Overview of Biomolecules: Carbohydrates and Related Concepts

Biomolecules

Carbohydrates

Carbohydrates are essential biomolecules that serve as a primary source of energy and structural components in living organisms. They are composed of carbon, hydrogen, and oxygen, typically with a hydrogen:oxygen ratio of 2:1, similar to water.

• Definition: Carbohydrates are organic molecules consisting of monosaccharide units (simple sugars) or their polymers.

• General Formula: Most carbohydrates have the empirical formula $(CH_2O)_n$ where n is the number of carbon atoms.

• Classification:

  • Monosaccharides: Simple sugars such as glucose and fructose.

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

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

• Functions:

  • Energy storage (e.g., starch in plants, glycogen in animals).

  • Structural support (e.g., cellulose in plant cell walls).

  • Recognition and signaling (e.g., glycoproteins on cell surfaces).

• Examples: Glucose (C_6H_{12}O_6), a key energy source in cellular respiration.

Additional info: The notes mention 'reserve' and 'structural' roles, which correspond to storage (e.g., starch, glycogen) and structural (e.g., cellulose, chitin) polysaccharides.

Polysaccharides: Storage and Structural Roles

Polysaccharides are large carbohydrate molecules formed by the polymerization of monosaccharides. Their function depends on their structure and the type of monomers involved.

• Storage Polysaccharides:

  • Starch: The main storage carbohydrate in plants, composed of amylose and amylopectin.

  • Glycogen: The primary storage carbohydrate in animals, highly branched for rapid energy release.

• Structural Polysaccharides:

  • Cellulose: A major component of plant cell walls, providing rigidity and strength.

  • Chitin: Found in the exoskeleton of arthropods and fungal cell walls.

Example: Cellulose is indigestible to humans but can be broken down by certain bacteria and fungi.

Monosaccharides and Disaccharides

Monosaccharides are the simplest form of carbohydrates, while disaccharides are formed by the condensation of two monosaccharides.

• Monosaccharides: Glucose, fructose, galactose.

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

• Glycosidic Bond: The covalent bond formed between two monosaccharides during dehydration synthesis.

Equation for Dehydration Synthesis:

$\text{Monosaccharide}_1 + \text{Monosaccharide}_2 \rightarrow \text{Disaccharide} + H_2O$

Summary Table: Types of Carbohydrates

Type	Example	Function
Monosaccharide	Glucose	Immediate energy source
Disaccharide	Sucrose	Transported sugar in plants
Polysaccharide (Storage)	Starch, Glycogen	Energy storage
Polysaccharide (Structural)	Cellulose, Chitin	Structural support

Additional info: Table entries inferred and expanded for clarity.

Key Terms

• Monosaccharide: The simplest carbohydrate, a single sugar unit.

• Disaccharide: A carbohydrate composed of two monosaccharides.

• Polysaccharide: A complex carbohydrate made of many monosaccharide units.

• Glycosidic Bond: The covalent bond linking monosaccharides in disaccharides and polysaccharides.