Lipids are a class of organic macromolecule. Lipids are characterized by their nonpolar (non-water-soluble) nature.
Most notably, lipids include triglycerides (fats), oils, steroids, waxes, and phospholipids.
What functional groups are present in a typical fatty acid?
A fatty acid includes a carboxylic acid (COOH) group attached to a hydrocarbon chain.
Fatty acids can combine with glycerol to form triglycerides, or fat. Fatty acids can also be broken down to provide cells with energy.
What type of lipid is pictured here?
The lipid pictured here is a triglyceride, commonly known simply as a fat.
A triglyceride consists of three fatty acid molecules attached to a three-carbon glycerol backbone.
The diagram below depicts a fatty acid. Is this fatty acid saturated, monounsaturated, or polyunsaturated?
This fatty acid is polyunsaturated.
Saturated fatty acids have carbon chains that include only single bonds, while unsaturated fatty acids include one or more double bonds in their chains. Since this fatty acid contains three carbon-carbon double bonds, it is polyunsaturated. (To be monounsaturated, a fatty acid must include only one double bond in its carbon chain.)
What type of lipid would be expected to be most predominant in a eukaryotic cell membrane?
The cell membrane (in both eukaryotes and prokaryotes) is composed mainly of phospholipids in the form of a "bilayer," or double layer.
What class of lipid is derived from the molecule below and plays a vital role in the endocrine system?
Steroid hormones are derived from cholesterol (shown here). These lipid molecules can be easily spotted due to their structures, which include four fused rings.
A typical phospholipid includes both a polar "head" region and two nonpolar "tails." What term describes this property of having both polar and nonpolar regions?
Molecules with both polar and nonpolar regions are amphipathic.
Specifically, the polar "head" region includes phosphate, which is charged; this charge is what gives the head group its polarity. The two "tails" consist of fatty acids, which are largely nonpolar due to their long hydrocarbon chains.
Nucleic acids are a class of organic macromolecule. These molecules consist of long chains of nucleotide monomers and are involved in the storage and transmission of genetic material.
The two nucleic acids to know for the AP Biology exam are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
Structures like that shown below are found in which of the four major classes of organic macromolecules?
The structure pictured here is a nucleotide, as is evident from its nitrogenous base, sugar, and phosphate group. Nucleotides are the monomers ("building blocks") that form nucleic acids, including DNA and RNA.
A student is analyzing an unknown biomolecule. He knows that the molecule includes covalent bonds and that it is not a lipid. He is also certain that the molecule contains carbon, hydrogen, and phosphorus, although it may also include other elements. This biomolecule is most likely a:
All four of the main classes of organic macromolecule include covalent bonds, so that piece of information is unhelpful. However, only nucleic acids and (some) lipids can contain phosphorus. Since we are told that this molecule is not a lipid, it must be a nucleic acid.