Biomolecules Part 1 Recap: Carbohydrates and Related Reactions

Biomolecules Part 1 Recap

Learning Objectives

• Distinguish between dehydration reactions and hydrolysis reactions.

• Compare the structure and function of the three classes of carbohydrates: monosaccharides, disaccharides, and polysaccharides.

• Categorize common sugars into their respective classes.

• Compare the structure and function of major lipid types: triglycerides, phospholipids, and steroids.

Dehydration Synthesis and Hydrolysis

Overview

Dehydration synthesis and hydrolysis are fundamental chemical reactions involved in the formation and breakdown of biological macromolecules. These reactions are essential for the metabolism of carbohydrates, proteins, and nucleic acids.

• Dehydration Synthesis: A reaction in which two monomers are joined together by removing a molecule of water, forming a covalent bond. This process builds larger molecules from smaller units.

• Hydrolysis: A reaction in which a molecule is split into two smaller units by the addition of water, breaking a covalent bond. This process breaks down polymers into monomers.

• Example: Formation of sucrose from glucose and fructose via dehydration synthesis; breakdown of sucrose into glucose and fructose via hydrolysis.

Equation for Dehydration Synthesis:

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

Equation for Hydrolysis:

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

Carbohydrates

Definition and General Properties

Carbohydrates are organic molecules that include sugars and starches. They are composed of carbon (C), hydrogen (H), and oxygen (O), typically with a hydrogen to oxygen ratio of 2:1. Carbohydrates serve as a primary energy source and structural component in cells.

• Monosaccharides: Single sugar units; the monomers of carbohydrates. Examples include glucose, fructose, galactose, ribose, and deoxyribose.

• Disaccharides: Composed of two monosaccharide units joined by a glycosidic bond. Examples include sucrose, maltose, and lactose.

• Polysaccharides: Long chains of monosaccharide units; serve as energy storage or structural molecules. Examples include starch, glycogen, and cellulose.

Monosaccharides

Monosaccharides are the simplest carbohydrates and serve as building blocks for more complex sugars.

• Hexose sugars: Six-carbon sugars such as glucose, fructose, and galactose. These are isomers, meaning they have the same molecular formula but different structures.

• Pentose sugars: Five-carbon sugars such as ribose and deoxyribose, important in nucleic acids.

• General formula: $C_n(H_2O)_n$ (where n = 3–7)

Disaccharides

Disaccharides are formed by the dehydration synthesis of two monosaccharides.

• Sucrose: Glucose + Fructose

• Maltose: Glucose + Glucose

• Lactose: Galactose + Glucose

• Disaccharides are broken down into monosaccharides by hydrolysis.

Polysaccharides

Polysaccharides are large, complex carbohydrates composed of many monosaccharide units.

• Starch: Storage form of glucose in plants.

• Glycogen: Storage form of glucose in animals.

• Cellulose: Structural component in plant cell walls; not digestible by humans.

Classification Table: Common Carbohydrates

Type	Examples	Function
Monosaccharides	Glucose, Fructose, Galactose, Ribose, Deoxyribose	Energy source, building blocks for nucleic acids
Disaccharides	Sucrose, Maltose, Lactose	Transport form of sugars, energy source
Polysaccharides	Starch, Glycogen, Cellulose	Energy storage, structural support

Examples and Applications

• Glucose: Main energy source for cells.

• Ribose and Deoxyribose: Components of RNA and DNA, respectively.

• Cellulose: Provides structural support in plants; dietary fiber in human nutrition.

Additional info: The notes also mention lipids, but detailed content on lipids is not included in the provided images. Lipids, such as triglycerides, phospholipids, and steroids, are another major class of biomolecules important for cell structure and function.