Peptides are short chains of amino acids linked together by peptide bonds. Amino acids, when joined together in a specific sequence, they form peptides. Peptides can range in length from just a few amino acids to several dozen.
Amino acids are organic compounds that serve as the building blocks of proteins. They consist of an amino group (-NH2), a carboxyl group (-COOH), and a side chain (R group) all attached to a central carbon atom.
There are 20 different amino acids commonly found in proteins, each with a unique side chain that imparts specific chemical properties. Amino acids also play essential roles beyond protein synthesis, acting as precursors for various molecules involved in metabolism and signaling pathways. They are crucial for maintaining the overall health and functioning of organisms.
A few examples of Amino Acids
- Alanine (Ala): It has a simple side chain consisting of a methyl group (-CH3).
- Glycine (Gly): It is the simplest amino acid with just a hydrogen atom as its side chain.
- Valine (Val): It has a branched side chain made up of three carbon atoms.
- Leucine (Leu): It also has a branched side chain, similar to valine, but with an additional methyl group.
- Phenylalanine (Phe): It has an aromatic side chain consisting of a benzene ring.
- Tryptophan (Trp): It is another aromatic amino acid with a larger side chain containing a fused ring system.
- Serine (Ser): It has a hydroxyl group (-OH) as its side chain.
- Cysteine (Cys): It contains a thiol group (-SH) in its side chain, making it capable of forming disulfide bonds.
- Aspartic acid (Asp): It has a carboxyl group (-COOH) in its side chain, making it acidic.
- Lysine (Lys): It has a long, positively charged side chain containing an amino group (-NH2).
Peptide bonds are covalent chemical bonds that connect amino acids together in proteins and peptides. They form through a condensation reaction between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of another amino acid.
During this reaction, a water molecule is released, and the carboxyl carbon forms a bond with the amino nitrogen, resulting in the formation of a peptide bond. Peptide bonds have a specific structure in which the carbon atom from the carboxyl group and the nitrogen atom from the amino group are connected by a double bond, creating a rigid and planar structure.
These bonds play a crucial role in determining the primary structure of proteins and the folding of the polypeptide chain into its functional three-dimensional structure. A carboxyl group (-COOH) is a functional group consisting of a carbon atom (C) double-bonded to an oxygen atom (O) and single-bonded to a hydroxyl group (-OH).
It is named as such because it is composed of a carbonyl group (C=O) and a hydroxyl group. The carboxyl group is acidic due to the presence of the hydroxyl group, which can donate a proton (H+), resulting in the formation of a carboxylate ion (-COO-). Carboxyl groups are commonly found in carboxylic acids and play vital roles in various biological processes, including enzyme-catalyzed reactions and protein folding.
They also have diverse applications in the pharmaceuticals, food, and industrial sectors. Understanding the properties and reactivity of carboxyl groups is essential for the synthesis and manipulation of organic compounds.
Peptides play crucial roles in various biological processes and have diverse functions in the body. They can act as hormones, neurotransmitters, enzymes, and signaling molecules, among other roles. Some peptides are involved in regulating physiological processes such as growth, metabolism, and immune response.
Some examples of Peptides
- Insulin: Insulin is a peptide hormone consisting of two peptide chains linked together by disulfide bonds. It plays a crucial role in regulating blood sugar levels.
- Oxytocin: Oxytocin is a peptide hormone involved in social bonding, childbirth, and lactation. It consists of nine amino acids and is often referred to as the “love hormone.”
- Glutathione: Glutathione is a peptide composed of three amino acids (glutamate, cysteine, and glycine). It acts as an antioxidant and plays a vital role in cellular detoxification processes.
- Antimicrobial peptides (AMPs): AMPs are a diverse group of peptides that are part of the innate immune system. They help protect against various pathogens by directly killing or inhibiting their growth.
- Melanotan II: Melanotan II is a synthetic peptide that can stimulate skin pigmentation. It is sometimes used for tanning purposes.
- BPC-157: BPC-157 is a peptide derived from a protein found in gastric juice. It has been investigated for its potential therapeutic effects, including promoting healing and reducing inflammation.
- Angiotensin II: Angiotensin II is a peptide hormone that plays a crucial role in regulating blood pressure and fluid balance in the body. It is formed through the action of enzymes on angiotensin I.
- Leucine-enkephalin: Leucine-enkephalin is an endogenous opioid peptide that acts as a natural painkiller. It consists of five amino acids and is involved in modulating pain perception.
One well-known example of a peptide hormone is insulin, which regulates blood sugar levels. Insulin is a peptide hormone composed of two peptide chains linked together by disulfide bonds[1]. Another example is oxytocin, often referred to as the “love hormone,” which plays a role in social bonding and childbirth. Peptides can also be used therapeutically. Due to their ability to specifically interact with cellular targets, peptides have attracted considerable attention in drug development.
Peptide-based drugs are designed to mimic or inhibit the activity of natural peptides in the body. For example, some peptide-based drugs are used in the treatment of cancer, diabetes, and cardiovascular diseases. In recent years, peptide research has expanded into the field of cosmetic science.
Peptides are now being used in skin care products for their potential to enhance collagen production, improve skin elasticity, and reduce the appearance of wrinkles. These peptides, often referred to as “cosmeceuticals,” are designed to be applied topically and penetrate the skin to deliver their benefits.
Peptides in Food
- Eggs
- Milk
- Meat
- Fish and shellfish
- Beans and lentils
- Soy
- Oats
- Flaxseed
- Hemp seeds
- Wheat
It’s important to note that while peptides have shown promise in various applications, including therapeutics and skincare, further research is still ongoing to explore their full potential and optimize their efficacy.
Footnotes
- Disulfide bonds are covalent bonds formed between two cysteine amino acids in proteins, where the sulfur atoms from each cysteine form a bond. These bonds are formed through an oxidation reaction between the sulfhydryl (-SH) groups of cysteine residues, resulting in the release of two hydrogen atoms. Disulfide bonds play a crucial role in stabilizing the three-dimensional structure of proteins by creating cross-links between different regions of the polypeptide chain. They contribute to the folding, stability, and functional conformation of proteins, particularly those secreted or exposed to oxidative environments. Disulfide bonds can be reversible or irreversible, depending on the conditions. The formation and arrangement of disulfide bonds are vital for maintaining protein structure and function, and they are often involved in protein folding and protein-protein interactions. [Back]
Further Reading
Sources
- “What Are Peptides?” (May 02, 2023) https://www.webmd.com/a-to-z-guides/what-are-peptides
- Riviere, G. (2017). Molecular signaling through G protein-coupled receptors and the extracellular signaling. Molecular Pharmacology, 92(6), 631-638.
- Henninot, A., Collins, J. C., & Nuss, J. M. (2018). The current state of peptide drug discovery: back to the future?. Journal of medicinal chemistry, 61(4), 1382-1414.
- Babizhayev, M. A., & Yegorov, Y. E. (2015). Telomere attrition in human lens epithelial cells associated with oxidative stress provides a new therapeutic target for the treatment, dissolving and prevention of cataract with N-acetylcarnosine lubricant eye drops. The EPMA journal, 6(1), 21.
- Huang, Y. J., Huang, Y. T., Wang, S. Y., et al. (2021). Growth Hormone-Releasing Peptides and their Analogues: Current Research Progress and Future Perspectives. Journal of the Chinese Medical Association, 84(3), 271-280.
- “What to know about peptides for health” (October 16, 2019) https://www.medicalnewstoday.com/articles/326701
