1.3 Introduction to Macromolecules
Keywords
| English Term | 中文翻译 | Definition & Explanation |
|---|---|---|
| Monomer | 单体 | A small, basic molecular unit that can serve as a building block for a larger molecule. |
| Polymer | 聚合物/多聚体 | A large molecule consisting of many identical or similar monomers linked together by covalent bonds. |
| Dehydration Synthesis | 脱水缩合 | A chemical reaction in which two molecules covalently bond to each other with the removal of a water molecule. Also called a condensation reaction. |
| Hydrolysis | 水解 | A chemical reaction that breaks bonds between two molecules by the addition of water; functions in disassembly of polymers to monomers. |
| Covalent Bond | 共价键 | A strong chemical bond formed when two atoms share one or more pairs of valence electrons. |
1. The Building Blocks: Monomers and Polymers
Biological macromolecules are huge molecules (like proteins, nucleic acids, and carbohydrates) that are vital for life. Most of these macromolecules are polymers.
Analogy: Lego Bricks
Think of a monomer as a single Lego brick. By itself, it is just one small unit. But if you connect many of these individual bricks together using strong connections (covalent bonds), you can build a massive, complex structure like a castle or a spaceship. That large structure is the polymer.
Cells make and break down these polymers using two highly specific, enzyme-catalyzed chemical reactions: Dehydration Synthesis and Hydrolysis.
2. Building Macromolecules: Dehydration Synthesis
Dehydration synthesis occurs when two smaller molecules (monomers) are joined together to form a larger one. As the name suggests: * Dehydration: Losing water. * Synthesis: Building something.
How it works: To form a strong covalent bond between two unlinked monomers, one monomer provides a hydroxyl group (\(-OH\)), and the other provides a hydrogen ion (\(-H\)). These two combine and are removed from the molecules as a molecule of water (\(H_2O\)). The loss of the equivalent of a water molecule from the reactants allows the two remaining monomers to connect.
The process of connecting many monomers together in this way is known as polymerization.
- Biological Example: Your cells use dehydration synthesis to link individual amino acids (monomers) together to build a long polypeptide chain (a protein polymer).
3. Breaking Down Macromolecules: Hydrolysis
Hydrolysis is the exact reverse of dehydration synthesis. It is a chemical reaction involving the cleaving (breaking) of covalent bonds to break down large polymers into smaller monomers. * Hydro: Water. * Lysis: To break or cleave.
How it works: When water is added to the bond between monomers in a polymer, the covalent bond is broken. The water molecule (\(H_2O\)) splits: the hydrogen ion (\(-H\)) is attached to one monomer, and the hydroxyl group (\(-OH\)) is attached to the other monomer, completing the reaction and separating the pieces.
- Biological Example: Digestion. When you eat a piece of bread (starch, a huge polymer of glucose), enzymes in your digestive tract use hydrolysis to break it down into individual glucose monomers so your cells can absorb them.
Quiz
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