Functional Groups and Biological Macromolecules: Structure and Formation

Functional Groups in Biological Molecules

Introduction

Functional groups are specific groups of atoms within molecules that determine the chemical properties and reactivity of those molecules. Understanding these groups is essential for studying the structure and function of biological macromolecules.

Hydroxyl Group

• Composition: Made of oxygen (O) and hydrogen (H).

• Polarity: Polar group.

• Interactions: Can interact with water and form hydrogen bonds.

• Example: The hydroxyl group is found in alcohols such as ethanol.

Carboxyl Group

• Composition: Made of carbon (C), two oxygens (O), and a hydrogen (H).

• Polarity: Polar group.

• Interactions: Interacts with water.

• Acidic Properties: Acts as an acid by donating an H+ ion.

• Additional info: Also contains a hydroxyl group within its structure.

• Example: Found in amino acids and fatty acids.

Amino Group

• Composition: Made of nitrogen (N) and hydrogen (H).

• Polarity: Polar group.

• Interactions: Interacts with water.

• Basic Properties: Acts as a base by accepting an H+ ion.

• Example: Found in amino acids.

Phosphate Group

• Composition: Includes phosphorus (P) and oxygen (O).

• Polarity: Nonpolar overall, but negatively charged.

• Interactions: Interacts with water due to its charge.

• Reactivity: Highly reactive.

• Example: Found in nucleic acids (DNA, RNA) and ATP.

Biological Macromolecules

Introduction

Smaller molecules, called monomers, are chemically linked together to form larger biological macromolecules, or polymers. These macromolecules are essential for life and include carbohydrates, lipids, proteins, and nucleic acids.

• Carbohydrates

• Lipids

• Proteins

• Nucleic Acids

Polymer Formation and Breakdown

How Are Larger Molecules Formed?

Polymers are formed from monomers through dehydration reactions, which involve the removal of water.

• Dehydration Reaction: A short polymer and an unlinked monomer join together.

• The hydroxyl group at the end of the polymer bonds with a hydrogen atom at the end of the unlinked monomer.

• This forms water ($H_2O$), which is released during the reaction.

• The short polymer and the unlinked monomer then join together to form a longer polymer.

• Analogy: Two people from different families (H and OH) get married and move out together into a new home; their respective families (the in-laws) join together and move into a bigger house.

How Are Larger Molecules Broken Down?

Polymers are broken down into monomers through hydrolysis reactions, which involve the addition of water.

• Hydrolysis Reaction: To "break" (lysis) a polymer, a water molecule is added.

• This breaks a bond between two monomers in the polymer.

• Analogy: A married couple gets divorced and moves back to their respective families; the big house gets sold and they go back to living their individual lives.

Note: Hydrolysis is the inverse of dehydration.

Summary Table: Functional Groups and Their Properties

Functional Group	Composition	Polarity	Key Properties	Example
Hydroxyl	O, H	Polar	Hydrogen bonding, interacts with water	Alcohols (e.g., ethanol)
Carboxyl	C, O, H	Polar	Acidic, donates H+, interacts with water	Amino acids, fatty acids
Amino	N, H	Polar	Basic, accepts H+, interacts with water	Amino acids
Phosphate	P, O	Nonpolar (negatively charged)	Highly reactive, interacts with water	Nucleic acids, ATP