Lecture 3 Study Guide: Biological Macromolecules and Their Properties

Biological Macromolecules: Structure, Function, and Properties

Introduction

This study guide covers the major classes of biological macromolecules—carbohydrates, proteins, nucleic acids, and lipids—focusing on their structure, function, and the chemical principles underlying their behavior in living systems. Understanding these molecules is fundamental to the study of biology.

Carbohydrates

Monomer Subunits

• Monosaccharides (simple sugars, e.g., glucose, fructose)

Bond Types and Linkages

• Glycosidic bonds (α or β linkages) connect monosaccharides to form disaccharides and polysaccharides.

Characteristics

• Can be linear or branched polymers (e.g., starch vs. cellulose)

• Structural diversity arises from different monosaccharide combinations and glycosidic linkages.

Functions

• Energy storage (e.g., glycogen, starch)

• Structural support (e.g., cellulose in plants, chitin in fungi and arthropods)

Proteins

Monomer Subunits

• Amino acids (20 standard types)

Bond Types and Structure

• Peptide bonds link amino acids into polypeptide chains.

• Four levels of structure: primary, secondary, tertiary, quaternary.

• Bonds involved: hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic interactions.

Characteristics

• Structure determines function.

• Shape can be disrupted (denatured) by changes in pH, temperature, or chemicals.

Functions

• Enzymatic catalysis, structural support, transport, signaling, movement, defense.

Nucleic Acids

Monomer Subunits

• Nucleotides (composed of a sugar, phosphate group, and nitrogenous base)

Bond Types and Structure

• Phosphodiester bonds link nucleotides in a sugar-phosphate backbone.

• Directionality: built 5' to 3'.

• Complementary base pairing via hydrogen bonds (A-T/U, G-C).

Characteristics

• DNA: double-stranded, stable, stores genetic information.

• RNA: single-stranded, various functions (messenger, catalytic, regulatory).

Functions

• Information storage and transfer, catalysis (ribozymes), regulation.

Lipids

Monomer Subunits

• Not true polymers; composed of fatty acids, glycerol, and other components.

Bond Types and Structure

• Ester bonds (in triglycerides), hydrophobic interactions in membranes.

Characteristics

• Amphipathic (e.g., phospholipids), hydrophobic, can be saturated or unsaturated.

Functions

• Energy storage, membrane structure, signaling molecules (steroids, hormones).

Protein Structure and Function

Levels of Protein Structure

• Primary structure: sequence of amino acids.

• Secondary structure: α-helices and β-sheets formed by hydrogen bonding.

• Tertiary structure: 3D folding due to side chain interactions.

• Quaternary structure: association of multiple polypeptide chains.

Disruption of Protein Structure

• Denaturation: loss of 3-D shape due to heat, pH, or chemicals.

• Loss of structure leads to loss of function.

Amino Acid Functional Groups

• Four categories: nonpolar, polar uncharged, acidic (negatively charged), basic (positively charged).

• Chemical properties affect protein folding and function.

Nucleic Acids: Structure and Polarity

• Polarity: 5' phosphate end to 3' hydroxyl end.

• Directionality is essential for replication and transcription.

Comparison Table: Major Biomolecules

Biopolymer	Monomer Subunits	Bond Types & Location or Linkage	Characteristics	Functions
Carbohydrates	Monosaccharides	Glycosidic bonds (α or β)	Linear or branched, hydrophilic	Energy storage, structure
Proteins	Amino acids	Peptide bonds	Four levels of structure, diverse shapes	Enzymes, structure, transport, signaling
Nucleic Acids	Nucleotides	Phosphodiester bonds	DNA double helix, RNA single-stranded	Genetic information, catalysis
Lipids	Fatty acids, glycerol	Ester bonds, hydrophobic interactions	Amphipathic, hydrophobic, variable saturation	Membranes, energy storage, signaling

Key Terms and Definitions

• Polymer: Large molecule made of repeating subunits (monomers).

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

• Polymerization: Chemical process of joining monomers to form a polymer.

• Hydrolysis: Breaking a bond by adding water.

• Condensation (Dehydration): Forming a bond by removing water.

• Saccharide: Sugar molecule.

• α & β Glycosidic Bonds: Types of linkages between monosaccharides.

• Peptide Bond: Covalent bond linking amino acids in proteins.

• Disulfide Bridge: Covalent bond between sulfur atoms in cysteine residues, stabilizing protein structure.

• Phosphodiester Bond: Covalent bond linking nucleotides in nucleic acids.

• Amphipathic: Molecule with both hydrophilic and hydrophobic regions (e.g., phospholipids).

• Saturated/Unsaturated: Refers to presence or absence of double bonds in fatty acids.

Example: Protein Denaturation

• When an egg is cooked, heat disrupts the hydrogen bonds and noncovalent interactions in egg white proteins, causing them to unfold and aggregate (denature), changing from clear to white.

Example: DNA Structure

• DNA is a double helix with antiparallel strands held together by complementary base pairing (A-T, G-C) via hydrogen bonds.

Additional info:

• Understanding the structure and function of macromolecules is foundational for topics such as metabolism, genetics, and cell biology.