Biomolecules: Structure, Function, and Cellular Roles

Biomolecules: Structure and Importance

Introduction to Biomolecules

Biomolecules are organic molecules formed by living organisms and are essential for life. They are primarily composed of carbon, which is uniquely suited for building complex structures due to its four electrons in the valence shell.

• Organic molecules contain carbon and are found in all living things.

• Carbon's four valence electrons allow it to form stable covalent bonds with many elements, enabling the construction of large, complex molecules.

Formation of Macromolecules Within Cells

Major Elements and Macromolecule Synthesis

Cells use a limited set of elements—hydrogen, oxygen, nitrogen, carbon, phosphorus, and sulfur—to build macromolecules. These macromolecules include proteins, polysaccharides, and lipids, each assembled from smaller subunits.

• Amino acids are the building blocks of proteins.

• Simple sugars (e.g., glucose) are the monomers of polysaccharides.

• Acetyl CoA is a precursor for lipid synthesis, including fatty acids and cholesterol.

Common Functional Groups in Biomolecules

Functional Groups: Structure and Properties

Functional groups are specific groupings of atoms within molecules that confer characteristic chemical properties. They play a crucial role in the structure and function of biomolecules.

Chemical formula	Structure	Chemical property
–OH	O–H	Polar
–SH	S–H	Polar
–HPO4−	O P O	Polar
–COOH	O C OH	Acid
–NH2	N H H	Base

Additional info: Functional groups determine the solubility, reactivity, and interactions of biomolecules.

Carbohydrates

Structure and Function

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

• Monosaccharides are the simplest carbohydrates (e.g., glucose, galactose).

• Glucose is known as blood sugar and is a primary energy source.

• Polysaccharides (e.g., glycogen) are polymers made by linking monosaccharides.

Example: Glycogen is a branched polysaccharide formed by adding glucose units together.

Lipids

Hydrophobic and Amphipathic Properties

Lipids are a diverse group of hydrophobic molecules that do not dissolve in water. Some lipids, such as phospholipids, have both hydrophobic and hydrophilic regions, making them amphipathic.

• Hydrophobic molecules do not mix with water (e.g., fats, oils).

• Amphipathic molecules have both a polar (hydrophilic) end and a nonpolar (hydrophobic) end.

Additional info: Amphipathic lipids are essential for forming biological membranes.

Triglycerides ("Fats")

Triglycerides are the main form of stored energy in animals. They consist of a glycerol backbone attached to three fatty acid chains.

• Structure: 1 glycerol + 3 fatty acids

• Function: Long-term energy storage, insulation, and protection

Phospholipids

Phospholipids are a major component of cell membranes. They contain a phosphate group, a glycerol backbone, and two fatty acid tails.

• Hydrophilic head: Contains the phosphate group (–HPO4−)

• Hydrophobic tails: Two fatty acid chains

• Amphipathic nature: Allows phospholipids to form bilayers in aqueous environments, creating the structural basis of cell membranes.

Example: Phosphatidylcholine is a common phospholipid in animal cell membranes.