The Building Blocks of Proteins Amino Acids, Peptides, and Polypeptides

Amino Acids Have Both Acid and Base Properties Aromatic Amino Acids Absorb Light in the Near-Ultraviolet 

All Amino Acids except Glycine Show Asymmetry Peptides and Polypeptides 

Determination of Amino Acid Composition of Proteins Determination of Amino Acid Sequence of Proteins Chemical Synthesis of Peptides and Polypeptides 

Amino acids have common features that permit them to be linked together into polypeptide chains and uncommon features that give each polypeptide chain its unique character. 

Proteins are the most abundant of cellular components. They include enzymes, antibodies, hormones, transport molecules, and even components for the cytoskeleton of the cell itself. Proteins are also informational macromolecules, the ultimate heirs of the genetic information encoded in the sequence of nucleotide bases within the chromosomes. Structurally and functionally, they are the most diverse and dynamic of molecules and play key roles in nearly every biological process. Proteins are complex macromolecules with exquisite specificity each is a specialized player in the orchestrated activity of the cell. Together they tear down 

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The Building Blocks of Proteins Amino Acids, Peptides, and Polypeptides 49 The Three-Dimensional Structures of Proteins 72... 

Part 2, Protein Structure and Function, contains four chapters that relate to the structures and functions of proteins. In chapter 3, The Building Blocks of Proteins Amino Acids, Peptides, and Polypeptides, we discuss basic structural and chemical properties of amino acids, peptides and polypeptides. In chapter 4, The Three-Dimensional Structures of Proteins, we describe how and why polypeptide chains fold into long fibrous molecules in some cases, or into compact globular molecules in other cases. In chapter... 

In the first three chapters of part 2 we discuss the basic structural and chemical properties of proteins. In this chapter we concentrate on the structural and chemical properties of amino acids, peptides, and polypeptides—the building blocks of proteins. From our presentation you will learn the following ... 

Amino acids are the building blocks of proteins. A single protein consists of one or more chains of amino adds strung end to end by peptide bonds Hence the name polypeptide. You must be able recognize the structure of an amino acid and a polypeptide. A peptide bond creates the functional group known as an amide (an amine connected to a carbonyl carbon). It is formed via condensation of two amino acids. The reverse reaction is the hydrolysis of a peptide bond. 

We begin with the structure and preparation of the 20 most coimnon amino acids, the building blocks of proteins. We then show how amino acids are linked by peptide bonds in the three-dimensional structure of hanoglobin and other polypeptides. Some proteins contain thousands of amino acids, but we shall see how to determine the sequence of amino acids in many polypeptides and synthesize these molecules in the laboratory. Finally, we consider how other polymers, the nucleic adds DNA and RNA, direct the synthesis of proteins in nature. 

This chapter focuses on supramolecular assemblies that are formed using a variety of de novo designed peptide-based tectons. A brief introdnction to amino acids (the building blocks of peptides and proteins) is given, followed by a discussion of the basic structures that polypeptide chains of amino acids can adopt. These structures form the basis of the supramolecular assemblies that will be reviewed. The subsequent sections provide details of recent examples of repetitive, effectively infinite, and discrete snpramolecular peptide-based assemblies, and also a dis-cnssion of their potential applications. 

The properties of polypeptides and proteins are determined to a large extent by the chemistry of the side chain groups, which may be summarized briefly as follows. Glycine in a peptide permits a maximum of conformational mobility. The nine relatively nonpolar amino acids-alanine, valine, leucine, isoleucine, proline, methionine, phenylalanine, tyrosine, and tryptophan-serve as building blocks of characteristic shape. Tyrosine and tryptophan also participate in hydrogen bonding and in aromatic aromatic interactions within proteins. 

The protein amino acids are the basic building blocks for all peptide chains (amino acid polymers and oligomers) and protein chains (a protein is a large polypeptide), which make up the structure of an enormous number of biological molecules including enzymes. The chains are held together by peptide links (amide... 

Posttranslational modifications considerably extend the chemical diversity of the building blocks forming polypeptide chains. A good deal of effort has been directed toward understanding how the individual amino acid derivative affects the CTI of neighboring prolyl bonds in peptides and proteins. 

This chapter will introduce polymer systems containing either naturally occurring maaomolecules (polysaccharides, proteins, DNA) or their subunits (bioanalogous molecules, amino acids, short peptides and peptide derivatives, polypeptides, polynucleotides), respectively. The natural building blocks can be connected by covalent bonds or by self-assembly and either can be used alone (see, e.g.. Section 5.4) or in combination with synthetic polymer units (biohybrids). Alternatively the building block itself may be a hybrid of a natural and synthetic molecule (bioconjugate cf. Section 3.5), as, for instance, a PEG-peptide conjugate. 

All proteins are composed of amino acids that are covalently linked by peptide (amide) bonds into long polypeptide chains. Twenty different amino acids are known to serve as the building blocks in all proteins. The amino acid sequence of a naturally occiu-ring polypeptide (i.e., the type, number, and order of each amino acid in the chain) is genetically determined. Two or more polypeptide chains can be covalently linked together by, most commonly, disulfide bonds. 

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