General Biology Study Guide: Biomolecules (Carbohydrates, Lipids, Proteins, Nucleic Acids)

Introduction to Biomolecules

Main Classes of Biomolecules

Biomolecules are essential organic compounds found in living organisms. They are classified into four major groups, each with distinct structures and functions.

• Carbohydrates: Serve as energy sources and structural components.

• Lipids: Function in energy storage, membrane structure, and signaling.

• Proteins: Perform a wide range of functions including catalysis, transport, and structural support.

• Nucleic Acids: Store and transmit genetic information.

Macromolecules are large molecules formed by polymerization of smaller subunits called monomers. Not all biomolecules are macromolecules (e.g., some lipids).

Carbohydrates

Monomers and Polymers

Carbohydrates are composed of monomers called monosaccharides (simple sugars). Polymers of carbohydrates include disaccharides (two monosaccharides) and polysaccharides (many monosaccharides).

• Monosaccharides: Glucose, fructose, galactose

• Disaccharides: Sucrose (glucose + fructose), maltose (glucose + glucose), lactose (glucose + galactose)

• Polysaccharides: Starch, glycogen, cellulose

Key Reactions: Dehydration and Hydrolysis

Two fundamental chemical reactions are involved in carbohydrate metabolism:

• Dehydration (Condensation) Reaction: Joins two monomers by removing a water molecule, forming a covalent bond.

• Hydrolysis Reaction: Breaks a covalent bond by adding water, splitting polymers into monomers.

Example equation:

$\text{Monomer}_1 + \text{Monomer}_2 \xrightarrow{\text{Dehydration}} \text{Dimer} + H_2O$

$\text{Dimer} + H_2O \xrightarrow{\text{Hydrolysis}} \text{Monomer}_1 + \text{Monomer}_2$

Classification and Structure

• Monosaccharides: Simple sugars with general formula $C_nH_{2n}O_n$ (e.g., glucose: $C_6H_{12}O_6$).

• Disaccharides: Formed by glycosidic bonds between two monosaccharides.

• Polysaccharides: Long chains of monosaccharides; can be linear (cellulose) or branched (glycogen, starch).

Glycosidic bond: Covalent bond formed between two monosaccharides via dehydration.

Examples and Applications

• Starch: Storage polysaccharide in plants; composed of amylose (linear) and amylopectin (branched).

• Glycogen: Storage polysaccharide in animals; highly branched.

• Cellulose: Structural polysaccharide in plant cell walls; linear and unbranched.

Table: Comparison of Major Polysaccharides

Polysaccharide	Structure	Function	Branching
Starch	Glucose polymer (amylose & amylopectin)	Energy storage (plants)	Branched & unbranched
Glycogen	Glucose polymer	Energy storage (animals)	Highly branched
Cellulose	Glucose polymer	Structural (plants)	Unbranched

Lipids

Types and Functions

Lipids are hydrophobic molecules that include fats, oils, phospholipids, and steroids. They are not true polymers.

• Fats (Triglycerides): Composed of glycerol and three fatty acids; used for energy storage.

• Phospholipids: Major component of cell membranes; contain glycerol, two fatty acids, and a phosphate group.

• Steroids: Four fused carbon rings; include cholesterol and hormones.

Saturated vs. Unsaturated Fatty Acids

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

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

Example: Olive oil contains unsaturated fatty acids; butter contains saturated fatty acids.

Phospholipids and Membranes

• Phospholipid bilayer: Hydrophilic (polar) heads face outward; hydrophobic (nonpolar) tails face inward.

Table: Structure of Major Lipids

Lipid Type	Components	Function
Triglyceride	Glycerol + 3 fatty acids	Energy storage
Phospholipid	Glycerol + 2 fatty acids + phosphate	Membrane structure
Steroid	Four fused rings	Hormones, membrane fluidity

Proteins

Structure and Levels of Organization

Proteins are polymers of amino acids, joined by peptide bonds. They have four levels of structure:

• Primary structure: Sequence of amino acids.

• Secondary structure: Local folding (alpha helix, beta sheet) stabilized by hydrogen bonds.

• Tertiary structure: Overall 3D shape due to interactions among R groups.

• Quaternary structure: Association of multiple polypeptide chains.

General formula for an amino acid:

$\text{NH}_2-\text{CHR}-\text{COOH}$

Where R is the side chain that determines the properties of each amino acid.

Peptide Bonds and Protein Function

• Peptide bond: Covalent bond between amino group of one amino acid and carboxyl group of another, formed by dehydration.

• Enzymes: Proteins that catalyze biochemical reactions.

• Denaturation: Loss of protein structure due to heat, pH, or chemicals.

Nucleic Acids

Structure and Components

Nucleic acids (DNA and RNA) are polymers of nucleotides. Each nucleotide consists of:

• Pentose sugar (deoxyribose in DNA, ribose in RNA)

• Phosphate group

• Nitrogenous base (adenine, guanine, cytosine, thymine in DNA; uracil replaces thymine in RNA)

Phosphodiester bond: Covalent bond joining nucleotides in a polynucleotide chain, formed by dehydration.

DNA vs. RNA

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Bases	A, T, G, C	A, U, G, C
Strands	Double	Single
Function	Genetic information storage	Protein synthesis, gene regulation

Base Pairing and Genetic Information

• Complementary base pairing: A-T (DNA), A-U (RNA), G-C

• Antiparallel strands: DNA strands run in opposite directions (5' to 3' and 3' to 5')

• Gene expression: Process by which information from DNA is used to synthesize proteins

Example equation:

$\text{DNA}: 5'\text{-ATGC-}3' \text{ pairs with } 3'\text{-TACG-}5'$

Summary Table: Nucleic Acid Components

Component	DNA	RNA
Sugar	Deoxyribose	Ribose
Base	A, T, G, C	A, U, G, C
Strands	Double	Single

Additional info:

• Some context and explanations have been inferred from standard biology curriculum to clarify fragmented or abbreviated points in the original material.

• Tables have been reconstructed to summarize key comparisons and classifications.