Fatty Acids and the Code Talkers
Carbohydrates and proteins may get all the press but two other organic compounds, lipids and nucleic acids, are fundamental to cellular biology—and therefore to human life.
Lipids
Lipids are hydrocarbon molecules used in plasma membranes and for energy storage. Because they are composed of neutrally charged hydrocarbon chains, they are hydrophobic.
What keeps oil and water from mixing?
Oil is a hydrocarbon (hydrophobic substance) and will not interact with charged (polar) molecules, such as water.
Saturated versus Unsaturated Fatty Acids
Fatty acid chains are polymers of hydrocarbons, which are attached to a carboxylic acid (a compound in which a carbon atom is bonded to an oxygen atom, such as COOH-, making it a weak acid). The carbons can be attached to each other via a single bond, with the remaining bonds completed with hydrogen molecules. This would generate a saturated fatty acid in which all of the bonds of carbon are occupied by additional atoms. A straight linear fatty acid chain is generated when the carbon bonds are saturated.
However, a double bond may be present between carbons (and therefore one fewer hydrogen on each of the adjacent double-bonded carbons). This is an unsaturated fatty acid and will have a bend at each of the double-bonded regions. Any more than one double bond in a single fatty acid chain will result in a polyunsaturated fatty acid.
Saturated and unsaturated fatty acids
Eating foods that are high in saturated fats can increase your cholesterol (a waxy substance that can clog your arteries), possibly affecting your heart health. Most saturated fats come from animal sources (including meats and dairy). Unsaturated fats are considered healthier for your heart.
Phospholipids
Phospholipid is the main constituent in membranes within a cell, including the plasma, nuclear, mitochondrial (the mitochondria is the energy-producing structure in a cell), and vesicular (vesicles are structures used for storage and transport) membranes. Basically, 2 side-by-side fatty acid chains are attached at one end to a glycerol molecule. One end of the molecule is charged, making it hydrophilic, and the other end, composed of fatty acid chains, is not, making it hydrophobic. This duality is called amphipathic.
Triglycerides
Triglycerides are the storage form of energy in the body and typically are referred to as “fat.” This material is stored in fat cells called adipocytes and can be recruited when your body requires the use of a lot of energy. Releasing double the amount of energy as compared to glucose, triglycerides take longer to release energy than carbohydrates because it takes the cells longer to break down the fat and place it into the blood stream.
As the name implies, these molecules are composed of 3 (tri-) fatty acid chains attached to a glycerol molecule.
Sterols
In humans, the principal sterol (a type of fat) is cholesterol. Despite all the bad press, your body cannot function without cholesterol. It plays a critical role in the proper spacing of the plasma membrane, which gives stability to the membrane. Additionally, hormones such as estrogen and testosterone are derived from cholesterol, and are crucial to proper body function.
Nucleic Acids
Nucleic acids are necessary for each and every cell of the body. Nucleic acids exist in two forms, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). These linear molecules are the repository of genetic information (DNA) and copies of that information with which proteins are built (RNA).
DNA
Described as a double helical molecule, DNA has 2 chains held together by hydrogen bonds that can easily be separated for either DNA replication (during cell division) or RNA synthesis and transcription (the conversion of genetic information into proteins that carry out the directions).
DNA strands are composed of a few basic units. First, a sugar molecule will form part of the backbone of the strand of nucleic acid (for DNA that sugar is deoxyribose, hence the “D” in DNA). The other portion of the backbone is a phosphate group, which will link the sugars together into a long strand.
Also attached to the sugar is a nucleobase of either a purine or a pyrimidine. The purines of DNA are either adenine (A) or guanine (G) and the pyrimidines are thymine (T) and cytosine (C). The hydrogen bonds between the nucleobases are what hold the 2 DNA strands together into the double helix. The bases are always paired together: A-T and G-C. Because of their structure, the A-T pair is held together with 2 hydrogen bonds and the G-C pair with 3 hydrogen bonds. Thus, the G-C pair requires more energy to break than the A-T set. This becomes important for DNA replication and RNA synthesis (discussed in later sections).
Purines and pyrimidines—what’s the difference?
Both are nitrogenous bases. A purine has 2 carbon-nitrogen rings while a pyrimidine has a 1 carbon-nitrogen structure. They have similar functions.
RNA
Ribonucleic acid (RNA) is similar in its structure to DNA with some important differences. As the name implies, the first difference is the sugar used. For RNA, that sugar is ribose. Additionally, RNA will be synthesized as a single strand rather than a double strand. Lastly, while G, C, and A are found in RNA, T will not be present. Rather, uracil (U) is used instead.