뒤로Biological Molecules: Structure, Function, and Types
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Biological Molecules
Introduction to Organic Molecules
Aside from water, most biologically important molecules contain carbon. These organic molecules are essential for life and are characterized by the presence of carbon atoms bonded in various configurations. The versatility of carbon allows for the formation of a wide variety of complex molecules necessary for biological processes.
Organic molecules: Molecules containing carbon (excluding certain simple carbon compounds like CO2, CO, graphite, diamonds, and coal).
Living organisms can synthesize organic molecules.
Carbon atoms have a valence of 4, allowing them to form up to four covalent bonds with other atoms.
This bonding versatility enables the formation of diverse molecular structures.
Functional Groups in Organic Molecules
Functional groups are specific groups of atoms attached to the carbon skeleton of organic molecules. They confer distinct chemical and physical properties and are often the sites of chemical reactivity.
Functional groups behave consistently across different molecules.
They determine the chemical properties and reactivity of organic molecules.
There are seven general functional groups commonly found in biological molecules:
Functional Group | Structure | Properties | Example(s) |
|---|---|---|---|
Hydroxyl | -OH | Polar; involved in condensation and hydrolysis reactions | Alcohols (e.g., ethanol) |
Carbonyl | -C=O | Polar; forms aldehydes (terminal) or ketones (internal) | Glucose (aldehyde), acetone (ketone) |
Carboxyl | -COOH | Polar; acidic (can donate a proton); involved in peptide bonds | Amino acids, fatty acids |
Amino | -NH2 | Polar; acts as a weak base; involved in peptide bonds | Amino acids |
Sulfhydryl | -SH | Nonpolar; stabilizes protein structure | Cysteine (amino acid) |
Phosphate | -PO4 | Polar; acidic; links nucleotides; important in energy transfer | ATP, DNA, RNA |
Methyl | -CH3 | Nonpolar; increases hydrophobicity | Methylated DNA |
Synthesizing Organic Molecules: Monomers and Polymers
Monomers and Polymers
Biological macromolecules are often constructed from smaller subunits called monomers. When monomers are linked together, they form polymers, which are long chains of repeating units.
Monomer: A small molecule that can join with others to form a polymer.
Polymer: A large molecule composed of repeating monomer units.
Dehydration Synthesis and Hydrolysis
Dehydration synthesis (condensation reaction): The process by which two monomers are covalently bonded together with the removal of a water molecule.
One monomer loses a hydroxyl group (-OH), and the other loses a hydrogen atom (-H).
Hydrolysis: The process of breaking a covalent bond between two monomers by adding a water molecule.
One monomer gains a hydroxyl group (-OH), and the other gains a hydrogen atom (-H).
Example: The formation of a peptide bond between two amino acids involves dehydration synthesis, while the breakdown of a disaccharide into monosaccharides involves hydrolysis.
Classes of Biological Macromolecules
Overview of Macromolecule Classes
There are four major classes of biological macromolecules, each with distinct monomers, polymers, and functions.
Macromolecule Class | Monomer | Polymer | Examples |
|---|---|---|---|
Carbohydrates | Monosaccharides | Disaccharides, Polysaccharides | Glucose, Sucrose, Starch, Glycogen, Cellulose |
Lipids | Fatty acids, Glycerol | Triglycerides, Phospholipids, Steroids | Oils, Fats, Waxes, Cholesterol |
Proteins | Amino acids | Polypeptides | Keratin, Silk |
Nucleic Acids | Nucleotides | DNA, RNA | DNA, RNA |
Carbohydrates
Structure and Function
Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically in the ratio CH2O. They serve as fuel and building material for cells.
Monomers: Monosaccharides (simple sugars), e.g., glucose.
Disaccharides: Two monosaccharides joined by a glycosidic linkage (covalent bond formed by dehydration synthesis).
Polysaccharides: Polymers of many monosaccharides, used for energy storage and structural support.
Monosaccharides
General formula: (CH2O)n
Each carbon (except one) has a hydroxyl group; one carbon has a carbonyl group.
In aqueous solutions, monosaccharides with five or more carbons form ring structures.
Glucose is the most common monosaccharide and a primary energy source for cells.
Produced by photosynthetic organisms from CO2, H2O, and light.
Disaccharides
Disaccharides are formed by joining two monosaccharides via a glycosidic linkage.
Disaccharide | Monomers | Common Use |
|---|---|---|
Maltose | Glucose + Glucose | Important in beer brewing |
Lactose | Glucose + Galactose | Sugar present in milk |
Sucrose | Glucose + Fructose | Table sugar; most common disaccharide |
Polysaccharides
Polysaccharides are large macromolecules composed of hundreds or thousands of monosaccharides.
Formed by enzyme-mediated condensation reactions.
Serve two main biological functions:
Energy storage: Starch (plants), Glycogen (animals)
Structural support: Cellulose (plants), Chitin (fungi and arthropods)
Starch: Glucose polymer used for energy storage in plants.
Glycogen: Glucose polymer used for energy storage in animals, stored in muscle and liver cells.
Stored polysaccharides can be hydrolyzed to release glucose as needed.
Example: When energy is required, glycogen in animal liver cells is broken down via hydrolysis to release glucose into the bloodstream.
