Chapter 5 STUDY GUIDE - General Biology: Macromolecules and Their Biological Roles

Macromolecules: Structure and Function

Introduction to Macromolecules

Macromolecules are large, complex molecules essential for life, including carbohydrates, lipids, proteins, and nucleic acids. Their structure determines their function in biological systems.

• Monomers and Polymers: Monomers are small, repeating units that join to form polymers through chemical reactions.

• Dehydration Synthesis: The process by which monomers are joined, releasing water. $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + \text{H}_2\text{O}$

• Hydrolysis: The process by which polymers are broken down into monomers by adding water.

• Enzymes: Biological catalysts that speed up chemical reactions, including those involved in building and breaking down macromolecules.

• Metabolism of Macromolecules: The breakdown and synthesis of macromolecules are central to many diseases and biological processes.

Carbohydrates

Structure and Classification

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, serving as a primary energy source and structural material in cells.

• Monosaccharides: Simple sugars (e.g., glucose, fructose) that vary by the number of carbon atoms and the position of the carbonyl group.

• Disaccharides: Formed by joining two monosaccharides via a glycosidic linkage.

• Polysaccharides: Long chains of monosaccharides; examples include starch, glycogen, and cellulose.

Table: Comparison of Major Polysaccharides

Polysaccharide	Monomer	Function	Structure
Starch	Glucose	Energy storage in plants	Branched/unbranched
Glycogen	Glucose	Energy storage in animals	Highly branched
Cellulose	Glucose	Structural (plant cell walls)	Unbranched, linear

• Glycosidic Linkages: Covalent bonds joining monosaccharides in polysaccharides.

• Storage vs. Structural Polysaccharides: Storage polysaccharides (starch, glycogen) are easily broken down for energy; structural polysaccharides (cellulose) provide rigidity.

Lipids

Types and Functions

Lipids are hydrophobic molecules, including fats, phospholipids, and steroids, with diverse roles in energy storage, membrane structure, and signaling.

• Fats (Triglycerides): Composed of glycerol and three fatty acids joined by ester linkages. Function as energy storage.

• Phospholipids: Contain a glycerol backbone, two fatty acids, and a phosphate group. Major component of cell membranes; amphipathic (hydrophilic head, hydrophobic tails).

• Steroids: Lipids with a characteristic four-ring structure (e.g., cholesterol, hormones).

Table: Comparison of Lipid Types

Lipid Type	Structure	Function
Fats	Glycerol + 3 fatty acids	Energy storage
Phospholipids	Glycerol + 2 fatty acids + phosphate	Membrane structure
Steroids	Four fused rings	Hormones, membrane fluidity

• Saturated vs. Unsaturated Fatty Acids: Saturated fatty acids have no double bonds; unsaturated have one or more double bonds, affecting fluidity and health impact.

• Cis vs. Trans Fatty Acids: Cis double bonds create kinks, increasing fluidity; trans double bonds result in straighter chains, associated with negative health effects.

Proteins

Structure and Function

Proteins are polymers of amino acids, performing a vast array of functions in cells, including catalysis, structure, transport, and signaling.

• Amino Acids: Building blocks of proteins, each with a central carbon, amino group, carboxyl group, hydrogen, and variable R group.

• Peptide Bonds: Covalent bonds linking amino acids in a polypeptide chain.

• Levels of Protein Structure:

  • Primary: Sequence of amino acids.

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

  • Tertiary: 3D shape formed by interactions among R groups.

  • Quaternary: Association of multiple polypeptide chains.

• Denaturation: Loss of protein structure (and function) due to environmental changes (e.g., pH, temperature).

• Protein Function: Determined by structure; includes enzymes, structural proteins, transporters, antibodies, etc.

Table: Levels of Protein Structure

Level	Description	Stabilizing Bonds
Primary	Amino acid sequence	Peptide bonds
Secondary	α-helix, β-sheet	Hydrogen bonds
Tertiary	3D folding	Hydrogen, ionic, disulfide, hydrophobic interactions
Quaternary	Multiple polypeptides	Same as tertiary

• X-ray Crystallography: Technique to determine the 3D structure of proteins and other molecules.

Nucleic Acids

Structure and Function

Nucleic acids (DNA and RNA) store, transmit, and help express hereditary information.

• Nucleotides: Monomers of nucleic acids, each consisting of a sugar, phosphate group, and nitrogenous base.

• DNA vs. RNA: DNA contains deoxyribose sugar and is double-stranded; RNA contains ribose sugar and is usually single-stranded.

• Nitrogenous Bases: Two types:

  • Pyrimidines: Cytosine, Thymine (DNA), Uracil (RNA)

  • Purines: Adenine, Guanine

• Base Pairing: In DNA, Adenine pairs with Thymine, Guanine pairs with Cytosine.

Table: DNA vs. RNA

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

• Genomics and Proteomics: The study of genomes and proteins, respectively, has transformed biological inquiry and has applications in medicine, such as fighting disease.

Additional info:

• Some explanations and examples were expanded for clarity and completeness based on standard biology curricula.