Editing Biochemistry (section)

===Lipids===
{{Main|Lipid|Glycerol|Fatty acid}}

[[File:Common lipid types.svg|class=skin-invert-image|thumb|Structures of some common lipids. At the top are [[cholesterol]] and [[oleic acid]].<ref>[[#Stryer|Stryer]] (2007), p. 328.</ref> The middle structure is a [[triglyceride]] composed of [[oleate|oleoyl]], [[stearic acid|stearoyl]], and [[palmitate|palmitoyl]] chains attached to a [[glycerol]] backbone. At the bottom is the common [[phospholipid]], [[phosphatidylcholine]].<ref>[[#Voet|Voet]] (2005), Ch. 12 Lipids and Membranes.</ref>]]

[[Lipid|'''Lipids''']] comprise a diverse range of [[molecules]] and to some extent is a catchall for relatively water-insoluble or [[nonpolar]] compounds of biological origin, including [[wax]]es, [[fatty acid]]s, fatty-acid derived [[phospholipid]]s, [[sphingolipid]]s, [[glycolipid]]s, and [[terpenoid]]s (e.g., [[retinoid]]s and [[steroid]]s). Some lipids are linear, open-chain [[aliphatic]] molecules, while others have ring structures. Some are [[aromatic]] (with a cyclic [ring] and planar [flat] structure) while others are not. Some are flexible, while others are rigid.<ref>{{Citation |last1=Ahmed |first1=Saba |title=Biochemistry, Lipids |date=2023 |url=http://www.ncbi.nlm.nih.gov/books/NBK525952/ |work=StatPearls |access-date=2023-11-30 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=30247827 |last2=Shah |first2=Parini |last3=Ahmed |first3=Owais}}</ref>

Lipids are usually made from one molecule of [[glycerol]] combined with other molecules. In [[triglyceride]]s, the main group of bulk lipids, there is one molecule of glycerol and three [[fatty acid]]s. Fatty acids are considered the monomer in that case, and may be [[Saturated and unsaturated compounds|saturated]] (no [[double bond]]s in the carbon chain) or unsaturated (one or more double bonds in the carbon chain).{{cn|date=April 2023}}

Most lipids have some [[Polar molecule|polar]] character and are largely nonpolar. In general, the bulk of their structure is nonpolar or [[hydrophobic]] ("water-fearing"), meaning that it does not interact well with polar solvents like [[water]]. Another part of their structure is polar or [[hydrophilic]] ("water-loving") and will tend to associate with polar solvents like water. This makes them [[amphiphilic]] molecules (having both hydrophobic and hydrophilic portions). In the case of [[cholesterol]], the polar group is a mere –OH (hydroxyl or alcohol). {{cn|date=March 2024}}

In the case of phospholipids, the polar groups are considerably larger and more polar, as described below.

Lipids are an integral part of our daily diet. Most [[oil]]s and [[milk product]]s that we use for cooking and eating like [[butter]], [[cheese]], [[ghee]] etc. are composed of [[fat]]s. [[Vegetable oil]]s are rich in various [[polyunsaturated fatty acid]]s (PUFA). Lipid-containing foods undergo digestion within the body and are broken into fatty acids and glycerol, the final degradation products of fats and lipids. Lipids, especially [[phospholipid]]s, are also used in various [[pharmaceutical product]]s, either as co-solubilizers (e.g. in parenteral infusions) or else as [[drug carrier]] components (e.g. in a [[liposome]] or [[transfersome]]).