Biological Molecules: Structure and Function (General Biology Study Notes)

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Chapter 3: Biological Molecules

Introduction

Biological molecules are essential for life, forming the basis of cellular structure and function. This chapter explores the chemistry of life, focusing on the major classes of biological molecules: carbohydrates, proteins, nucleic acids, and lipids.

Why Is Carbon So Important in Biological Molecules?

Organic vs. Inorganic Molecules

Biological molecules are defined as all molecules produced by living things.
Most biological molecules are organic, meaning they contain carbon and usually hydrogen and oxygen.
Inorganic molecules generally lack carbon atoms and are simpler than organic molecules.

Bonding Properties of Carbon

The bonding properties of carbon are key to the complexity of organic molecules.
Carbon atoms have four outer shell electrons and tend to form four covalent bonds, allowing for a variety of molecular structures.
Atoms with partially filled outer electron shells tend to react with one another, sharing electrons to achieve stability.

Common Elements in Biological Molecules

The most commonly found elements in biological molecules are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N).
These elements bond in specific ways, enabling the diversity of life on Earth.

Functional Groups

Functional groups are specific atoms or groups of atoms attached to the carbon backbone of organic molecules.
They are generally more reactive than the carbon backbone and determine the chemical properties of the molecule.
Examples include hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), and phosphate (-PO4).

How Are Large Biological Molecules Synthesized?

Monomers and Polymers

Large biological molecules are formed by joining smaller subunits called monomers.
Chains of monomers are called polymers.

Dehydration Synthesis and Hydrolysis

Dehydration synthesis is the process by which monomers are joined to form polymers, with the removal of a water molecule.
Hydrolysis is the reverse reaction, breaking polymers into monomers by adding water.

Equation (Dehydration Synthesis):

Equation (Hydrolysis):

Four Major Classes of Biological Molecules

Carbohydrates
Proteins
Nucleotides/Nucleic Acids
Lipids

What Are Carbohydrates?

Structure and Types

Composed of carbon, hydrogen, and oxygen in a ratio of approximately 1:2:1.
Monosaccharides: Single sugar units (e.g., glucose, fructose, galactose, ribose, deoxyribose).
Disaccharides: Two monosaccharides joined by dehydration synthesis (e.g., sucrose, lactose, maltose).
Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose, chitin).

General formula for carbohydrates:

Functions and Examples

Energy storage: Starch (plants), glycogen (animals).
Structural support: Cellulose (plant cell walls), chitin (exoskeletons of arthropods, fungal cell walls).
Short-term energy: Disaccharides like sucrose and lactose.

What Are Proteins?

Structure and Diversity

Proteins are polymers of amino acids, joined by peptide bonds via dehydration synthesis.
There are 20 different amino acids, each with a unique R group that determines its properties (hydrophilic, hydrophobic, acidic, basic).

Levels of Protein Structure

Primary structure: Sequence of amino acids.
Secondary structure: Hydrogen bonding forms alpha-helices and beta-pleated sheets.
Tertiary structure: 3D folding due to interactions among R groups.
Quaternary structure: Association of multiple polypeptide chains.

Functions of Proteins

Structural: Keratin, collagen.
Movement: Actin, myosin.
Defense: Antibodies.
Storage: Albumin.
Signaling: Insulin.
Enzymatic: Amylase, lipase.

Denaturation

Loss of protein's three-dimensional structure, resulting in loss of function.
Can be caused by heat, pH changes, or chemicals.

What Are Nucleotides and Nucleic Acids?

Structure of Nucleotides

Each nucleotide consists of a five-carbon sugar (ribose or deoxyribose), a phosphate group, and a nitrogenous base.
Nitrogenous bases: Pyrimidines (single ring: thymine, uracil, cytosine), Purines (double ring: adenine, guanine).

Functions of Nucleotides

Energy carriers: ATP (adenosine triphosphate).
Intracellular messengers.
Subunits of nucleic acids: DNA and RNA.

Nucleic Acids

DNA (deoxyribonucleic acid): Double-stranded helix, stores genetic information.
RNA (ribonucleic acid): Single-stranded, involved in protein synthesis.

Equation (Nucleotide Polymerization):

What Are Lipids?

General Properties

Lipids are hydrophobic molecules, insoluble in water, and not formed by linking monomers into polymers.
Major functions: energy storage, waterproofing, membrane structure, hormones.

Major Groups of Lipids

Fats and oils: Composed of fatty acids and glycerol (triglycerides). Fats are solid at room temperature (saturated), oils are liquid (unsaturated).
Waxes: Highly saturated, water-repellent, found in plant leaves, bird feathers, and honeycomb.
Phospholipids: Have hydrophilic heads and hydrophobic tails, form the bilayer of cell membranes.
Steroids: Four fused carbon rings, include cholesterol, estrogen, testosterone.

Comparison Table: Four Principal Classes of Biological Molecules

Class	Monomer/Subunit	Polymer/Structure	Main Function	Examples
Carbohydrates	Monosaccharide	Polysaccharide	Energy storage, structure	Glucose, starch, cellulose
Proteins	Amino acid	Polypeptide	Enzymes, structure, transport	Hemoglobin, amylase, keratin
Nucleic Acids	Nucleotide	DNA/RNA	Genetic information, energy transfer	DNA, RNA, ATP
Lipids	Fatty acid, glycerol	Triglyceride, phospholipid, steroid	Energy storage, membranes, hormones	Fats, oils, cholesterol

Additional info:

Prions are infectious proteins that can cause diseases such as mad cow disease by altering the shape of normal proteins in the brain.
Denaturation of proteins can be reversible or irreversible, depending on the conditions.
Phospholipids are amphiphilic, meaning they have both hydrophilic and hydrophobic regions, which is critical for membrane structure.