Condensation Reactions
Definition
Condensation
Condensation is a reaction where two molecules combine, releasing water.
- It is enzyme-catalyzed, requires energy input, and typically occurs inside cells.
- The removal of H₂O allows the formation of a covalent bond between the reacting functional groups.
- These reactions are reversible via hydrolysis, which breaks the polymer back into monomers by adding water.
- Think of condensation reactions as building a brick wall (polymer) from individual bricks (monomers).
- The mortar that holds them together is formed by removing water from the bricks!
Key Macromolecules Formed by Condensation
- The main types of biological macromolecules produced through condensation are:
- Polysaccharides
- Polypeptides (proteins)
- Nucleic acids (DNA and RNA)
- Each type of macromolecule has distinct monomers, bond types, and biological functions.
1. Polysaccharides (Carbohydrates)
- Monomer
- Monosaccharides single sugar units with the general formula (CH₂O)n.
- Examples: α-glucose, β-glucose, galactose, fructose
- Reaction
- Glycosidic bond formation occurs between hydroxyl (-OH) groups on two monosaccharides.
- Enzyme example: maltase catalyzes maltose formation
- By-product: one molecule of H₂O per glycosidic bond
| Polysaccharide | Monomer | Bondy Type | Function | Structure |
|---|---|---|---|---|
| Starch | α-glucose | α(1→4) and α(1→6) | Energy storage in plants | Amylose (unbranched), Amylopectin (branched) |
| Glycogen | α-glucose | α(1→4), α(1→6) | Energy storage in animals (liver, muscle) | Highly branched |
| Cellulose | β-glucose | β(1→4) | Structural component in plant cell walls | Straight chains; form microfibrils |
2. Polypeptides (Proteins)
- Monomer:
- Amino acids contain a central carbon (C) bonded to:
- An amino group (-NH₂)
- A carboxyl group (-COOH)
- A hydrogen atom
- A variable R group (determines identity)
- Reaction:
- Peptide bond forms between the amino group of one amino acid and the carboxyl group of another.
- The reaction removes H₂O (from -OH of carboxyl and H of amino group).
- Enzyme-catalyzed during translation (ribosome-mediated)
Definition
Peptide bond
A peptide bond is a covalent bond formed between the carboxyl group of one amino acid and the amino group of another.
- Dipeptide: two amino acids joined by one peptide bond.
- Polypeptide: chain of many amino acids.
- Protein: one or more polypeptides folded into a specific 3D structure (primary to quaternary levels).
| Protein | Function | Example |
|---|---|---|
| Enzymes | Catalyze metabolic reactions | e.g., amylase, pepsin |
| Hormones | Regulation of physiology | e.g., insulin |
| Structural | Support and integrity | e.g., collagen |
| Transport | Movement of molecules | e.g., hemoglobin (O₂ transport) |
| Antibodies | Immune defense | Specific binding to antigens |
The sequence of amino acids determines protein folding, which determines function.
3. Nucleic Acids (DNA and RNA)
- Monomer:
- Nucleotides, each composed of:
- Phosphate group
- Pentose sugar (deoxyribose in DNA, ribose in RNA)
- Nitrogenous base (A, T/U, G, C)
- Reaction:
- Phosphodiester bond forms between the phosphate group of one nucleotide and the 3′-OH group of the sugar on another nucleotide.
- Water is released during each bond formation.
- Forms the sugar-phosphate backbone of DNA/RNA.
Definition
Phosphodiester bond
A phosphodiester bond is a covalent bond formed between nucleotides in a nucleic acid chain via condensation.
- Polymer:
- DNA: double-stranded helix; stores genetic instructions
- RNA: single-stranded, involved in protein synthesis (mRNA, tRNA, rRNA)
Always mention water release and the specific bond type (e.g., glycosidic, peptide, or phosphodiester) in your answers to get full marks!
NoteDNA strands are antiparallel and held together by hydrogen bonds between complementary bases
Self review- Explain how a glycosidic bond is formed between two glucose molecules.
- Describe the formation of a dipeptide from two amino acids, including the functional groups involved.
- Outline the role of condensation reactions in the synthesis of DNA.
- Explain why water is released during the formation of a phosphodiester bond in a nucleotide chain.
