The Four Major Classes of Biomolecules

Biomolecules are compounds that center around the element, carbon.  Carbon, because of its valence structure, is actually quite versatile and probably responsible for the great variation of life on this planet.  In today’s post we are going to look at the four major classes of biomolecules.  For each class, pay special attention to the structure and function of these biomolecules.

Proteins make up the majority of biomolecules present in a cell.  These molecules have enormous variation.  Proteins are responsible for many enzymatic functions in the cell and play an important structural role .  Proteins are composed of subunits called amino acids.  There are 21 different types of amino acids (including the less known selenocysteine).  It would be very important for the student to know the different functional groups that make up a single amino acid.  Amino acids are composed of a carboxyl group and an amino group bound to a central carbon atom.  A hydrogen atom occupies the third bonding site on the carbon and a variable “R” group occupies the fourth.   This R group gives the amino acid special properties that are responsible for making proteins functional.  Long chains of amino acids, formed by peptide bonds between each amino acid, form a polypeptide. More on protein structure can be found at this blog post.

The structure of serine, an amino acid

Nucleic acids are the second type of biomolecules that we will discuss.  These molecules are responsible for all of our genetic information.  You are probably very familiar with DeoxyriboNucleic Acid (DNA) and RiboNucleic Acid (RNA).  Nucleic acids are formed from subunits called nucleotides.  There are 5 different types of nucleotides in the cell; Adenine, Thymine, Guanine, Cytosine and Uracil.  Each nucleotide is composed of a nitrogenous base, a 5-carbon sugar, and 3 phosphate groups.  The bonds that form between nucleotides are called phosphodiester bonds.  Nucleotides are responsible for more than just composing DNA and RNA, as ATP is a nucleotide and is also the energy currency of the cell!  Click here for in-depth post dedicated to the structure of DNA.

Cytosine, a nucleotide

Carbohydrates provide an energy source for the cell and also may play a structural role.  The simplest subunit of a carbohydrate is a monosaccharide.  The structure of the glucose molecule is a good representation of carbohydrate subunits, also called a monomer.

Glucose, the building block of carbohydrates

The final class of biomolecules are lipids.  Lipids are composed of long hydrocarbon chains (-CH2-).  These molecules hold an incredible amount of energy and are therefore energy storage molecules.  Because of some pretty neat biochemical properties (hydrocarbons are hydrophobic), lipids are the major component of cell membranes.  Cholesterol and other sterols are also types of lipids and are necessary components of cell membranes.

A short chain fatty acid

If your teacher drew these four molecules on an exam, would you be able to identify which is which?

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