General Biology: Biomolecules and Their Functions

3.1 Carbon Atoms and Diversity in Organic Molecules

Carbon's Bonding Properties

Carbon atoms are the foundation of organic molecules due to their ability to form four covalent bonds, allowing for a vast diversity of molecular structures.

• Electron Configuration: Carbon's electron configuration (1s2 2s2 2p2) enables it to form stable covalent bonds with many elements.

• Diversity: This bonding capacity allows carbon to create large, complex molecules such as carbohydrates, proteins, lipids, and nucleic acids.

Hydrocarbons and Hydrophobicity

Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen. Their nonpolar nature makes them hydrophobic.

• Structure: Hydrocarbons can be chains or rings.

• Hydrophobicity: Lack of polar bonds means they do not mix well with water.

• Example: Fatty acids contain long hydrocarbon chains.

Organic Molecule Behavior and Functional Groups

The chemical behavior of organic molecules is determined by the presence and type of functional groups attached to the carbon skeleton.

• Functional Groups: Examples include hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), and phosphate (-PO4).

• Reactivity: Functional groups influence solubility, reactivity, and interactions with other molecules.

ATP Structure and Energy

ATP (adenosine triphosphate) is the primary energy carrier in cells. Its structure allows for the storage and release of energy.

• High-Energy Bonds: The phosphate bonds in ATP are unstable and release energy when broken.

• Equation: $\text{ATP} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

3.2 Macromolecules: Polymers and Monomers

Polymers vs. Monomers

Macromolecules are large molecules formed by joining smaller units called monomers.

• Monomers: Simple molecules that can join together (e.g., glucose, amino acids, nucleotides).

• Polymers: Chains of monomers (e.g., starch, proteins, DNA).

• Polymerization: The process of linking monomers to form polymers.

Dehydration and Hydrolysis Reactions

Polymer formation and breakdown involve dehydration and hydrolysis reactions.

• Dehydration: Removal of water to join monomers.

• Hydrolysis: Addition of water to break polymers into monomers.

• Example: Formation of maltose from two glucose molecules via dehydration.

3.3 Carbohydrates: Structure and Function

Monosaccharides, Disaccharides, and Polysaccharides

Carbohydrates are essential for energy storage and structural support in cells.

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides joined (e.g., sucrose, lactose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose, glycogen).

Functions of Polysaccharides

• Storage: Starch (plants) and glycogen (animals) store energy.

• Structure: Cellulose (plants) provides structural support; chitin (fungi and arthropods) forms exoskeletons.

3.4 Lipids: Hydrophobic Molecules

Types and Functions of Lipids

Lipids are a diverse group of hydrophobic molecules, including fats, phospholipids, and steroids.

• Fats: Composed of glycerol and fatty acids; store energy.

• Phospholipids: Major component of cell membranes.

• Steroids: Include hormones like cholesterol.

Saturated vs. Unsaturated Fats

• Saturated Fats: No double bonds; solid at room temperature.

• Unsaturated Fats: One or more double bonds; liquid at room temperature.

3.5 Proteins: Structure and Function

Amino Acids and Protein Formation

Proteins are polymers of amino acids, each with a unique side chain (R group) that determines its properties.

• Peptide Bonds: Link amino acids via dehydration reactions.

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Alpha helices and beta sheets formed by hydrogen bonding.

• Tertiary Structure: 3D folding due to interactions among side chains.

• Quaternary Structure: Multiple polypeptide chains forming a functional protein.

Protein Denaturation

• Denaturation: Loss of protein structure due to changes in temperature, pH, or chemicals.

• Effect: Denatured proteins lose their biological function.

3.6 Nucleic Acids: Information Storage and Transmission

Nucleotides and Nucleic Acid Structure

Nucleic acids (DNA and RNA) store and transmit hereditary information. They are polymers of nucleotides.

• Nucleotide Structure: Each nucleotide consists of a nitrogenous base, a pentose sugar, and a phosphate group.

• Types of Nitrogenous Bases:

  • Purines: Adenine (A), Guanine (G)

  • Pyrimidines: Cytosine (C), Thymine (T), Uracil (U)

• Nucleoside: Nitrogenous base + sugar (no phosphate)

• Nucleotide: Nitrogenous base + sugar + phosphate

• Directionality: Nucleic acids have a 5' end and a 3' end, indicating the orientation of the sugar-phosphate backbone.

Formation of Nucleic Acids

• Polymerization: Nucleotides are joined by phosphodiester bonds between the 3' hydroxyl group of one sugar and the 5' phosphate of the next.

• Equation: $\text{Nucleotide}_n + \text{Nucleotide}_m \rightarrow \text{Nucleic Acid} + (n+m-1)\text{H}_2\text{O}$

Table: Comparison of Biomolecule Types

Biomolecule	Monomer	Polymer	Main Function
Carbohydrate	Monosaccharide	Polysaccharide	Energy storage, structure
Lipid	Fatty acid, glycerol	Triglyceride, phospholipid	Energy storage, membranes
Protein	Amino acid	Polypeptide	Catalysis, structure, transport
Nucleic Acid	Nucleotide	DNA, RNA	Information storage, transmission