What is a peptide?
Peptides are short chains of amino acids linked by peptide bonds. They are essentially small proteins, typically containing 2-50 amino acids. Some key features of peptides include:
- Size: Peptides are smaller than proteins, which typically contain >50 amino acids. The short size allows peptides to have unique biological activities compared to larger proteins.
- Function: Peptides play diverse biological roles, including as hormones (e.g. insulin), neurotransmitters (e.g. endorphins), and antimicrobial agents. Some peptides help give structure/support, while others are involved in cell signaling, immune function, etc.
- Production: Peptides can be naturally produced by the body or synthetically manufactured. Many peptides found naturally are cleaved from larger protein precursors by proteases. Bioengineered peptides are commonly used as medicines.
- Structure: The sequence and number of amino acids in a peptide determine its 3D structure, which drives its function. Specific structural motifs like beta-sheets, alpha helices, and turns/loops are common.
The key distinction between peptides and proteins is size. Proteins are typically much larger than peptides, containing >50 amino acids. The compact size of peptides allows them to access targets inside cells and exhibit biological activities that bulky proteins cannot. However, size is not the only difference. While some peptides and proteins may share similar sequences or structures, their functional roles in the body can vary greatly.
Some examples will help illustrate the diversity of peptides:
- Insulin: This peptide hormone, produced in the pancreas, regulates blood sugar levels. It contains 2 short polypeptide chains with interchain disulfide bridges.
- Glutathione: An antioxidant peptide made internally from three amino acids - glutamate, cysteine, glycine. It protects cells from oxidative damage.
- Beta-amyloid: Peptide fragments of a larger protein associated with Alzheimer's disease. These peptides misfold and accumulate in plaques in the brain.
In summary, peptides are short chains of amino acids that play important and varied biological roles. Their compact size allows unique functions not seen in larger proteins. Peptides exist naturally in the body but can also be produced synthetically as medicines. They exhibit immense diversity in sequence, structure, and function across different organisms. Understanding peptides provides insight into health and disease.