Chemistry in Biology: Biological Molecules and Their Formation

Chemistry in Biology

Introduction

Understanding the chemistry of biological molecules is fundamental to the study of life. Biological systems rely on the formation, structure, and function of molecules, many of which are large and complex. This section introduces the chemical principles underlying biological macromolecules.

What is a Molecule?

Definition and Importance

• Molecule: Two or more atoms held together by various forces or bonds.

• Life requires the formation of very large molecules, essential for biological structure and function.

Elements and Compounds

Basic Chemical Concepts

• Matter is made up of elements.

• Element: A substance that cannot be broken down to other substances by chemical reactions.

• Compound: A substance consisting of two or more elements in a fixed ratio.

Vocabulary: Chemical Bonds and Solutions

Term	Definition
Chemical Bonds	Forces that hold atoms together in a molecule
Covalent Bond	Chemical bond in which electrons are shared
Ionic Bond	Chemical bond between ions, one or more electrons have been transferred
Hydrogen Bond	Chemical bond in which a hydrogen is shared between two electronegative atoms (usually O and/or N)
Solute	A molecule dissolved in a liquid
Solvent	The liquid in which the molecule is dissolved

Organic Compounds

Definition and Biological Importance

• Compounds that contain carbon are called organic.

• Organic molecules are abundant in living organisms.

• Macromolecules are large organic molecules essential for life.

Formation of Biological Macromolecules

Monomers and Polymers

• Many biological molecules are formed from simple subunits called monomers linked together to form polymers.

• Polymerization requires enzymes and added energy; polymers do not form spontaneously.

How Are Macromolecules Formed?

Condensation (Dehydration) and Hydrolysis Reactions

• Condensation (Dehydration) Reaction: Two monomers bond together through the loss of a water molecule.

• Hydrolysis: Separates monomers by adding water, breaking the bond between them.

Equations:

• Dehydration: $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + H_2O$

• Hydrolysis: $\text{Polymer} + H_2O \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

Major Types of Organic Molecules and Macromolecules

Classification

• Carbohydrates: Sugars and polymers of sugars

• Lipids: Nonpolar molecules, including fats, phospholipids, and steroids

• Proteins: Polymers of amino acids

• Nucleic Acids: DNA and RNA, polymers of nucleotides

Carbohydrates

Structure and Types

• Include sugars and polymers of sugars.

• The simplest carbohydrates are monosaccharides (simple sugars).

• Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks.

• Types: Monosaccharides, Disaccharides, Polysaccharides

Monosaccharides

• Simplest sugars; one sugar unit.

• Most common are 5-carbon (pentoses) or 6-carbon (hexoses) sugars.

• Examples: Ribose ($C_5H_{10}O_5$), Deoxyribose ($C_5H_{10}O_4$), Glucose ($C_6H_{12}O_6$)

Disaccharides

• Composed of two monosaccharides joined by dehydration or condensation reaction.

• Broken apart by hydrolysis.

• Examples: Sucrose, Maltose, Lactose

Polysaccharides

• Many monosaccharides linked together to form long polymers.

• Examples:

  • Energy storage: Starch, Glycogen

  • Structural: Cellulose, Chitin

Lipids

Structure and Function

• Composed predominantly of hydrogen and carbon atoms.

• Nonpolar and very insoluble in water.

• Consist mostly of hydrocarbon regions.

• Major types: Fats, Phospholipids, Steroids

Proteins

Structure and Function

• Made up of amino acids.

• The sequence of amino acids determines a protein’s three-dimensional structure.

• There are 20 different amino acids, each with a unique side chain (R group).

• Amino acids differ in their properties due to differing R groups (side chains).

Amino Acid Structure

• All amino acids have a central (alpha) carbon, an amino group, a carboxylic acid group, a hydrogen atom, and an R group.

• The R group determines the identity and properties of the amino acid.

From Amino Acid to Protein

• Amino acids are linked by covalent peptide bonds to form polypeptides (proteins).

• Polymerization occurs via condensation (dehydration) reactions; hydrolysis breaks down polymers into monomers.

Summary Table: Types of Biological Macromolecules

Macromolecule	Monomer	Bond Type	Examples
Carbohydrates	Monosaccharide	Glycosidic linkage	Starch, Cellulose, Glycogen
Proteins	Amino acid	Peptide bond	Enzymes, Hemoglobin
Nucleic Acids	Nucleotide	Phosphodiester bond	DNA, RNA
Lipids	Fatty acids, Glycerol	Ester bond	Fats, Phospholipids, Steroids

Additional info: This summary covers foundational chemistry concepts in biology, including the structure and formation of biological macromolecules, and is suitable for introductory college-level biology courses.