Introduction to Biochemistry and Biomolecules

Carbon is the "LEGO brick" of life because of its incredible flexibility. It can form strong covalent bonds with itself to create long chains, rings, and branched structures. Furthermore, carbon readily bonds with other essential elements to form the complex molecules necessary for life. A helpful way to remember the most abundant elements in living organisms is the acronym CHNOPS:

• C: Carbon
• H: Hydrogen
• N: Nitrogen
• O: Oxygen
• P: Phosphorus
• S: Sulfur

While these six elements are the most abundant, organisms also require trace elements in tiny amounts to function. For instance, even though iron ($Fe$) is present in small quantities, it is essential for hemoglobin to carry oxygen in your blood.

The Four Major Biomolecules

A biomolecule is a molecule found in a living organism that performs a specific biological function. There are four primary classes of biomolecules that you must recognize:

Chemical Bonding: The Language of Molecules

To understand how these biomolecules are shaped and how they react, we must understand the bonds that hold them together.

Ionic and Covalent Bonds

Atoms contain electrons. If an atom loses or gains electrons, it becomes an ion:

• Cation: A positively charged ion (lost electrons).
• Anion: A negatively charged ion (gained electrons).

An ionic bond is the attraction between these oppositely charged ions (e.g., $Na^+$ and $Cl^-$). In contrast, a covalent bond occurs when atoms share electrons.

Covalent bonds can be:

• Nonpolar: Electrons are shared equally (50/50).
• Polar: Electrons are shared unequally because one atom attracts them more strongly (e.g., Oxygen in water).

Study Tool: The Octet Rule When drawing structures, remember the common number of bonds these atoms form:

• $H = 1$ bond
• $O = 2$ bonds
• $N = 3$ bonds
• $C = 4$ bonds

Hydrogen Bonds

A hydrogen bond is not a permanent bond like a covalent bond; rather, it is an attraction between partially charged parts of molecules. This occurs when a hydrogen atom, already covalently bonded to an electronegative atom (like $O$ or $N$), is attracted to another electronegative atom. Hydrogen bonds are critical for the structure of water, proteins, and DNA.

Metabolism: The Engine of Life

All the chemical reactions occurring within a living organism to sustain life are collectively known as metabolism. Metabolism is not a single process but a balance of two opposing pathways:

1. Anabolism (The "Build-up"): The synthesis of complex molecules from simpler ones. For example, using amino acids to build a protein.
2. Catabolism (The "Break-down"): The breakdown of complex molecules into simpler ones to release energy or provide building blocks, such as digesting food.

In short: $\text{Metabolism} = \text{Anabolism} + \text{Catabolism}$

By understanding these chemical relationships, we can begin to understand the complex machinery that keeps us alive.