Module 3 Molecules of Life: Structure and Function of Biological Macromolecules

Molecules of Life

Key Terms and Definitions

• Organic compound: A chemical compound containing carbon atoms bonded to hydrogen, often with other elements such as oxygen, nitrogen, sulfur, or phosphorus.

• Functional group: A specific group of atoms within a molecule responsible for characteristic chemical reactions.

• Hydroxyl group (-OH): A polar functional group found in alcohols; increases solubility in water.

• Phosphate group (-PO4): A functional group important in energy transfer (e.g., ATP).

• Methyl group (-CH3): A nonpolar group that can affect gene expression and molecular shape.

• Carboxyl group (-COOH): A functional group found in organic acids; acts as an acid by donating H+.

• Amino group (-NH2): A functional group that acts as a base; found in amino acids.

• Sulfhydryl (thiol) group (-SH): Important for stabilizing protein structure via disulfide bonds.

• Monomer: A small molecule that can join with others to form a polymer.

• Polymer: A large molecule made of repeating monomer units.

• Dehydration synthesis (condensation): A reaction that joins two molecules by removing a water molecule.

• Hydrolysis: A reaction that breaks a bond in a molecule by adding water.

• Carbohydrate: Organic molecules composed of carbon, hydrogen, and oxygen; main energy source for cells.

• Monosaccharide: Simple sugar; monomer of carbohydrates (e.g., glucose).

• Disaccharide: Two monosaccharides joined by a glycosidic bond (e.g., sucrose).

• Polysaccharide: Large carbohydrate made of many monosaccharides (e.g., starch, cellulose).

• Glycogen: Animal storage form of glucose; highly branched polysaccharide.

• Starch: Plant storage form of glucose; less branched than glycogen.

• Cellulose: Structural polysaccharide in plant cell walls; unbranched and forms fibers.

• Lipid: Hydrophobic organic molecule, including fats, oils, and sterols.

• Fatty acid: Long hydrocarbon chain with a carboxyl group; building block of lipids.

• Fat: Triglyceride; energy storage molecule in animals.

• Oil: Liquid fat at room temperature; usually from plants.

• Sterol (Steroid): Lipid with four fused rings; includes cholesterol and hormones.

• Triglyceride: Lipid made of three fatty acids and one glycerol.

• Saturated fat: Fatty acid chains with no double bonds; solid at room temperature.

• Unsaturated fat: Fatty acid chains with one or more double bonds; liquid at room temperature.

• Amino acid: Monomer of proteins; contains amino, carboxyl, and R group.

• Peptide bond: Covalent bond joining amino acids in a protein.

• R group: Side chain of an amino acid; determines its properties.

• Polypeptide: Chain of amino acids linked by peptide bonds.

• Protein: Functional biological molecule made of one or more polypeptides.

• Primary structure: Linear sequence of amino acids in a protein.

• Secondary structure: Local folding (e.g., alpha helix, beta sheet) stabilized by hydrogen bonds.

• Tertiary structure: Overall 3D shape of a polypeptide; stabilized by various bonds and interactions.

• Quaternary structure: Association of multiple polypeptide chains in a protein.

• Denaturation: Loss of protein structure (and function) due to environmental changes.

• Nucleotide: Monomer of nucleic acids; consists of a sugar, phosphate, and nitrogenous base.

• Nitrogenous base: Component of nucleotides; includes adenine, thymine, cytosine, guanine, uracil.

• DNA (Deoxyribonucleic acid): Double-stranded nucleic acid; stores genetic information.

• RNA (Ribonucleic acid): Single-stranded nucleic acid; involved in protein synthesis.

• Deoxyribose: Five-carbon sugar in DNA.

• Ribose: Five-carbon sugar in RNA.

• Double helix: Structure of DNA; two strands coiled around each other.

• Antiparallel: Orientation of DNA strands running in opposite directions.

• Sugar-phosphate backbone: Repeating pattern of sugar and phosphate in nucleic acids.

• Complementary base pairing: Specific pairing of bases (A-T/U, G-C) in DNA/RNA.

Importance of Carbon in Organic Compounds

Carbon is central to organic chemistry because it can form four covalent bonds, allowing for a diversity of stable, complex molecules. Its ability to bond with itself and other elements leads to a variety of molecular structures, including chains, rings, and branches.

Functional Groups in Organic Molecules

• Functional groups determine the chemical reactivity and properties of organic molecules.

• Common functional groups include hydroxyl, carboxyl, amino, phosphate, methyl, and sulfhydryl.

• For example, the carboxyl group acts as an acid, while the amino group acts as a base.

Monomers and Polymers

• Monomers are the building blocks of polymers.

• Examples: Glucose (monomer of starch), amino acids (monomers of proteins), nucleotides (monomers of nucleic acids).

• Polymers are large molecules made by linking monomers through covalent bonds.

Condensation (Dehydration Synthesis) and Hydrolysis

• Dehydration synthesis: Joins two monomers by removing a water molecule.

• Hydrolysis: Breaks a polymer into monomers by adding water.

Equation for Dehydration Synthesis:

$\mathrm{Monomer}_1 + \mathrm{Monomer}_2 \xrightarrow{\text{dehydration}} \mathrm{Polymer} + \mathrm{H}_2\mathrm{O}$

Equation for Hydrolysis:

$\mathrm{Polymer} + \mathrm{H}_2\mathrm{O} \xrightarrow{\text{hydrolysis}} \mathrm{Monomer}_1 + \mathrm{Monomer}_2$

Carbohydrates: Structure and Function

• General formula: $(\mathrm{CH}_2\mathrm{O})_n$

• Major uses: Energy source (glucose), energy storage (starch, glycogen), structural support (cellulose).

Types of Carbohydrates

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides joined (e.g., sucrose = glucose + fructose).

• Polysaccharides: Many monosaccharides linked (e.g., starch, glycogen, cellulose).

Properties of Glycogen, Starch, and Cellulose

• Glycogen: Highly branched; energy storage in animals.

• Starch: Moderately branched; energy storage in plants.

• Cellulose: Unbranched; structural component in plant cell walls; not digestible by humans.

Lipids: Structure and Function

• Composed mainly of hydrocarbons; hydrophobic due to nonpolar C-H bonds.

• Major types: Fats, oils, phospholipids, sterols.

• Functions: Energy storage, membrane structure, signaling molecules.

Saturated vs. Unsaturated Fats

• Saturated fats: No double bonds; straight chains; solid at room temperature (e.g., butter).

• Unsaturated fats: One or more double bonds; kinked chains; liquid at room temperature (e.g., olive oil).

• Double bonds in unsaturated fats prevent tight packing, lowering melting point.

Amino Acids and Proteins

• General structure: Central carbon, amino group, carboxyl group, hydrogen, and R group (side chain).

• R group chemistry determines the properties (e.g., polar, nonpolar, acidic, basic) of each amino acid.

• Peptide bond: Covalent bond between amino group of one amino acid and carboxyl group of another.

Levels of Protein Structure

• Primary: Sequence of amino acids.

• Secondary: Local folding (alpha helix, beta sheet) via hydrogen bonds.

• Tertiary: 3D shape stabilized by interactions (hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic interactions).

• Quaternary: Association of multiple polypeptide chains.

Protein Denaturation

• Loss of structure and function due to heat, pH changes, or chemicals.

• Example: Cooking an egg denatures egg white proteins.

Nucleic Acids: DNA and RNA

• Nucleotide structure: Phosphate group, five-carbon sugar (deoxyribose or ribose), nitrogenous base.

• DNA nucleotides: Deoxyribose sugar; bases A, T, G, C.

• RNA nucleotides: Ribose sugar; bases A, U, G, C.

Structure of DNA

• Double helix with antiparallel strands.

• Sugar-phosphate backbone on the outside; bases paired inside (A-T, G-C) via hydrogen bonds.

Functions of Nucleic Acids and Nucleotides

• DNA: Stores genetic information.

• RNA: Involved in protein synthesis and gene regulation.

• Nucleotides: Also function as energy carriers (e.g., ATP) and signaling molecules.

Table: Comparison of DNA and RNA

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Strands	Double-stranded	Single-stranded
Nitrogenous Bases	A, T, G, C	A, U, G, C
Function	Genetic information storage	Protein synthesis, gene regulation

Example: ATP (adenosine triphosphate) is a nucleotide that stores and transfers energy in cells.

Additional info: This guide expands on the objectives by providing definitions, explanations, and examples for each key concept, ensuring a comprehensive overview suitable for exam preparation.