Biochemistry

TLO: Identify four types of organic molecules essential to human functioning

Organic compounds typically consist of groups of carbon atoms covalently bonded to hydrogen, usually oxygen, and often other elements as well. They are found throughout the world, in soils and seas, commercial products, and every cell of the human body. The four types most important to human structure and function are carbohydrates, lipids, proteins, and nucleic acids. Before exploring these compounds, you need to first understand the chemistry of carbon.

2.1 The chemistry of carbon

What makes organic compounds unique is the chemistry of their carbon core. Recall that carbon atoms have four electrons in their valence shell, and that the octet rule dictates that atoms tend to react in such a way as to complete their valence shell with eight electrons. Carbon atoms do not complete their valence shells by donating or accepting four electrons. Instead, they readily share electrons via covalent bonds.

Commonly, carbon atoms share with other carbon atoms, often forming a long carbon chain referred to as a carbon skeleton. When they do share, however, they do not share all their electrons exclusively with each other. Rather, carbon atoms tend to share electrons with a variety of other elements, one of which is always hydrogen. Carbon and hydrogen groupings are called hydrocarbons.

Also attached to the carbon skeleton are distinctive functional groups. A functional group is a group of atoms linked by strong covalent bonds that determine the chemical behavior of any particular compounds.

Figure 1 Major functional group of organic materials.

Small organic molecules can combine into very large molecules that are called macromolecules. Macromolecules are usually polymers. A polymer is a large molecule formed by the covalent bond of either identical or similar small building-block molecules called monomers.



             Molecules that have the same molecular formula but different structures are called isomers. For instance, the molecular formulas for the sugars glucose and fructose are both C₆H₁₂O₆. Due to certain individual atoms positioned differently along the carbon skeleton giving them sugars different chemical properties.

Figure 2 Glucose and fructose are considered to be isomers because they share the same molecular formula but certain individual atoms are positioned differently.  (source: https://www.vedantu.com/)