Chapter 4: Carbon and the Molecular Diversity of Life

Organic Chemistry and Organic Compounds

Organic chemistry is the study of carbon-containing compounds, which are fundamental to all living organisms. Organic compounds are molecules that contain carbon atoms bonded to other elements, typically hydrogen, oxygen, nitrogen, and sometimes sulfur and phosphorus.

• Basic Characteristics of Organic Compounds: Organic compounds are characterized by the presence of carbon atoms, often arranged in chains or rings. They are typically associated with living organisms.

• Common Elements in Organic Compounds: The primary elements found in organic compounds are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). Secondary elements include sulfur (S) and phosphorus (P).

• Properties of Carbon Atoms: Carbon atoms have four valence electrons, allowing them to form four covalent bonds with other atoms. This versatility enables carbon to create a wide variety of molecular structures.

• Major vs. Secondary Elements: Major elements (C, H, O, N) are essential for life, while secondary elements (S, P) play specialized roles in biological molecules.

Example: Glucose (C6H12O6) is an organic compound essential for cellular energy.

Carbon Structures and Isomers

Carbon atoms can bond with each other to form diverse structures, including chains, rings, and branched molecules. The arrangement of these atoms determines the properties and functions of the resulting compounds.

• Types of Carbon Structures:

  • Chains: Linear arrangements of carbon atoms.

  • Rings: Cyclic structures formed by carbon atoms.

  • Branches: Carbon chains with side groups.

• Valence Rules: Carbon forms four covalent bonds, which can be single, double, or triple bonds. The number of bonds determines the molecule's shape and reactivity.

• Hydrocarbons: Molecules consisting only of carbon and hydrogen. Examples include methane (CH4), ethane (C2H6), and benzene (C6H6).

• Isomers: Compounds with the same molecular formula but different structures. There are three main types:

  • Structural Isomers: Differ in the covalent arrangement of atoms.

  • Cis-trans Isomers: Differ in spatial arrangement around a double bond.

  • Enantiomers: Mirror images of each other, differing in spatial arrangement around an asymmetric carbon.

• Structure Determines Function: The specific arrangement of atoms in a molecule influences its chemical properties and biological function.

Example: Butane and isobutane are structural isomers with different physical properties.

Functional Groups and ATP

Functional groups are specific groups of atoms attached to the carbon skeleton of organic molecules, conferring distinct chemical properties. ATP (adenosine triphosphate) is a key molecule in cellular energy transfer.

• Seven Most Common Functional Groups:

  Name	Structure	Properties
  Hydroxyl	-OH	Alcohols; polar, forms hydrogen bonds
  Carbonyl	>C=O	Ketones (within carbon skeleton), aldehydes (end of skeleton); polar
  Carboxyl	-COOH	Carboxylic acids; acidic, can donate H+
  Amino	-NH2	Amines; basic, can accept H+
  Sulfhydryl	-SH	Thiols; forms disulfide bonds in proteins
  Phosphate	-OPO32-	Organic phosphates; contributes negative charge, energy transfer
  Methyl	-CH3	Methylated compounds; affects gene expression

• Naming Organic Compounds: Alcohols contain hydroxyl groups (e.g., ethanol), ketones have carbonyl groups within the skeleton (e.g., acetone), aldehydes have carbonyl groups at the end (e.g., formaldehyde), and methylated compounds have methyl groups attached.

• ATP Structure: ATP consists of an adenosine molecule (adenine + ribose) attached to three phosphate groups. The bonds between phosphate groups store energy.

  • Importance of ATP: ATP is the primary energy carrier in cells, used in metabolic processes.

Example: The hydrolysis of ATP releases energy for cellular work.

ATP Hydrolysis Equation:

Additional info: Functional groups are critical in determining the reactivity and interactions of organic molecules, influencing biological processes such as enzyme activity and gene regulation.