There are four types of very large molecules that are important to life. These are carbohydrates, nucleic acids, lipids, and proteins. Although these are quite diverse in terms of structure, size, and function, the same mechanisms build and break them down:
• All are comprised of single units linked together to create a chain, similar to a freight train with many cars.
• All the monomers or single units contain carbon.
• All monomers are linked together through a process known as dehydration synthesis, which literally means "building by removing water." A hydrogen atom (H) is removed from one monomer, and a hydroxide (OH) group is removed from the next monomer in line. Atoms on the ends of the two monomers will then form a covalent bond to fill their electron shells, thereby building a polymer.
• All polymers are broken down by the same method, hydrolysis.
Hydrolysis means "breaking with water." By adding H2O, which
contains hydrogen and hydroxide groups, back to the monomers, the bond is
broken and the macromolecule separates into smaller pieces.
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