3.1 Carbon Atoms and Molecular Diversity

CHNOPS: Essential Elements in Living Things

Living organisms are primarily composed of six major elements, remembered by the mnemonic CHNOPS: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, and Sulfur. These elements form the basis of most biological molecules.

• Carbon is unique in its ability to form four covalent bonds, allowing for a diversity of stable compounds.

• These elements are essential for the structure and function of cells and organisms.

• Example: CHNOPS are found in DNA, proteins, carbohydrates, and lipids.

Definition of "Organic" in Science

Organic compounds are defined by the presence of carbon and hydrogen bonds and their synthesis by living cells.

• Organic compounds must contain carbon and at least one carbon-hydrogen bond, and are made by cells.

• The simplest organic molecule is methane ().

• Inorganic compounds may contain carbon but lack carbon-hydrogen bonds or are not made by cells (e.g., , carbon monoxide).

• Examples: Glucose () is organic; carbon dioxide () is inorganic.

Structure and Properties of Carbon Compounds

Bonding and Molecular Geometry

Carbon atoms form four covalent bonds, resulting in a tetrahedral geometry with bond angles of approximately 109.5°.

• Carbon's four valence electrons allow for single, double, or triple covalent bonds.

• Carbon skeletons can vary in length, branching, double bond position, and ring formation.

Example: Methane () has a tetrahedral structure.

Variation in Carbon Skeletons

Carbon chains can differ in several ways, contributing to molecular diversity.

• Length: Chains may be short (ethane) or long (propane).

• Branching: Chains may be straight (butane) or branched (2-methylpropane).

• Double Bond Position: Double bonds can be located at different positions (1-butene vs. 2-butene).

• Presence of Rings: Some molecules form rings (cyclohexane, benzene).

Isomerism in Organic Molecules

Types of Isomers

Isomers are compounds with the same molecular formula but different structures and properties.

• Structural Isomers: Differ in covalent arrangement of atoms (e.g., pentane vs. 2-methylbutane).

• Cis-trans Isomers (Geometric Isomers): Differ in spatial arrangement around a double bond. Cis means atoms are on the same side; trans means on opposite sides.

• Enantiomers: Isomers that are mirror images of each other, differing in spatial arrangement around an asymmetric carbon.

Example: L- and D- forms of amino acids are enantiomers.

Adenosine Triphosphate (ATP): Cellular Energy Currency

Structure and Function of ATP

Adenosine triphosphate (ATP) is the primary energy carrier in cells, used for various cellular activities.

• ATP consists of adenine, ribose, and three phosphate groups.

• Energy is released when ATP is hydrolyzed to adenosine diphosphate (ADP) and inorganic phosphate ():

• ATP is used for making large molecules, active transport, and movement within cells.

• ATP is unstable and not stored long-term; energy is stored as starch (plants), glycogen (animals), and fats.

Macromolecules: Structure, Function, and Examples

Overview of Macromolecules

Macromolecules are large, complex molecules essential for life. They are typically polymers made from smaller monomer units.

Macromolecules as Polymers

Most macromolecules are polymers, built from monomers joined by covalent bonds.

• Polymerization: Process of joining monomers to form polymers.

• Carbohydrates: Monosaccharides joined by glycosidic bonds to form disaccharides or polysaccharides.

• Proteins: Amino acids joined by peptide bonds to form polypeptides.

• Nucleic Acids: Nucleotides joined by phosphodiester bonds to form DNA or RNA.

Example: Starch is a polysaccharide formed from glucose monomers.

Bond Formation in Macromolecules

• Peptide bond: Joins amino acids in proteins.

• Glycosidic bond: Joins monosaccharides in carbohydrates.

• Phosphodiester bond: Joins nucleotides in nucleic acids.

Summary Table: Macromolecule Bonds

Additional info: Lipids are not true polymers, as they are not formed by repetitive monomer units, but are essential for cell membranes and energy storage.