Biological Macromolecules and Carbon Bonding – Study Notes

Biological macromolecules are large molecules essential for life, built from smaller organic molecules.
Four major classes: carbohydrates, lipids, proteins, and nucleic acids.
Collectively, these macromolecules make up the majority of a cell's dry mass.
They are organic, meaning they contain carbon and are bound to hydrogen, and they may also contain oxygen, nitrogen, and other minor elements.

Life is often described as carbon-based; carbon atoms bonded to carbon or to other elements form the fundamental components of many molecules found in living things.
While other elements play important roles, carbon is the foundational element for molecules in living organisms because of its bonding properties.

Carbon contains four electrons in its outer shell.
Therefore, carbon can form four covalent bonds with other atoms or molecules.
The simplest organic carbon molecule is methane: $ext{CH}_4$ , in which four hydrogen atoms bind to a carbon atom.
- Methane example: $ext{CH}_4$ .
The ability to form multiple covalent bonds is what enables carbon to build diverse structures.
In notation: outer shell electrons = $4$ , bonding capacity = $4$ .

Any of the hydrogen atoms in methane can be replaced with another carbon atom covalently bonded to the first carbon atom.
This replacement leads to long and branching chains of carbon compounds.
The carbon atoms may also bond with other elements, such as nitrogen, oxygen, and phosphorus.
Molecules may form rings, and these rings can link with other rings.
This versatility in bonding underpins the diversity of biological macromolecules and their wide range of functions.

The diversity of molecular forms in living things is largely due to carbon's ability to form multiple bonds with itself and with other elements.

Stearic acid: a molecule with a long chain of carbon atoms (long hydrocarbon chain).
Glycine: contains carbon, nitrogen, oxygen, and hydrogen atoms; a component of proteins.
Glucose: has a ring structure made up of carbon atoms and contains one oxygen atom.

Biological macromolecules rely on carbon's tetravalence to construct complex, varied structures.
The combination of long chains, branching, ring formations, and incorporation of heteroatoms (N, O, P) enables a vast array of functional macromolecules.
Understanding carbon bonding is foundational for studying biochemistry, organic chemistry, and the structure–function relationships of biomolecules.

Methane: $ext{CH}_4$
Carbon outer shell electrons: $4$
Carbon bonding capacity (valence): $4$
The four major classes of macromolecules: carbohydrates, lipids, proteins, nucleic acids