Polysaccharides Overview

Polysaccharides

• Polysaccharides are long chains of monosaccharides linked by glycosidic bonds, categorized as "poly-" meaning "many."
• Their molecular weight can exceed 100,000 daltons, depending on the number of monomers.
• Primary examples include starch, glycogen, cellulose, and chitin.
• Starch is the energy storage form in plants, consisting of amylose (unbranched glucose chains) and amylopectin (branched glucose chains).
• Excess glucose in plants is stored as starch in roots and seeds, providing food for germinating embryos and serving as a food source for humans and animals.
• Enzymes like salivary amylases break down starch into smaller molecules (maltose and glucose) for cellular absorption.
• Starch links glucose monomers via α 1-4 and α 1-6 glycosidic bonds.
• Glycogen, analogous to starch, is the glucose storage form in humans, highly branched, and stored mainly in liver and muscle cells.
• Glycogenolysis is the process where glycogen is broken down to release glucose when blood sugar levels are low.
• Cellulose is the most abundant natural biopolymer, primarily found in plant cell walls for structural support.
• Cellulose consists of glucose monomers linked by β 1-4 glycosidic bonds, resulting in a linear, fibrous structure.

Lipids

• Lipids are a diverse group of largely nonpolar compounds, primarily consisting of hydrocarbons that are hydrophobic (insoluble in water).
• Functions include energy storage, insulation, and serving as building blocks for hormones and cellular membranes.
• Types of lipids encompass fats, oils, waxes, phospholipids, and steroids.
• Fats consist of glycerol and fatty acids, with glycerol having three carbons and hydroxyl groups.
• Fatty acids range from 4 to 36 carbons, with common lengths being 12–18 carbons.
• Formation of fat involves ester bond creation between fatty acids and glycerol, resulting in triacylglycerols (triglycerides) and releasing three water molecules.
• Fatty acids can be saturated (only single bonds) or unsaturated (one or more double bonds).
• Saturated fats are solid at room temperature, while unsaturated fats are generally liquid, categorized as mono- or polyunsaturated based on double bond quantity.
• Unsaturated fats, including oils, help lower blood cholesterol, whereas saturated fats may contribute to plaque in arteries.
• Trans fats arise from the hydrogenation of oils, posing health risks by increasing "bad" LDL cholesterol levels.

Proteins

• Proteins are abundant organic molecules with diverse functions: structural, regulatory, transport, storage, and enzymatic roles.
• Composed of polymers of amino acids, the unique sequence determines the structure and function.
• Twenty types of amino acids are the building blocks, each featuring a central carbon, amino group, carboxyl group, hydrogen atom, and a distinct R group.
• Ten amino acids are essential for humans, obtained solely through diet.
• Peptide bonds form between amino acids via dehydration synthesis, linking the carboxyl group of one to the amino group of another, resulting in a water molecule release.