BackThe Chemistry of Organic Molecules: Structure and Function
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The Chemistry of Organic Molecules
Introduction to Organic Molecules
Organic molecules are the chemical compounds that form the basis of life. They are primarily composed of carbon atoms bonded with hydrogen, oxygen, nitrogen, and other elements. The unique properties of carbon allow for the formation of a wide variety of complex molecules essential for biological processes.
Organic molecules include carbohydrates, lipids, proteins, and nucleic acids.
These molecules are often built from smaller subunits called monomers, which join to form polymers.
Functional groups attached to carbon skeletons determine the chemical reactivity and properties of organic molecules.
Functional Groups in Organic Molecules
Key Functional Groups and Their Properties
Functional groups are specific groups of atoms within molecules that have characteristic properties and chemical reactivity. They play a crucial role in the structure and function of organic molecules.
Group | Structure | Compound | Significance |
|---|---|---|---|
Hydroxyl | R–OH | Alcohol (e.g., ethanol) | Polar, forms hydrogen bonds; present in sugars, some amino acids |
Carbonyl | R–C=O | Aldehyde (e.g., formaldehyde), Ketone (e.g., acetone) | Polar; present in sugars |
Carboxyl (acidic) | R–COOH | Carboxylic acid (e.g., acetic acid) | Polar, acidic; present in fatty acids, amino acids |
Amino | R–NH2 | Amine (e.g., tryptophan) | Polar, basic, forms hydrogen bonds; present in amino acids |
Sulfhydryl | R–SH | Thiol (e.g., ethanethiol) | Forms disulfide bonds; present in some amino acids |
Phosphate | R–O–PO3H2 | Organic phosphate (e.g., in phosphorylated molecules) | Polar, acidic; present in nucleotides, phospholipids |
Biological Macromolecules
Categories, Monomers, and Polymers
Biological macromolecules are large molecules necessary for life, built from smaller organic molecules. Each category has characteristic monomers and polymers.
Category | Subunits (Monomers) | Polymer |
|---|---|---|
Carbohydrates | Monosaccharide | Polysaccharide |
Lipids | Glycerol and fatty acids | Does not form polymers |
Proteins | Amino acids | Polypeptide |
Nucleic acids | Nucleotide | DNA, RNA |
Monomers are the building blocks of polymers.
Polymers are large molecules made by joining many monomers together.
Carbohydrates
Monosaccharides and Isomers
Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically with the formula (CH2O)n. They serve as energy sources and structural components in cells.
Monosaccharides are simple sugars, such as glucose, fructose, and galactose.
Isomers are molecules with the same molecular formula but different structures. For example, glyceraldehyde (an aldehyde) and dihydroxyacetone (a ketone) are isomers with the formula C3H6O3.
Compound | Structure |
|---|---|
Glyceraldehyde | CHO–CHOH–CH2OH |
Dihydroxyacetone | CH2OH–CO–CH2OH |
Polysaccharides are long chains of monosaccharides linked by glycosidic bonds, serving as energy storage (e.g., starch, glycogen) or structural support (e.g., cellulose, chitin).
Proteins
Amino Acids and Peptide Bonds
Proteins are polymers of amino acids, which are linked by peptide bonds. Each amino acid contains an amino group, a carboxyl group, a hydrogen atom, and a variable R group attached to a central carbon.
Amino acid structure:
Peptide bond formation: A dehydration reaction links the carboxyl group of one amino acid to the amino group of another, releasing water.
Example: The sequence and composition of amino acids determine a protein's structure and function.
Lipids
Structure and Function
Lipids are a diverse group of hydrophobic molecules, including fats, oils, phospholipids, and steroids. They are not true polymers but are assembled from smaller molecules.
Fats and oils are composed of glycerol and fatty acids. They serve as long-term energy storage and insulation.
Phospholipids are major components of cell membranes, consisting of two fatty acids, a glycerol, and a phosphate group.
Steroids (e.g., cholesterol, testosterone) have a structure of four fused carbon rings and function as hormones or membrane components.
Example: The kink in unsaturated fatty acids (due to double bonds) prevents tight packing, making oils liquid at room temperature.
Nucleic Acids
DNA and RNA
Nucleic acids store and transmit genetic information. They are polymers of nucleotides, each consisting of a phosphate group, a pentose sugar, and a nitrogenous base.
DNA (deoxyribonucleic acid) stores genetic information in cells.
RNA (ribonucleic acid) is involved in protein synthesis and gene regulation.
Example: The sequence of nucleotides in DNA encodes the instructions for building proteins.
Polymerization and Dehydration Synthesis
Formation of Biological Polymers
Polymers are formed by joining monomers through dehydration synthesis (condensation reaction), which removes a water molecule for each bond formed.
Dehydration synthesis:
Hydrolysis: The reverse process, where water is added to break bonds between monomers.
Example: The formation of a disaccharide from two monosaccharides involves the removal of a water molecule.
Additional info: Some images referenced in the original material (e.g., animal and plant cells, red blood cells, lions) illustrate the diversity of life forms that rely on organic molecules for structure and function.
