TLDR;
This video by Physics Wallah discusses carbohydrates, covering their classification based on sugar units and reducing properties, the structure of monosaccharides, and examples of polysaccharides. It explains the general formula of carbohydrates, different types of sugars (monosaccharides, disaccharides, oligosaccharides, and polysaccharides), and their properties. The video also touches on the structure and examples of monosaccharides, including glucose, galactose, and fructose, and explains the formation of glycosidic bonds in disaccharides and polysaccharides.
- Carbohydrates are classified based on the number of sugar units and their reducing properties.
- Monosaccharides are simple sugars with a general formula of (CH2O)n.
- Polysaccharides are complex carbohydrates made up of many monosaccharide units.
Introduction [0:00]
The video starts with a greeting and an introduction to the topic of carbohydrates. The instructor mentions that previous classes covered amino acids, proteins, and nucleic acids, and this lecture will focus on carbohydrates, also known as sugars.
Carbohydrate Basics and Classification [1:20]
The term "carbohydrate" means "hydrate of carbon," with a general formula of (CH2O)n, applicable mainly to monosaccharides. Carbohydrates are not always sweet. They are classified based on the number of sugar units: monosaccharides (single sugar unit), disaccharides (two sugar units), oligosaccharides (2-10 sugar units), and polysaccharides (more than 10 sugar units). Sugars are also classified as reducing or non-reducing. Monosaccharides are reducing sugars, while polysaccharides are non-reducing. Disaccharides can be either reducing (like lactose and maltose) or non-reducing (like sucrose).
Monosaccharides: Structure and Examples [6:15]
Monosaccharides contain 3 to 7 carbon atoms. Their general formula is (CH2O)n. Examples include trioses (3 carbons), tetroses (4 carbons), pentoses (5 carbons), hexoses (6 carbons), and heptoses (7 carbons). Depending on the carbonyl group's position, they are classified as aldoses (aldehyde group) or ketoses (ketone group). Examples of aldoses include glyceraldehyde, ribose, glucose, and galactose. Examples of ketoses include dihydroxyacetone, ribulose, and fructose.
Disaccharides: Formation and Examples [10:14]
Disaccharides are formed from two monosaccharide units. Lactose is formed from galactose and glucose, maltose from two glucose units, and sucrose from glucose and fructose. It's important to remember the constituent monosaccharides of common disaccharides. Lactose is found in milk, maltose in malt, and sucrose in sugarcane. Glycosidic bonds link the monosaccharide units, formed by removing a water molecule.
Oligosaccharides [13:39]
Oligosaccharides contain 3 to 10 sugar units. If there are two sugar units, they are called disaccharides; three units, trisaccharides; and four units, tetrasaccharides.
Polysaccharides: Types and Examples [14:39]
Polysaccharides contain more than 10 monosaccharide units. They are classified as homopolysaccharides (same sugar units) or heteropolysaccharides (different sugar units). Examples of homopolysaccharides include starch, glycogen, cellulose, inulin, and chitin. Examples of heteropolysaccharides include hyaluronic acid and keratin sulfate.
Homopolysaccharides: Starch, Glycogen, Cellulose, Inulin and Chitin [16:59]
Starch is a homopolysaccharide made of glucose units and is the storage form of glucose in plants. It consists of amylose (linear chains) and amylopectin (branched chains). Glycogen is the storage form of glucose in animals and is highly branched. Cellulose is a structural component of plant cell walls, made of beta-glucose units linked by beta 1-4 glycosidic bonds. Inulin is made of fructose units and is found in tubers and roots. Chitin is a structural component of fungal cell walls and arthropod exoskeletons, made of N-acetylglucosamine units.
Heteropolysaccharides: Hyaluronic Acid and Keratan Sulfate [17:46]
Hyaluronic acid is a heteropolysaccharide found in connective tissues and has water-retaining properties, used in beauty treatments. Keratan sulfate is found in cartilage.
Monomeric Units of Polysaccharides [21:25]
Starch, glycogen, and cellulose are made of glucose units, while inulin is made of fructose units, and chitin is made of N-acetylglucosamine.
Structure of Monosaccharides: Linear and Ring Forms [23:41]
Monosaccharides exist in linear and ring forms. Ring structures can be either pyranose (six-membered ring) or furanose (five-membered ring). Pyranose rings have five carbon atoms and one oxygen atom, while furanose rings have four carbon atoms and one oxygen atom. Glucose forms a pyranose ring, while fructose forms a furanose ring.
Isomerism in Monosaccharides: Epimers and Anomers [29:37]
Epimers are isomers that differ in the configuration around a single carbon atom. For example, glucose and galactose are epimers at carbon 4, and glucose and mannose are epimers at carbon 2. Anomers are isomers that differ in the configuration at the anomeric carbon (carbon 1 in aldoses and carbon 2 in ketoses). Alpha and beta forms of glucose are anomers.
Glycosidic Bond Formation [41:30]
Glycosidic bonds are formed between two monosaccharides by removing a water molecule. The bond is formed between the hydroxyl groups of the two sugars. For example, in maltose, the glycosidic bond is formed between carbon 1 of one glucose molecule and carbon 4 of another glucose molecule (1-4 linkage).
Disaccharides: Maltose, Lactose, and Sucrose [45:57]
Maltose consists of two glucose units linked by an alpha 1-4 glycosidic bond. Lactose consists of galactose and glucose linked by a beta 1-4 glycosidic bond. Sucrose consists of glucose and fructose linked by an alpha 1-2 glycosidic bond.
Polysaccharides: Starch and Glycogen Structure [51:16]
Starch is a homopolysaccharide made of glucose units and is the storage form of glucose in plants. It consists of amylose (linear chains with alpha 1-4 linkages) and amylopectin (branched chains with alpha 1-4 linkages and alpha 1-6 linkages at branch points). Glycogen is the storage form of glucose in animals and is highly branched with alpha 1-4 linkages and alpha 1-6 linkages at branch points.
Polysaccharides: Inulin and Cellulose [57:23]
Inulin is made of fructose units linked by beta 1-4 glycosidic bonds and is found in tubers and roots. Cellulose is a structural component of plant cell walls, made of beta-glucose units linked by beta 1-4 glycosidic bonds.
Muco-polysaccharides [1:00:22]
Muco-polysaccharides are polysaccharides that can retain water. Examples include mucilage found in ladyfingers (okra) and aloe vera. Isabgol, used for constipation relief, contains mucilage.