Structure and Function of Large Biological Molecules (Chapter 5 Study Guide)

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Structure and Function of Large Biological Molecules

Macromolecules: Polymers and Monomers

Macromolecules are large, complex molecules essential for life, including carbohydrates, proteins, and nucleic acids. These are polymers, built from repeating units called monomers. Lipids, though vital, are not true polymers.

Polymer: A long molecule consisting of many similar or identical building blocks (monomers).
Monomer: The repeating unit that serves as a building block for polymers.
Dehydration Reaction: Joins two monomers by removing a water molecule.
Hydrolysis: Breaks polymers into monomers by adding water.
Enzymes: Biological catalysts that facilitate these reactions.

Four classes of biological molecules Dehydration and hydrolysis reactions

Additional info: The diversity of macromolecules arises from the variety of monomers and their arrangements.

Carbohydrates: Structure and Function

Carbohydrates are compounds containing carbon, hydrogen, and oxygen, and serve as fuel and building material. They include sugars (monosaccharides) and polymers of sugars (polysaccharides).

Monosaccharides: Simple sugars, such as glucose, ribose, and fructose. They are classified by the location of the carbonyl group (aldose or ketose) and the number of carbon atoms.
Disaccharides: Formed by joining two monosaccharides via a dehydration reaction, creating a glycosidic linkage.
Polysaccharides: Polymers of monosaccharides with storage (starch, glycogen) or structural (cellulose, chitin) roles.

Glucose structure Carbonyl group: ketone and aldehyde Classification of monosaccharides Carbohydrate structure: glucose and ribose Linear and ring forms of glucose Alpha and beta glucose ring structures Formation of disaccharide (glycosidic linkage) Important disaccharides: maltose and sucrose Polysaccharide structures: starch, glycogen, cellulose Cellulose structure and microfibrils Alpha and beta glucose linkages Chitin structure and function

Starch: Storage polysaccharide in plants, composed of alpha glucose monomers.
: Storage polysaccharide in animals, highly branched.
Cellulose: Structural polysaccharide in plant cell walls, composed of beta glucose monomers.
Chitin: Structural polysaccharide in arthropod exoskeletons and fungal cell walls.

Additional info: Humans can digest starch but not cellulose due to enzyme specificity for alpha linkages.

Lipids: Structure and Function

Lipids are hydrophobic molecules, including fats, phospholipids, and steroids. They are not polymers but are essential for energy storage, membrane structure, and signaling.

Fats: Constructed from glycerol and fatty acids. Three fatty acids join glycerol via ester linkages to form triglycerides.
Saturated fats: No double bonds; solid at room temperature (animal fats).
Unsaturated fats: One or more double bonds; liquid at room temperature (plant and fish oils).
Phospholipids: Two fatty acids and a phosphate group attached to glycerol; form cell membranes.
Steroids: Lipids with four fused rings; cholesterol is a key example.

Fat molecule and adipose cell Fat molecule structure Saturated and unsaturated fats Adipose cell and fat droplets Phospholipid structure Phospholipid bilayer in cell membrane Steroid structure: cholesterol Estradiol and testosterone: functional group differences

Additional info: Phospholipids self-assemble into bilayers, forming the basis of biological membranes.

Proteins: Structure and Function

Proteins are polymers of amino acids and account for more than 50% of the dry mass of most cells. They perform diverse functions, including catalysis, defense, transport, communication, movement, and structural support.

Amino acids: Organic molecules with carboxyl and amino groups; differ by their side chains (R groups).
Peptide bond: Covalent bond joining amino acids in a polypeptide.
Polypeptide: Polymer of amino acids; proteins may consist of one or more polypeptides.
Protein structure: Four levels—primary (sequence), secondary (coils/folds), tertiary (3D shape), quaternary (multiple polypeptides).
Denaturation: Loss of protein structure due to environmental changes; results in loss of function.

Protein functions Amino acid structure Amino acid side chains: nonpolar, polar, charged Peptide bond formation Protein folding and structure Normal and denatured protein Primary structure: amino acid sequence Secondary structure: alpha helix and beta sheet Tertiary structure: interactions among side chains

Additional info: Protein folding is assisted by chaperonins; misfolded proteins are linked to diseases such as Alzheimer's and Parkinson's.

Nucleic Acids: Structure and Function

Nucleic acids store, transmit, and help express hereditary information. DNA and RNA are polymers of nucleotides, each consisting of a nitrogenous base, a pentose sugar, and a phosphate group.

DNA: Double-stranded helix; stores genetic information.
RNA: Single-stranded; involved in protein synthesis.
Nucleotide: Monomer of nucleic acids; composed of a nucleoside (base + sugar) and a phosphate group.
Phosphodiester linkage: Joins nucleotides in a polynucleotide chain.
Complementary base pairing: A-T and G-C in DNA; A-U and G-C in RNA.
Gene expression: DNA → RNA → protein.

Additional info: Genomics and proteomics analyze large sets of genes and proteins, transforming biological research and evolutionary studies.

Summary Table: Macromolecules

Class	Monomer	Polymer	Main Function
Carbohydrates	Monosaccharide	Polysaccharide	Energy storage, structure
Proteins	Amino acid	Polypeptide	Catalysis, structure, transport, defense
Nucleic Acids	Nucleotide	Polynucleotide	Information storage and transmission
Lipids	Fatty acid, glycerol	Not true polymers	Energy storage, membranes, signaling