Chemical Foundations of Life: Functional Groups and Biomolecules

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Organic Molecules & Biomolecules

Definition and Importance

Organic molecules, also known as biomolecules, are compounds found in or derived from living organisms. They are primarily composed of carbon and hydrogen atoms arranged in rings or chains. These molecules form the structural and functional basis of all living things.

Organic molecules contain both carbon and hydrogen.
Examples include carbohydrates, proteins, nucleic acids, and lipids.
Inorganic molecules, such as CO2, may contain carbon but lack hydrogen bonded to it.

Ethane molecule structure CO2 molecule structure

Carbon: The Backbone of Life

Properties of Carbon

Carbon is unique in its ability to form diverse molecules due to its four valence electrons, allowing it to make four covalent bonds with other atoms. These bonds can be single or double, and carbon skeletons can be linear or form rings.

Carbon skeletons provide the framework for organic molecules.
Structural diversity arises from variations in length, branching, and ring formation.

Linear and branched carbon skeletons Ring structures of carbon skeletons Various carbon skeletons

Functional Groups

Definition and Role

Functional groups are specific groups of atoms attached to the carbon skeleton of organic molecules. They determine the chemical properties and reactivity of these molecules by participating in characteristic chemical reactions.

There are seven major functional groups in living organisms: Hydroxyl, Carbonyl, Carboxyl, Amino, Sulfhydryl, Phosphate, and Methyl.

Table of functional groups, names, and examples

Major Functional Groups

Hydroxyl (–OH): Found in alcohols; polar and forms hydrogen bonds with water.
Carbonyl (C=O): Found in ketones and aldehydes; increases molecule's reactivity.
Carboxyl (–COOH): Acts as an acid; found in amino acids and fatty acids.
Amino (–NH2): Acts as a base; found in amino acids.
Sulfhydryl (–SH): Forms disulfide bridges in proteins; found in cysteine.
Phosphate (–OPO32–): Contributes negative charge; found in ATP, DNA, and RNA.
Methyl (–CH3): Affects gene expression and molecular shape.

Hydroxyl group structure and properties Carbonyl group structure and properties Carboxyl group structure and properties Amino group structure and properties Sulfhydryl group structure and properties Phosphate group structure and properties Methyl group structure and properties

Monomers & Polymers

Building Biomolecules

Biomolecules are often polymers, large molecules made by linking together smaller units called monomers. The process of forming polymers from monomers is called polymerization.

Monomers: The repeating units that serve as building blocks for polymers.
Polymers: Long molecules consisting of many similar or identical monomers linked by covalent bonds.

Monomers and polymerization

Dehydration and Hydrolysis Reactions

Dehydration Reaction: Joins monomers by removing a molecule of water, forming a covalent bond.
Hydrolysis Reaction: Breaks polymers into monomers by adding water, breaking covalent bonds.

Dehydration reaction between monosaccharides

Classes of Biomolecules

Overview

Cells contain thousands of different biomolecules, which can be grouped into four main classes: carbohydrates, proteins, nucleic acids, and lipids. Each class has unique structures and functions essential for life.

Biomolecule cartoon overview

Carbohydrates

Structure and Types

Carbohydrates are sugars and polymers of sugars. The simplest carbohydrates are monosaccharides, which serve as monomers for more complex carbohydrates.

Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose, ribose, deoxyribose).
Disaccharides: Double sugars formed by joining two monosaccharides (e.g., sucrose, lactose, maltose).
Polysaccharides: Large polymers of monosaccharides (e.g., starch, glycogen, cellulose, chitin).

Table of monosaccharides Glucose structure Fructose structure Deoxyribose structure Galactose structure Disaccharide structures Sucrose structure Polysaccharide structure Cellulose structure Starch structure Glycogen structure Chitin structure

Functions of Carbohydrates

Fuel: Main source of energy for cellular processes (e.g., glucose for ATP production).
Building Blocks: Structural components (e.g., cellulose in plant cell walls, deoxyribose in DNA).
Cell Markers: Carbohydrates on cell surfaces serve as identification tags (e.g., blood group antigens).
Storage: Glycogen in animals (short-term), starch in plants (long-term).

DNA structure with deoxyribose Blood group antigens as cell markers Glycogen structure Starch structure Hydrolysis of carbohydrates

Proteins

Structure and Function

Proteins are the most abundant biomolecules and are essential for all living organisms. They serve as enzymes, structural components, hormones, antibodies, and more. The function of a protein is determined by its structure.

Amino acids: Monomers of proteins; 20 different types exist.
Peptide bonds: Covalent bonds linking amino acids, formed by dehydration reactions.

Amino acid structure General structure of amino acids Peptide bond formation

Levels of Protein Structure

Primary: Sequence of amino acids.
Secondary: Local folding into α-helices and β-sheets, stabilized by hydrogen bonds.
Tertiary: Overall 3D shape, stabilized by interactions among R groups (hydrophobic interactions, hydrogen bonds, ionic bonds, disulfide bridges).
Quaternary: Association of multiple polypeptide chains.

Primary structure Secondary structure Tertiary structure Quaternary structure Protein folding Protein structure overview Primary structure example Secondary structure example Secondary structure types Tertiary structure interactions Disulfide bridge in tertiary structure Quaternary structure example Quaternary structure example 2 Important quaternary proteins Misfolded protein diseases Sickle cell anemia protein structure Denatured protein Renatured protein Protein denaturation Protein denaturation and renaturation

Nucleic Acids

DNA and RNA

Nucleic acids are polymers that store and transmit genetic information. The two main types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). DNA stores genetic information, while RNA is involved in protein synthesis and gene regulation.

Nucleotides: Monomers of nucleic acids, each consisting of a 5-carbon sugar, a phosphate group, and a nitrogenous base.
Polynucleotides: Polymers of nucleotides.

DNA and RNA cartoon DNA structure Nucleotide structure Nitrogenous bases Sugars in nucleic acids Antiparallel DNA strands DNA double helix and RNA single strand DNA replication and Okazaki fragments Complementary base pairing DNA packaging in cells Genes in DNA Chromosomes

ATP (Adenosine Triphosphate)

Structure and Function

ATP is the primary energy carrier in cells. It consists of adenine, ribose sugar, and three phosphate groups. Hydrolysis of ATP releases energy for cellular processes.

ATP structure ATP molecule

Lipids

Structure and Types

Lipids are hydrophobic molecules that do not form polymers. They include fats, phospholipids, steroids, waxes, and pigments. Lipids serve as energy storage, structural components of cell membranes, and signaling molecules (hormones).

Fats (Triglycerides): Composed of glycerol and three fatty acids; used for long-term energy storage.
Phospholipids: Glycerol, two fatty acids, and a phosphate group; major component of cell membranes.
Steroids: Four fused carbon rings; include cholesterol and hormones.

Lipid cartoon Types of lipids

Triglycerides

Saturated fatty acids: No double bonds; solid at room temperature (e.g., butter).
Unsaturated fatty acids: One or more double bonds; liquid at room temperature (e.g., olive oil).
Polyunsaturated fatty acids: Multiple double bonds.

Polyunsaturated fatty acid structure Saturated fat example Saturated fat example 2 Saturated fat example 3 Unsaturated fat example Unsaturated fat example 2 Triglyceride formation Fat storage in humans Fat-soluble vitamins and hormones

Phospholipids and Membranes

Phospholipids form the basic structure of cell membranes, arranging themselves into bilayers with hydrophilic heads facing outward and hydrophobic tails inward. This arrangement is critical for membrane function and integrity.

Steroids and Cholesterol

Steroids: Lipids with four fused rings; include hormones like estrogen, testosterone, and cortisol.
Cholesterol: Essential for membrane structure but excess can lead to health issues.

Cholesterol structure Steroid hormone effects Cortisol structure

Additional info: This guide covers the chemical foundations of life, focusing on the structure and function of organic molecules, functional groups, and the four major classes of biomolecules. It provides foundational knowledge for further study in cell biology, metabolism, and molecular genetics.