General Biology: Structure and Function of Biological Macromolecules

Carbon and the Molecular Diversity of Life

Formation of Bonds with Carbon

Carbon is a versatile element that forms the backbone of most biological molecules due to its ability to form four covalent bonds with other atoms.

• Valence electrons: Carbon has four valence electrons, allowing it to bond with a variety of atoms.

• Bonding: Can form single, double, or triple covalent bonds, primarily with H, O, N, and other carbons.

• Complex molecules: Enables the formation of large, complex organic molecules.

Molecular Diversity from Carbon Skeleton Variation

Variation in carbon skeletons leads to molecular diversity in organic compounds.

• Carbon chains: Can be branched, linear, or form rings; may have single, double, or triple bonds.

• Hydrocarbons: Organic molecules composed only of carbon and hydrogen; hydrophobic and can release energy during reactions.

• Functional groups: Chemical groups attached to carbon skeletons that affect molecular function and participate in chemical reactions.

Table: Major Functional Groups Important to Life

Functional Group	Structure	Properties
Hydroxyl	-OH	Polar, forms hydrogen bonds
Carbonyl	C=O	Found in sugars
Carboxyl	-COOH	Acts as acid
Amino	-NH2	Acts as base
Sulfhydryl	-SH	Forms disulfide bonds
Phosphate	-PO4	Contributes negative charge
Methyl	-CH3	Affects gene expression

ATP: The Energy Currency of the Cell

Structure and Function of ATP

Adenosine triphosphate (ATP) is the primary energy source for cellular processes.

• Structure: ATP consists of adenosine attached to three phosphate groups.

• Function: Stores potential energy; releases energy when hydrolyzed.

• Role: Drives cellular work by providing energy for reactions.

Organic Compounds and Macromolecules

Types of Organic Compounds

Organic compounds contain carbon and hydrogen and serve as the foundation for biological macromolecules.

• Carbohydrates

• Lipids

• Proteins

• Nucleic acids

Macromolecules: Polymers Built from Monomers

Most biological macromolecules are polymers, except lipids.

• Polymer: Large molecule made of repeating monomer units linked by covalent bonds.

• Dehydration reaction: Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

Carbohydrates: Fuel and Building Material

Classification and Structure

Carbohydrates are classified by the number of carbon atoms and serve as energy sources and structural components.

• Monosaccharides: Simple sugars (e.g., glucose), major energy source for cells.

• Disaccharides: Two monosaccharides linked by glycosidic bonds (e.g., sucrose, lactose).

• Polysaccharides: Long chains of monosaccharides; function as energy storage (starch, glycogen) or structural components (cellulose).

Table: Types of Carbohydrates

Type	Example	Function
Monosaccharide	Glucose	Energy source
Disaccharide	Sucrose	Transport sugar in plants
Polysaccharide	Starch	Energy storage in plants
Polysaccharide	Cellulose	Structural support in plants

Lipids: Hydrophobic Molecules

Types and Functions of Lipids

Lipids are hydrophobic molecules that do not form true polymers and serve as energy storage, membrane structure, and signaling molecules.

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

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

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

• Phospholipids: Major component of cell membranes; amphipathic with hydrophilic heads and hydrophobic tails.

• Steroids: Lipids with four fused rings; cholesterol is a key membrane component and precursor for steroid hormones.

Table: Comparison of Saturated and Unsaturated Fatty Acids

Type	Bond Type	Physical State	Source
Saturated	Single bonds	Solid	Animal
Unsaturated	Double bonds	Liquid	Plant

Proteins: Diversity of Structure and Function

Structure of Proteins

Proteins are polymers of amino acids and perform a wide range of cellular functions.

• Amino acids: 20 types; each has a central carbon, amino group, carboxyl group, hydrogen atom, and variable R group.

• Polypeptide: Chain of amino acids linked by peptide bonds.

• Protein: One or more polypeptides folded into a specific 3D structure.

Levels of Protein Structure

• Primary structure: Linear sequence of amino acids; determined by genes.

• Secondary structure: Local folding (α-helix, β-pleated sheet) due to hydrogen bonding.

• Tertiary structure: Overall 3D shape; interactions among R groups (hydrogen bonds, hydrophobic interactions, disulfide bridges).

• Quaternary structure: Association of multiple polypeptides (e.g., hemoglobin).

Protein Function and Denaturation

• Functions: Enzymatic activity, transport, defense, storage, communication, movement, structural support.

• Denaturation: Loss of structure due to changes in temperature, pH, or salt concentration.

Table: Levels of Protein Structure

Level	Description	Example
Primary	Sequence of amino acids	Insulin
Secondary	α-helix, β-sheet	Keratin
Tertiary	3D folding	Albumin
Quaternary	Multiple polypeptides	Hemoglobin

Nucleic Acids: Storage and Transmission of Hereditary Information

Roles and Types of Nucleic Acids

Nucleic acids store and transmit genetic information. Two main types are DNA and RNA.

• DNA (Deoxyribonucleic acid): Stores genetic information; directs synthesis of messenger RNA (mRNA) and proteins.

• RNA (Ribonucleic acid): Involved in protein synthesis and gene expression.

Structure of Nucleic Acids

• Nucleotides: Monomers of nucleic acids; composed of a nitrogenous base, pentose sugar, and phosphate group.

• Phosphodiester linkage: Bonds nucleotides together, forming a sugar-phosphate backbone.

• Directionality: 5' end (phosphate group) and 3' end (hydroxyl group).

Table: Nitrogenous Bases in DNA and RNA

Base	DNA	RNA
Adenine (A)	Yes	Yes
Guanine (G)	Yes	Yes
Cytosine (C)	Yes	Yes
Thymine (T)	Yes	No
Uracil (U)	No	Yes

Structures of DNA and RNA Molecules

• DNA: Double helix; two antiparallel strands held together by complementary base pairing (A-T, G-C).

• RNA: Usually single-stranded; can form complementary base pairs (A-U, G-C).

Key Equations and Concepts

• Dehydration synthesis: $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + \text{H}_2\text{O}$

• Hydrolysis: $\text{Polymer} + \text{H}_2\text{O} \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

• ATP hydrolysis: $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{Energy}$

• Phosphodiester bond formation: $\text{Nucleotide}_1 + \text{Nucleotide}_2 \rightarrow \text{Dinucleotide} + \text{H}_2\text{O}$

Additional info: These notes expand on the original content by providing definitions, examples, and tables for clarity and completeness, suitable for college-level General Biology study.