Proteins Natural polymers composed

Proteins are natural polymers composed of a-amino acids linked by amide (peptide) bonds. Except for glycine (aminoacetic acid), protein-derived amino acids are chiral and have the L configuration. Table 17.1 lists the names, one- and three-letter abbreviations, and structures of the 20 common amino acids. Of these, eight (the essential amino acids) cannot be synthesized in the bodies of adult humans and must be ingested in food. 

Proteins are natural polymers composed of amino acids linked by peptide bonds. They can be distinguished from other natural polymers such as fats and carbohydrates by the presence of the nitrogen atom. Other heteroatoms such as sulfur and, more rarely, phosphorus may also be present. 

The remainder of this chapter will deal with natural polymers. These are large molecules, produced by plants and animals, that carry out the many life-sustaining processes in a living cell. The cell membranes of plants and the woody structure of trees are composed in large part of cellulose, a polymeric carbohydrate. We will look at the structures of a variety of different carbohydrates in Section 23.3. Another class of natural polymers are the proteins. Section 23.4 deals with these polymeric materials that make up our tissues, bone, blood, and even hair. ... 

A protein is a natural polymer that is composed of monomers called amino acids. Proteins are found in meat, milk, eggs, and legumes. 

We generally describe the structure of both synthetic and natural polymers in terms of four levels of structure primary, secondary, tertiary, and quaternary. The primary structure describes the precise sequence of the individual atoms that compose the polymer chain. For polymers that have only an average structure, such as proteins, polysaccharides, and nucleic acids, a representative chain structure is often given. 

It is very important to realise that when drugs or medicines are administered to the body there is the opportunity for chiral interactions. This is because the human body is composed of enzymes and receptors that are protein in nature. These proteins are polymers of 20 or so naturally occurring amino acids. With the exception of glycine, all of these amino acids are chiral (all are L-series amino acids - see later) and it must be expected that a chiral drug will interact with these chiral receptors differently from its enantiomer. It is often the case that if a racemic mixture of a chiral drug is administered, only one enantiomer will be active, while the other will be... 

There are 20 different naturally occurring amino acid residues, and each position in a biosynthesized protein-based polymer can contain any one of the 20 amino acids. As considered in Chapter 4, this means even for a small 100 residue protein-based polymer that there are (20) = 10 different sequences possible. The size of this number is hard to comprehend. For example, if the mass of the known universe were composed of nothing but 100 residue protein-based polymers and if there were only one molecule of each possible... 

Proteins are naturally occurring polymers composed of amino acid units joined one to another by amide (or peptide) bonds. 

Proteins are polymers formed from peptides in condensation reactions. Condensation of two amino acids means that the OH group of carboxyl of one peptide and a hydrogen of the amino group of the other expel a water molecule and form a peptide bond (Figure 9.4). Further condensation reactions lead to the protein. The sequence of peptides is referred to as the primary structure of the protein. The 20 amino adds composing natural proteins are given in Table 9.3. 

Proteins, polysaccharides, natural rubber, and gums are all natural polymers. The repeat units in proteins are amino acids. Nucleic acids are composed of nucleotides and polysaccharides consist of sugar units. 

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