Macromolecules I: Structure, Synthesis, and Function

Macromolecules: An Introduction

Macromolecules are large, complex molecules essential for life, composed of smaller subunits. They play critical roles in structure, function, and regulation of the body's tissues and organs.

• Four Major Classes: Carbohydrates, Lipids, Proteins, and Nucleic Acids

• All macromolecules contain carbon, hydrogen, and oxygen; some also contain nitrogen and other elements.

• Foods such as bread, grains, fruits, and cheese are rich sources of macromolecules.

Monomers vs Polymers

Macromolecules are often polymers, which are long chains of repeating subunits called monomers, linked by covalent bonds.

• Monomers: Small, basic molecular units (e.g., glucose, amino acids, nucleotides).

• Polymers: Large molecules formed by joining many monomers together (e.g., starch, proteins, DNA).

• Monomers are linked via covalent bonds to form polymers.

Polymer Synthesis and Hydrolysis

Dehydration Synthesis (Condensation Reaction)

Dehydration synthesis is the process by which two monomers are joined, resulting in the loss of a water molecule and the formation of a covalent bond.

• Example: Two glucose molecules combine to form maltose (a disaccharide) and water.

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

Hydrolysis Reaction

Hydrolysis is the reverse of dehydration synthesis. It breaks polymers into monomers by adding water, splitting the covalent bond.

• One monomer receives a hydrogen ion (H+), the other receives a hydroxyl group (OH-).

• Example: Maltose is broken down into two glucose molecules by hydrolysis.

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

Enzymes and Catalysis of Macromolecule Reactions

Reactions involving macromolecules are catalyzed by enzymes, which are biological molecules that speed up chemical reactions.

• Enzymes lower the activation energy required for hydrolysis and dehydration reactions.

• Dehydration reactions form new bonds and require energy.

• Hydrolysis reactions break bonds and release energy.

• Specific enzymes exist for each macromolecule class:

  • Carbohydrates: Broken down by amylase, sucrase, lactase

  • Lipids: Broken down by lipases

  • Proteins: Broken down by pepsin and peptidase

Carbohydrates

Carbohydrates are organic molecules found in grains, fruits, and vegetables, serving as a primary energy source for the body.

• General formula: $C_n(H_2O)_n$

• Ratio of elements: Carbon:Hydrogen:Oxygen = 1:2:1

• Provide energy to the body in the form of glucose.

Types of Carbohydrates

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

• Disaccharides: Two monosaccharides joined by a glycosidic bond (e.g., sucrose, lactose, maltose)

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

Monosaccharides: Structure and Isomerism

Monosaccharides are classified by the number of carbon atoms and the position of their carbonyl group.

• Common forms: Trioses (3C), Pentoses (5C), Hexoses (6C)

• Can exist as linear chains or ring structures in aqueous solutions.

• Isomers: Glucose, galactose, and fructose are structural isomers (same formula, different structure).

Disaccharides: Formation and Examples

Disaccharides are formed by joining two monosaccharides via a glycosidic linkage, releasing water.

• Sucrose: Glucose + Fructose

• Lactose: Glucose + Galactose

• Maltose: Glucose + Glucose

• Glycosidic linkage: Covalent bond between the 1st carbon of one sugar and the 4th carbon of another (commonly 1-4 linkage).

Polysaccharides: Structure and Function

Polysaccharides are large polymers of monosaccharides, serving structural and storage roles.

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

• Glycogen: Storage form in animals; highly branched.

• Cellulose: Structural component in plant cell walls; linear chains joined by β 1-4 glycosidic bonds.

Polysaccharide	Monomer	Function	Branching
Starch	Glucose	Energy storage in plants	Amylose (unbranched), Amylopectin (branched)
Glycogen	Glucose	Energy storage in animals	Highly branched
Cellulose	Glucose	Structural (plant cell wall)	Unbranched, linear

Additional info: The notes also reference lipids, proteins, and nucleic acids, but the detailed content in the provided slides focuses on carbohydrates and general macromolecule structure and synthesis. For a complete study guide, further sections on lipids, proteins, and nucleic acids would be included in subsequent lectures.