugar found in milk and is major source of energy in mammals. Maltose is an important intermediate in starch and glycogen digestion. Trehalose is an essential energy source for insects. Cellobiose is essential in carbohydrate metabolism. Gentiobiose is a constituent of plant glycosides.  Oligosaccharides Oligosaccharides are compounds that yield 3 to 10 molecules of the same or different monosaccharides on hydrolysis. Based on the number of monosaccharides attached, the oligosaccharides are classified as trisaccharides, tetrasaccharides, pentasaccharides, and so on. The oligosaccharides are normally present as glycans. They are linked to either lipids or amino acid side chains in proteins by N- or O-glycosidic bonds known as glycolipids or glycoproteins.  Polysaccharides contain more than 10 Polysaccharides monosaccharide units and can be hundreds of sugar units in length. They are also called as “glycans”. Polysaccharides are classified based on Their functions The type of monosaccharide units they contain. Based on the type of monosaccharides involved in the formation of polysaccharide structures, they are classified into two groups: homopolysaccharides and heteropolysaccharides. Based on functions they are called as. structural proteins and storage proteins. Homopolysaccharides They are composed of repeating units of only one type of monomer. A few examples of homopolysaccharides include cellulose, starches (amylose and amylopectin), glycogen, chitin and xylans. 1. Cellulose is a linear, unbranched polymer of glucose units joined by beta 1-4 linkages. It’s one of the most abundant organic compounds in the biosphere. 2. Starch is made of repeating units of D-glucose that are joined together by alpha-linkages. It’s one of the most abundant polysaccharides found in plants and is composed of a mixture of amylose (15-20%) and amylopectin (80-85%) Heteropolysaccharides They are composed of two or more repeating units of different types of monomers. Examples include glycosaminoglycans, peptidoglycans, and agarose. In natural systems, they are linked to proteins, lipids, and peptides. Glycosaminoglycans (GAG) are negatively charged unbranched heteropolysaccharides. They are composed of repeating units of disaccharides Amino acids like N-acetylglucosamine or N- acetylgalactosamine and uronic acid (like glucuronic acid) are normally present in the GAG structure. E.g. Hyaluronic acid Hyaluronic acid is made up of D-Glucuronic acid and N-acetylglucosamine Polysaccharides, long chains of monosaccharide units linked by glycosidic bonds, play diverse and essential roles in biological systems. Their functions can generally be grouped into structural, storage, protective, and functional roles: 1. Energy Storage: o Starch (in plants) and glycogen (in animals) serve as primary energy storage polysaccharides. o Starch, composed of amylose and amylopectin, stores energy for plants and is a major energy source for animals and humans when consumed. o Glycogen, stored in the liver and muscles, provides a quick energy source for animals, especially during intense physical activity. 2. Structural Support: o Cellulose in plants is a structural polysaccharide that provides rigidity to plant cell walls, allowing them to maintain shape and resist external stress. This structural role is crucial for plant stability and growth. o Chitin, found in the exoskeletons of insects, crustaceans, and fungi, provides both strength and flexibility. It is the second most abundant polysaccharide in nature after cellulose. 3. Protection: o Mucopolysaccharides (or glycosaminoglycans) like hyaluronic acid, heparin, and chondroitin sulfate are found in connective tissues, cartilage, and the extracellular matrix in animals. They provide cushioning, lubrication, and structural support in joints, skin, and other tissues. o Bacterial polysaccharides, such as the capsule around certain bacterial cells, help protect against environmental stress, dehydration, and immune attacks. 4.Cell Communication and Adhesion: o Glycoproteins and glycolipids on cell surfaces contain polysaccharide chains that contribute to cell signaling and recognition. These help cells communicate, adhere to each other, and form tissues, and they play roles in immune response, infection prevention, and tissue repair. o Polysaccharides like pectin in plants also aid in cellular adhesion by helping bind plant cells together within tissues. 5.Water Retention and Gel Formation: o Certain polysaccharides, like agar, alginate, and carrageenan, have gel-forming properties and are used to retain water and create gel-like textures in foods, cosmetics, and pharmaceuticals. o In plants, polysaccharides such as pectins help retain water in cell walls, maintaining turgor pressure and providing flexibility. 6.Defense Mechanism: o Some plants produce polysaccharides as part of their immune response to protect against pathogens. For example, callose is deposited at infection sites in plants, creating a physical barrier against pathogens. o Polysaccharides in the cell walls of fungi and bacteria, such as peptidoglycan in bacterial cell walls, provide structural protection and shield the cells from environmental threats.