4.1

• Carbon skeletons and functional groups are identified in organic molecules.
• Monomers and polymers are related.
• The processes of building and breaking polymers are described.
• Organic molecules are composed of a backbone of carbon atoms bonded to one another.
• Atoms of other elements may branch off this carbon backbone.
• The basic structure of organic molecules is the foundation of the wide range of life's molecules.
• Carbon can form bonds with one or more other carbon atoms, producing an endless variety of carbon skeletons.
• Most carbon-based molecules are classified as organic molecules.
• Non-carbon-based molecules such as water (H 2 O), oxygen (O 2 ), and ammonia (NH 3 ) are classified as inorganic molecules.
• The carbon backbones of organic molecules can take many shapes.
• These molecules may include single, double, and rarely, triple bonds.
• The only rule is that each carbon forms a total of four bonds.
• Carbon may also bond with atoms of other elements.
• Organic molecules that are composed of only carbon and hydrogen are known as hydrocarbons.
• Many hydrocarbons are important fuels.
• Methane (CH 4 ) is one of the most abundant hydrocarbons in natural gas, a fuel used to heat homes.
• In your body, energy-storing fat molecules contain long hydrocarbon chains.
• In addition to hydrogen, two other atoms frequently found in organic molecules are oxygen and nitrogen.
• Cells link monomers together into long chains called polymers.
• Life's large molecules are classified into four main categories: carbohydrates, lipids, proteins, and nucleic acids.
• Other polymers have branching chains or chains that fold back on themselves.
• Every living cell has thousands of different kinds of polymers.
• A group of atoms within a molecule that interacts in predictable ways with other molecules is called a functional group.
• Some biomolecules may be composed of hundreds or even millions of atoms.
• These large molecules are built from many similar, smaller molecular units called monomers.
• The diversity of life's polymers is vast.
• The specific molecules vary from cell to cell within an organism.
• Cells break bonds between monomers by adding water to them, the reverse of dehydration, a process called a hydrolysis reaction.
• Many of the molecules in your food are polymers, which must be broken down to make their monomers available to your cells.
• The variety of polymers differs among individuals of the same species, and even more among organisms of different species.
• Each time a monomer is added to a chain, a water molecule is released, a process called a dehydration reaction.
• The structure and role of nucleic acids, such as DNA, will be explored in depth in Chapter 11.
• A polymer may be a straight chain of monomers, much as a train is a string of many individual cars.
• All of these polymers are built from a collection of fewer than 50 kinds of monomers.
• In the next sections of this chapter, you'll explore the properties of carbohydrates, lipids, and proteins.
• Organisms not only build polymers; they also have to break them down.
• The carbon skeleton and the attached functional groups determine the properties of an organic molecule.
• Hydroxyl groups are hydrophilic, meaning they attract water molecules.
• Most organic molecules that contain hydroxyl groups are hydrophilic, which literally means "water-loving." These molecules tend to become surrounded by water molecules in an aqueous environment.
• These four common functional groups give specific properties to the organic molecules that contain them.