Biochemistry

Biochemistry is the chemistry of life, a bridge between biology and chemistry that studies how complex chemical reactions give rise to life. It is a hybrid branch of chemistry which specialises in the chemical processes in living organisms. This article only discusses terrestrial biochemistry (carbon- and water-based), as all the life forms we know are on Earth. Since life forms alive today are believed to have descended from the same common ancestor, they naturally have similar biochemistries, even for matters which would appear to be essentially arbitrary, such as the genetic code or handedness of various biomolecules. It is unknown whether alternate biochemistries are possible or practical.

Lipids

The term lipid comprises a diverse range of molecules and to some extent is a catchall for relatively water-insoluble or nonpolar compounds of biological origin, including waxes, fatty acids, fatty-acid derived phospholipids, sphingolipids, glycolipids and terpenoids, such as retinoids and steroids. Some lipids are linear aliphatic molecules, while others have ring structures. Some are aromatic, while others are not. Some are flexible, while others are rigid.

Related Topics:
Molecules - Nonpolar - Wax - Fatty acid - Steroids - Aliphatic - Aromatic

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Most lipids have some polar character in addition to being largely nonpolar. Generally, 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). In the case of phospholipids, the polar groups are considerably larger and more polar, as described below.

Related Topics:
Polar - Hydrophobic - Hydrophilic - Amphiphilic - Cholesterol - Hydroxyl

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