Biology Chapter on Macromolecules

The Molecules of Life

• All living organisms are composed of four main types of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids.
• Macromolecules are large molecules constructed from thousands of covalently linked atoms.
• Molecular structure and function are interconnected.

Macromolecules are polymers, built from monomers

• Polymers are long molecules comprised of repeating smaller subunits called monomers.
• Carbohydrates, proteins, and nucleic acids are all polymers.

Synthesis and Breakdown of Polymers

• Dehydration reactions create bonds between monomers by removing a water molecule.
• Hydrolysis breaks down polymers by adding a water molecule, breaking the bonds.

Carbohydrates serve as fuel and building material

• Carbohydrates include sugars and polymers of sugars.
• Monosaccharides are simple sugars, while polysaccharides are polymers of many sugar units.

Sugars

• Monosaccharides have molecular formulas that are multiples of CH2O.
• The most common monosaccharide is glucose (C6H12O6).
• Monosaccharides are classified as either aldoses (containing an aldehyde group) or ketoses (containing a ketone group), and by the number of carbon atoms.

Polysaccharides

• Polysaccharides serve as storage or structural molecules.
• Their structure and function are determined by the arrangement of their sugar monomers and glycosidic linkages.

Storage Polysaccharides

• Starch is a storage polysaccharide in plants, composed of glucose monomers.
• Plants store starch as granules within chloroplasts and other plastids.
• Amylose is the simplest form of starch.
• Glycogen is a storage polysaccharide in animals, primarily stored in liver and muscle cells.

Structural Polysaccharides

• Cellulose is a major component of plant cell walls, also composed of glucose monomers.
• Cellulose and starch differ in the configuration of their glycosidic linkages, which affects their structure.
• Cellulose has a straight, fibrous structure due to its  glucose monomers.
• These fibers create strong building materials for plants.
• Humans lack the enzymes to break down cellulose, which is why it’s considered dietary fiber.
• Chitin is a structural polysaccharide found in the exoskeletons of arthropods, and the cell walls of fungi.

Lipids are a diverse group of hydrophobic molecules

• Lipids are a class of non-polymer large biological molecules.
• They are hydrophobic because they consist mostly of hydrocarbons.
• The main types of lipids are fats, phospholipids, and steroids.

Fats

• Fats are constructed from glycerol and fatty acids.
• Glycerol is a three-carbon alcohol with a hydroxyl group on each carbon.
• Fatty acids have a carboxyl group attached to a long carbon chain.
• Three fatty acids join to glycerol via ester linkages to form a triacylglycerol, or triglyceride.

Fatty Acids

• Fatty acids vary in length and the number and position of their double bonds.
• Saturated fatty acids have no double bonds and are solid at room temperature.
• Unsaturated fatty acids contain one or more double bonds and are liquid at room temperature.
• Essential fatty acids, like omega-3 fatty acids, are not synthesized in the body and must be consumed.

Functions of Fats

• Fats serve primarily for energy storage.
• Mammals store fat in adipose cells, which also cushions vital organs and provides insulation.

Phospholipids

• Phospholipids contain two fatty acids and a phosphate group attached to glycerol.
• The fatty acid tails are hydrophobic, while the phosphate group and its attachments form a hydrophilic head.
• In water, phospholipids form a bilayer with hydrophobic tails facing inward and hydrophilic heads facing outward.
• They are the major component of all cell membranes.

Steroids

• Steroids have a distinct structure with four fused rings.
• Cholesterol is an important steroid found in animal cell membranes.
• High cholesterol levels in the blood can contribute to cardiovascular disease.

Proteins include a diversity of structures with a wide range of functions

• Proteins make up over 50% of the dry mass of most cells.
• They perform various functions including structural support, storage, transport, cellular communication, movement, and defense.

Protein Functions

• Enzymatic proteins catalyze chemical reactions.
• Defensive proteins protect against disease.
• Storage proteins store amino acids.
• Transport proteins transport substances.
• Hormonal proteins coordinate cellular activities.
• Receptor proteins bind to signaling molecules.
• Contractile and motor proteins facilitate movement
• Structural proteins provide support.