Chemistry
Peptides
Peptides are short chains of amino acids linked by peptide bonds. They are fundamental building blocks of proteins and play crucial roles in various biological processes. In chemistry, peptides are studied for their structure, synthesis, and potential applications in drug development and materials science.
Written by Perlego with AI-assistance
Related key terms
1 of 5
4 Key excerpts on "Peptides"
eBook - PDFTherapeutic Peptides and Proteins
Formulation, Processing, and Delivery Systems, Third Edition
- Ajay K. Banga(Author)
- 2015(Publication Date)
- CRC Press(Publisher)
37 2 Structure and Analysis of Therapeutic Peptides and Proteins This chapter discusses the unique structural and analytical aspects of Peptides and proteins. A detailed discussion of these topics is beyond the scope of this book. Instead, the discussion will emphasize the basic concepts that will have application to the rest of the book as formulation, pharmaceutical processing, and delivery of therapeutic Peptides and proteins are discussed. 2.1 AMINO ACIDS: BUILDING BLOCKS OF PROTEINS The 20 different naturally occurring amino acids are the building blocks of Peptides and proteins. Amino acids are commonly represented by three-letter abbreviations, but sometimes, one-letter abbreviations are also used. Although the human body needs all 20 amino acids, it cannot synthesize some amino acids known as essential amino acids. Essential amino acids must be obtained from the diet. As the name implies, an amino acid contains an amino group and an acid group in the same mol-ecule. Amino acids have a central carbon atom (alpha-carbon) to which are attached a carboxyl group, an amino group, a hydrogen atom, and a side chain. Different amino acids differ with respect to the side chain (R) only: H | R ¾ C ¾ COO – | NH 3 + Gly is the simplest amino acid with no side chain. The side chain of Pro is unique in that it is bonded covalently to the nitrogen atom of the peptide group. The amide forms of Asp and Glu (Asn and Gln, respectively) occur naturally and are incorpo-rated into proteins. Ionizable side chains of amino acids vary from acidic to basic. Aspartic and glutamic acids have a negative charge, while lysine and arginine have a positive charge at the physiological pH of 7.4. The imidazole group in histidine carries a partial positive charge at pH 7.4. Serine and threonine have side chains that carry no charge at any pH, but are polar in nature. In contrast, tryptophan, phenyl-alanine, and isoleucine have side chains that are more hydrocarbon like in character.
eBook - PDF- David R. Klein(Author)
- 2021(Publication Date)
- Wiley(Publisher)
25.1 Introduction to Amino Acids, Peptides, and Proteins 1195 25.1 Introduction to Amino Acids, Peptides, and Proteins Throughout this book, particularly in the BioLinks boxes, we have explored the relationship between the structure of a compound and its medicinal activity. The relationship between structure and activ- ity is perhaps most striking for biological molecules called proteins. Proteins are polymers that are assembled from amino acid monomers that have been linked together, much like jigsaw puzzle pieces (Figure 25.1). Each amino acid contains an amino group (shown in red) and a carboxylic acid group DO YOU REMEMBER? Before you go on, be sure you understand the following topics. If necessary, review the suggested sections to prepare for this chapter: • Designating Configuration Using the Cahn–Ingold–Prelog System (Section 5.3) • Structure and Properties of Carboxylic Acids (Section 20.3) • Nucleophilic Acyl Substitution (Section 20.7) • Properties of Amines (Section 22.3) Take the DO YOU REMEMBER? QUIZ in the online course to check your understanding. FIGURE 25.1 An illustration showing how amino acids serve as building blocks for proteins. H N H C C R O OH H Amino acid H N H C C R O OH H Amino acid Protein N H C C R O H N H C C R O H N H C C R O H OH C C R O H N H H N H C C R O H (shown in blue). It is the presence of these two functional groups that enables amino acids to link together. An amino acid can have any number of carbon atoms separating the two functional groups, but of particular interest are the alpha (α) amino acids in which the two functional groups are sepa- rated by exactly one carbon atom. H N H C C R O OH H COOH R H 2 N An α-amino acid Functional groups are separated by only one carbon atom. Amino acids of this type are called α-amino acids because the amino group is connected to the car- bon atom that is alpha (α) to the carboxylic acid group.
eBook - PDF- David R. Klein(Author)
- 2016(Publication Date)
- Wiley(Publisher)
25 25.1 Introduction to Amino Acids, Peptides, and Proteins 25.2 Structure and Properties of Amino Acids 25.3 Amino Acid Synthesis 25.4 Structure of Peptides 25.5 Sequencing a Peptide 25.6 Peptide Synthesis 25.7 Protein Structure 25.8 Protein Function Amino Acids, Peptides, and Proteins DID YOU EVER WONDER . . . how crime-scene investigators are able to find invisible fingerprints and render them visible? A fingerprint can often be the most important piece of evidence left behind at the scene of a crime. Police investigators use a variety of methods to visualize fingerprints. One such method involves the use of a chemical agent called ninhydrin, which reacts with the amino acids present in the fingerprint to produce colored compounds that can be seen. But what are amino acids, why are they present in our fingerprints, and what function do amino acids serve? In this chapter, we will explore the structure and properties of amino acids, and we will see how they function as the building blocks that nature employs to assemble important biological com- pounds called Peptides and proteins. These compounds serve a wide array of functions, as we will see later in this chapter. This chapter focuses on the structure, properties, function, and synthesis of amino acids, Peptides, and proteins. 1148 CHAPTER 25 Amino Acids, Peptides, and Proteins DO YOU REMEMBER? Before you go on, be sure you understand the following topics. If necessary, review the suggested sections to prepare for this chapter: • Designating Configuration Using the Cahn–Ingold–Prelog System (Section 5.3) • Structure and Properties of Carboxylic Acids (Section 20.3) • Nucleophilic Acyl Substitution (Section 20.7) • Properties of Amines (Section 22.3) Take the DO YOU REMEMBER? QUIZ in to check your understanding.
eBook - PDF- David R. Klein(Author)
- 2020(Publication Date)
- Wiley(Publisher)
When amino acids join together to form a peptide, the order in which they are connected is important. For example, consider a simple dipeptide made by joining alanine and gly- cine. The peptide bond can be formed between the COOH group of alanine and the NH 2 group of glycine, or from the COOH group of glycine and the NH 2 group of alanine. Ala-Gly Glycine Alanine N OH O H H CH 3 O OH H 2 N N O H OH O CH 3 H 2 N Glycine Alanine Gly-Ala H 2 N OH O CH 3 O OH N H H CH 3 H 2 N O OH N H O These two diPeptides are not the same compound. They are, in fact, constitutional isomers. Peptide chains always have an amino group on one end, called the N terminus, and a COOH group on the other end, called the C terminus (Figure 25.4). By convention, Peptides are always drawn with the N terminus on the left side. SKILLBUILDER LEARN the skill 25.3 DRAWING A PEPTIDE Draw a bond-line structure showing the tripeptide Phe-Val-Trp (assume that all three residues are L amino acids). N H C C R O H N H C C R O H N H C C R O H OH C C R O H N H H N H C C R O H N terminus C terminus FIGURE 25.4 The N terminus and C terminus of a peptide chain. The sequence of amino acid residues in a peptide can be abbreviated with one- or three-letter abbreviations, starting with the N terminus. For example, a dipeptide of glycine and alanine can be written as follows: O CH 3 OH N H O H 2 N Glycine residue Alanine residue N terminus C terminus Gly Ala Simple peptide chains will have one N terminus and one C terminus. For example, consider the following decapeptide, for which the alanine residue is the N terminus and the leucine residue is the C terminus: N terminus C terminus Try Glu Gly Phe Met Cys Cys Pyr Leu Ala 25.4 Structure of Peptides 1153 SOLUTION Begin by drawing a peptide comprised of three residues with the N terminus on the left and the C terminus on the right. O H N N H O OH O R R R H 2 N N terminus C terminus Next, identify the side chain (R group) associated with each residue.
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
