Study Guide: Biological Molecules (General Biology)

Biological Molecules

Introduction

Biological molecules, also known as biomolecules, are essential compounds that make up living organisms. They include a variety of organic molecules with diverse structures and functions, enabling the complexity of life. This chapter focuses on the structure, formation, and function of the four major classes of biomolecules: carbohydrates, lipids, proteins, and nucleic acids.

Organic Molecules

Definition and Characteristics

• Organic molecules are compounds primarily composed of carbon atoms bonded with hydrogen, oxygen, nitrogen, and other elements.

• Carbon can form four covalent bonds, allowing for a wide variety of molecular shapes and sizes, including chains, rings, and branched structures.

• This versatility enables the formation of complex molecules necessary for life.

• Significance: The diversity of carbon-based molecules underlies the complexity and adaptability of biological systems.

Functional Groups

Role in Biomolecules

• Functional groups are specific groups of atoms within molecules that determine the chemical properties and reactions of those molecules.

• Common functional groups in biology include amino (-NH2), carboxyl (-COOH), hydroxyl (-OH), and phosphate (-PO4).

• For example, amino acids contain both amino and carboxyl groups; ATP contains phosphate groups.

Polymers and Monomers

Formation and Breakdown

• Polymers are large molecules made by joining many smaller units called monomers.

• Dehydration synthesis (condensation reaction): Monomers are joined by covalent bonds through the removal of a water molecule.

• Hydrolysis: Polymers are broken down into monomers by the addition of water, breaking covalent bonds.

Example: The formation of a disaccharide from two monosaccharides by dehydration synthesis, releasing water.

Major Groups of Biomolecules

Overview and Characteristics

• The four major groups are carbohydrates, lipids, proteins, and nucleic acids.

• Each group has unique monomers, functions, and interactions with water (hydrophobic or hydrophilic).

BioMolecule Group	Uses in Organisms	Monomers or Common Subunits	Reaction to Water
Carbohydrates	Energy storage, structural support	Monosaccharides (e.g., glucose)	Hydrophilic
Lipids	Energy storage, membrane structure, signaling	Glycerol and fatty acids	Hydrophobic
Proteins	Catalysis, structure, transport, signaling	Amino acids	Varies (depends on R group)
Nucleic Acids	Information storage and transfer	Nucleotides	Hydrophilic

Carbohydrates

Monosaccharides and Polysaccharides

• Monosaccharides are simple sugars with a general formula of (CH2O)n (e.g., glucose: C6H12O6).

• Glucose is the most biologically important monosaccharide.

• Disaccharides form when two monosaccharides join via dehydration synthesis (e.g., glucose + fructose → sucrose + H2O).

• Polysaccharides are long chains of monosaccharides. Four highlighted in biology are:

  • Starch (energy storage in plants)

  • Glycogen (energy storage in animals)

  • Cellulose (structural support in plant cell walls)

  • Chitin (structural support in fungi and arthropods)

• All are polymers of glucose but differ in the type of glycosidic bonds and branching, leading to different properties.

Lipids

Characteristics and Types

• Lipids are a diverse group of hydrophobic molecules, grouped together by their insolubility in water.

• Major types include triacylglycerols (fats and oils) and phospholipids (major component of cell membranes).

• Triacylglycerol consists of three fatty acids linked to a glycerol molecule.

• Phospholipids have two fatty acids and a phosphate group attached to glycerol, giving them both hydrophobic and hydrophilic regions.

• Saturated fats have no double bonds between carbon atoms; unsaturated fats have one or more double bonds.

• Saturated fats are typically solid at room temperature (common in animals), while unsaturated fats are liquid (common in plants).

Proteins

Structure and Function

• Proteins perform a wide range of functions: catalysis (enzymes), structure (collagen), transport (hemoglobin), signaling (hormones), and more.

• The diversity of protein function is due to the variety of amino acids (20 different types), each with a unique R group.

• Monomer: Amino acid. Peptide bonds link amino acids together.

• Each amino acid has a central carbon, an amino group, a carboxyl group, a hydrogen atom, and an R group (side chain).

• Dehydration synthesis joins amino acids, forming peptide bonds and releasing water.

• The properties of the R group determine the behavior of the amino acid in proteins (e.g., hydrophobic, hydrophilic, acidic, basic).

Levels of Protein Structure

• Primary structure: Sequence of amino acids.

• Secondary structure: Local folding (α-helix, β-sheet) stabilized by hydrogen bonds.

• Tertiary structure: Overall 3D shape, stabilized by interactions among R groups (hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic interactions).

• Quaternary structure: Association of multiple polypeptide chains.

• Denaturation disrupts secondary, tertiary, and quaternary structures, often rendering the protein nonfunctional. Causes include heat, pH changes, and chemicals. Denaturation is sometimes reversible, but often is not.

Nucleic Acids

Basic Information

• Nucleic acids (DNA and RNA) store and transmit genetic information.

• Monomer: Nucleotide (composed of a sugar, phosphate group, and nitrogenous base).

• Further details on nucleic acids will be covered in later chapters.