Molecules of Life

Major Classes of Biological Molecules

All living organisms are composed of four main classes of organic molecules: carbohydrates, lipids, proteins, and nucleic acids. These molecules serve as the building blocks of life, each with unique structures and functions essential for cellular processes.

• Carbohydrates: Organic compounds made of carbon, hydrogen, and oxygen, typically with a 1:2:1 ratio. They provide energy and structural support. Examples: Glucose, Galactose, Fructose (monosaccharides).

• Lipids: Hydrophobic molecules including fats, oils, and phospholipids. They store energy, insulate, and form cell membranes. Examples: Glycerol, Fatty acids, Triglycerides.

• Proteins: Polymers of amino acids, containing an amino group, carboxylic acid group, and a variable R side chain. They perform structural, enzymatic, and regulatory functions. Examples: Alanine, Cysteine (amino acids).

• Nucleic Acids: Polymers of nucleotides, which include a sugar, phosphate group, and nitrogenous base. They store and transmit genetic information. Examples: DNA, RNA (nucleotides shown in model).

Key Structural Features

• Carbohydrates have ring structures with multiple hydroxyl (–OH) groups.

• Lipids have long hydrocarbon chains (fatty acids) and a glycerol backbone. Triglycerides are formed from glycerol and three fatty acids.

• Proteins have a central (alpha) carbon bonded to an amino group (–NH2), carboxyl group (–COOH), hydrogen, and a variable R group.

• Nucleic acids have a sugar-phosphate backbone and nitrogenous bases (A, T, C, G, U).

Table: Comparison of Major Biological Molecules

Biochemical Reactions

Types of Biochemical Reactions

Cells build and break down molecules through specific chemical reactions. The two main types are dehydration synthesis (condensation) and hydrolysis.

• Dehydration Synthesis: Joins two molecules by removing a water molecule. Forms bonds such as glycosidic (carbohydrates), peptide (proteins), and ester (lipids).

• Hydrolysis: Breaks a bond by adding water, splitting large molecules into smaller units.

Examples of Biochemical Reactions

• Carbohydrate Synthesis: Glucose + Fructose → Sucrose + H2O

• Protein Synthesis: Amino acid 1 + Amino acid 2 → Dipeptide + H2O

• Lipid Synthesis: Glycerol + Fatty acid → Monoglyceride + H2O

Bond Types Formed

• Glycosidic bond: Joins monosaccharides in carbohydrates.

• Peptide bond: Joins amino acids in proteins.

• Ester bond: Joins fatty acids to glycerol in lipids.

Enzymatic Hydrolysis

• Hydrolysis reactions use water to break bonds, releasing monomers from polymers.

• Enzymes that catalyze hydrolysis often have names ending in -ase (e.g., lipase, protease).

Properties and Functions of Biological Molecules

Carbohydrates

• Primary source of quick energy for cells.

• Stored as glycogen in animals and starch in plants.

• Contain sugar, often with a ring structure.

Lipids

• Store energy more efficiently than carbohydrates.

• Form cell membranes (phospholipids).

• Insulate and protect organs.

• Saturated fatty acids: No double bonds, straight chains, solid at room temperature.

• Unsaturated fatty acids: One or more double bonds, kinked chains, liquid at room temperature.

Table: Saturated vs. Unsaturated Fatty Acids

Proteins

• Made of 20 different amino acids, each with a unique R group.

• Functions include catalysis (enzymes), structure (collagen), transport (hemoglobin), and signaling (hormones).

• All amino acids share an amino group, carboxyl group, and central carbon.

Nucleic Acids

• DNA and RNA store and transmit genetic information.

• Composed of nucleotides (sugar, phosphate, nitrogenous base).

Scientific Concepts and Applications

Energy in Biological Molecules

• Breaking bonds requires energy; forming bonds releases energy.

• Cells use carbohydrates for quick energy because they are easily broken down.

• Lipids provide long-term energy storage.

Role of Water in Metabolism

• Water is essential for hydrolysis reactions, breaking down polymers into monomers.

• Water acts as a solvent, medium for chemical reactions, and helps regulate temperature.

Trans Fats

• Trans fats are artificially created by hydrogenating unsaturated fats, making them solid at room temperature.

• Associated with negative health effects.

Key Equations

• General formula for monosaccharides:

• Dehydration synthesis (example):

• Hydrolysis (example):

Example

• Formation of a peptide bond: Two amino acids join via dehydration synthesis, releasing water and forming a dipeptide.

• Hydrolysis of sucrose: Sucrose + H2O → Glucose + Fructose

Additional info: Some explanations and context have been expanded for clarity and completeness, including the comparison tables and definitions of key terms.