General Biology: Functional Groups, Carbohydrates, and Lipids

Atoms, Molecules, and Functional Groups

Functional Groups and Their Importance

Functional groups are specific groups of atoms within molecules that have distinct chemical properties. These groups confer particular characteristics to larger molecules, influencing their shape, reactivity, and interactions in biological systems.

• Definition: Small groups of atoms with specific chemical properties.

• Role: Determine molecular shape and reactivity.

• Example: The hydroxyl group (-OH) makes molecules more hydrophilic.

Common Functional Groups in Biology

Functional Group	Class of Compounds	Properties
Hydroxyl (-OH)	Alcohols	Polar; forms hydrogen bonds; increases solubility in water.
Aldehyde (-CHO)	Aldehydes	Reactive; important in energy-releasing reactions.
Keto (C=O)	Ketones	Polar; important in carbohydrates and energy reactions.
Carboxyl (-COOH)	Carboxylic acids	Acidic; ionizes to form COO- and H+; involved in peptide bonds.
Amino (-NH2)	Amines	Basic; accepts H+; involved in peptide bonds.
Phosphate (-PO42-)	Organic phosphates	Acidic; links nucleotides in nucleic acids; energy transfer.
Sulfhydryl (-SH)	Thiols	Forms disulfide bonds in proteins.
Methyl (-CH3)	Methylated compounds	Nonpolar; affects gene expression.

Macromolecules and Polymers

Types of Biological Macromolecules

Biological macromolecules are large molecules essential for life, including proteins, carbohydrates, nucleic acids, and lipids.

• Proteins: Polymers of 20 different amino acids.

• Carbohydrates: Polymers of sugar monomers (monosaccharides).

• Nucleic acids: Polymers of nucleotide monomers.

• Lipids: Non-polymeric, but held together by hydrophobic interactions.

Polymer Formation and Breakdown

• Condensation (Dehydration) Reaction: Monomers are joined by removing water, forming a covalent bond.

• Hydrolysis: Polymers are broken down into monomers by the addition of water.

Equations:

• Condensation: $\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + H_2O$

• Hydrolysis: $\text{Polymer} + H_2O \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

Carbohydrates

Overview and Functions

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They serve as energy sources, structural components, and recognition molecules in cells.

• Source of stored energy

• Transport of energy within organisms

• Structural roles (e.g., in cell walls)

• Cell recognition and signaling

Monosaccharides

Monosaccharides are the simplest carbohydrates, also known as simple sugars.

• Pentoses: 5-carbon sugars (e.g., ribose, deoxyribose in RNA and DNA)

• Hexoses: 6-carbon sugars (e.g., glucose, fructose, mannose, galactose)

Disaccharides and Glycosidic Linkages

Disaccharides are formed when two monosaccharides are covalently bonded via a glycosidic linkage, a type of condensation reaction.

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

Oligosaccharides

Oligosaccharides are short chains of monosaccharide units. They often have additional functional groups and are commonly attached to proteins and lipids, playing roles in cell recognition (e.g., blood group antigens).

Polysaccharides

Polysaccharides are large carbohydrate polymers. Their structure can be linear or branched, and they serve various functions depending on their composition and structure.

• Starch: Main storage polysaccharide in plants; polymer of glucose.

• Glycogen: Highly branched polymer of glucose; main storage polysaccharide in animals.

• Cellulose: Main component of plant cell walls; most abundant organic compound on Earth; provides structural support.

Comparison of Major Polysaccharides

Polysaccharide	Monomer	Structure	Function
Starch	Glucose	Branched or unbranched	Energy storage in plants
Glycogen	Glucose	Highly branched	Energy storage in animals
Cellulose	Glucose	Linear, unbranched	Structural support in plants

Lipids

Properties and Functions of Lipids

Lipids are hydrophobic molecules composed mainly of carbon and hydrogen. They are not true polymers but are essential for energy storage, membrane structure, and insulation.

• Insoluble in water due to nonpolar covalent bonds

• Held together by van der Waals interactions

• Store energy in C—C and C—H bonds

• Structural roles in cell membranes

• Thermal insulation in animals

Triglycerides (Fats and Oils)

Triglycerides are the main form of stored energy in animals and plants. They are composed of three fatty acids and one glycerol molecule, joined by condensation reactions.

• Fats: Solid at room temperature; mostly saturated fatty acids.

• Oils: Liquid at room temperature; mostly unsaturated fatty acids.

• Very hydrophobic due to nonpolar fatty acid chains.

Structure of Triglycerides

• Three fatty acids (long hydrocarbon chains with a carboxyl group at one end)

• One glycerol (a three-carbon alcohol with hydroxyl groups)

• Equation for triglyceride synthesis:

$\text{Glycerol} + 3\ \text{Fatty Acids} \rightarrow \text{Triglyceride} + 3\ H_2O$

Saturated vs. Unsaturated Fatty Acids

• Saturated fatty acids: All carbon-carbon bonds are single; chains are straight and pack tightly; solid at room temperature.

• Unsaturated fatty acids: One or more double bonds; chains are kinked and do not pack tightly; liquid at room temperature.

Example: Butter (saturated fat) is solid, while olive oil (unsaturated fat) is liquid at room temperature.

Summary Table: Saturated vs. Unsaturated Fatty Acids

Type	Bond Type	Structure	Physical State
Saturated	Single C–C bonds	Straight chains	Solid at room temp
Unsaturated	One or more C=C bonds	Kinked chains	Liquid at room temp