Proteins: Structure, Functions, and Properties

Proteins

Proteins are biopolymers that play a central role in various biological processes. They are made up of amino acids, which are bonded together through peptide links. Proteins are incredibly diverse, serving numerous functions in cells such as providing structure, acting as signaling agents, and participating in enzymatic reactions.

Building Blocks of Proteins

Amino Acids

Proteins are constructed from amino acids, which are organic compounds consisting of a central carbon atom bound to an amino group (that acts as a base), a carboxyl group (an acid group), a hydrogen atom, and a variable chemical group known as a side chain. There are 20 standard amino acids found in nature, which can be classified into two broad categories: α-amino and β-amino acids.

Peptide Bonds

During protein formation, amino acids are connected through peptide bonds, which are formed when the amide group (-CONH-) of one amino acid binds to the carbonyl group (-C=O) of another amino acid. This process involves the removal of a water molecule (dehydration synthesis).

Types and Functions of Proteins

Proteins perform a multitude of tasks in cells and organisms. Some common types of proteins include:

Enzymes

Enzymes are catalysts that speed up biochemical reactions by lowering the activation energy required for a reaction to occur. They recognize specific substrates (molecules involved in their respective reactions) and can either break down, link up, or rearrange them. For instance, salivary amylase is an enzyme found in your body that breaks down starch into smaller sugars, contributing to our perception of sweetness in starchy foods.

Structural Proteins

Structural proteins provide support and shape to cells and tissues. Examples include collagen, which provides strength and stability to bones, tendons, and skin, and actin, which helps maintain cell shape.

Signal Transduction Proteins

These proteins transmit signals from one part of a cell to another. They are often involved in sensory response pathways and play a crucial role in coordinating cellular activities in response to external stimuli.

Protein Structure and Properties

Proteins have complex structures that emerge from a folding process driven by noncovalent interactions between amino acid side chains. These structures, along with the linear sequence of amino acids within a protein, determine its function. The primary structure of a protein refers to the arrangement of amino acids in a chain, while secondary and tertiary structures refer to folded sections and overall three-dimensional arrangements of the protein chain, respectively. Factors such as hydrogen bonds, ionic bonds, and van der Waals forces contribute to protein stability and conformations.