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If it doesn't, try opening this guide in a different browser and printing from there sometimes Internet Explorer works better, sometimes Chrome, sometimes Firefox, etc. Inthe Nobel Prize in Chemistry was awarded to Frederick Sanger for his discoveries concerning the structure of proteins and, in particular, the structure of insulin. What is so important about insulin that two Nobel Prizes have been awarded for work on this protein?

Insulin is a hormone that is synthesized in the pancreas. For more information about hormones, see Chapter 7 "Lipids", Section 7. Insulin stimulates the transport of glucose into cells throughout the body and the storage of glucose as glycogen.

People with diabetes do not produce insulin or use it properly. The isolation of insulin in led to the first effective treatment for these individuals.

Proteins may be defined as compounds of high molar mass consisting largely or entirely of chains of amino acids. Their masses range from several thousand to several million daltons Da. In addition to carbon, hydrogen, and oxygen atoms, all proteins contain nitrogen and sulfur atoms, and many also contain phosphorus atoms and traces of other elements.

Proteins serve a variety of roles in living organisms and are often classified by these biological roles, which are summarized in Table 8. Muscle tissue is largely protein, as are skin and hair. Proteins are present in the blood, in the brain, and even in tooth enamel.

Each type of cell in our bodies makes its own specialized proteins, as well as proteins common to all or most cells. The dalton is a unit of mass used by biochemists and biologists.

It is equivalent to the atomic mass unit. A 30, Da protein has a molar mass of 30, u. Table 8. We begin our study of proteins by looking at the properties and reactions of amino acids, which is followed by a discussion of how amino acids link covalently to form peptides and proteins.

We end the chapter with a discussion of enzymes—the proteins that act as catalysts in the body. The proteins in all living species, from bacteria to humans, are constructed from the same set of 20 amino acidsso called because each contains an amino group attached to a carboxylic acid.

Humans can synthesize only about half of the needed amino acids; the remainder must be obtained from the diet and are known as essential amino acids. Two more amino acids have been found in limited quantities in proteins.We've updated our Privacy Policy to make it clearer how we use your personal data. We use cookies to provide you with a better experience, read our Cookie Policy. Amino acids are the building blocks that form polypeptides and ultimately proteins.

Consequently, they are fundamental components of our bodies and vital for physiological functions such as protein synthesis, tissue repair and nutrient absorption. Here we take a closer look at amino acid properties, how they are used in the body and where they come from. There are 20 amino acids that make up proteins and all have the same basic structure, differing only in the R-group or side chain they have. The simplest, and smallest, amino acid is glycine for which the R-group is a hydrogen H.

They can be subdivided according to their properties, dictated by the functional groups they possess. Broadly they are divided by chargehydrophobicity and polarity. These properties influence the way they interact with surrounding amino acids in polypeptides and proteins, and consequently impact protein 3D structure and properties.

This chart shows the chemical structures of the 20 amino acids that make up proteins. This table shows the abbreviations and single letter codes used for the 20 amino acids found in proteins.

In addition, pyrrolysine, used in the biosynthesis of proteins in some archaea and bacteria but not present in humans, and selenocysteine, a cysteine analogue only found in some lineages, are included in blue.

Finally, abbreviations used for amino acid residues with more than one potential identity, and the termination codon are shown in red to complete the alphabet of single letter abbreviations. Aspartic acid or Asparagine. Glutamic acid or Glutamine. Leucine or Isoleucine. Termination codon. Its low reactivity contributes to the simple, elongated structure of silk with few cross-links which gives the fibers strength, stretch resistance and flexibility.

Only the l-stereoisomer participates in the biosynthesis of proteins. In humans, arginine is produced when proteins are digested. It can then be converted into nitric oxide by the human body, a chemical known to relax blood vessels.

Due to its vasodilatory effects, arginine has been put forward for the treatment of people with chronic heart failure, high cholesterol, compromised circulation and high blood pressure, although research on these fronts is still ongoing. Arginine can also be produced synthetically, and arginine-related compounds can be used in treating people with liver dysfunction due to its role in promoting liver regeneration.

Although arginine is necessary for growth but not body maintenance, research has indicated that arginine is crucial to the wound-healing process, particularly in those with poor circulation.

Inasparagine was purified from asparagus juice, making it the first amino acid to be isolated from a natural source. Only the l-stereoisomer participates in the biosynthesis of mammalian proteins. Asparagine is important in the removal of toxic ammonia from the body.Each amino acid has at least one amine and one acid functional group as the name implies.

The different properties result from variations in the structures of different R groups. The R group is often referred to as the amino acid side chain. Amino acids have special common names, however, a three letter abbreviation for the name is used most of the time. A second abbreviationsingle letter, is used in long protein structures.

Consult the table on the left for structure, names, and abbreviations of 20 amino acids. There are basically four different classes of amino acids determined by different side chains: 1 non-polar and neutral, 2 polar and neutral, 3 acidic and polar, 4 basic and polar. The greater the electronegativity difference between atoms in a bond, the more polar the bond. Partial negative charges are found on the most electronegative atoms, the others are partially positive.

Review the polarity of functional groups. Side chains which have pure hydrocarbon alkyl groups alkane branches or aromatic benzene rings are non-polar. Examples include valine, alanine, leucine, isoleucine, phenylalanine. The number of alkyl groups also influences the polarity. The more alkyl groups present, the more non-polar the amino acid will be.

This effect makes valine more non-polar than alanine; leucine is more non-polar than valine. Rank the following according to increasing non-polarity i. Side chains which have various functional groups such as acids, amides, alcohols, and amines will impart a more polar character to the amino acid. The ranking of polarity will depend on the relative ranking of polarity for various functional groups as determined in functional groups.

In addition, the number of carbon-hydrogens in the alkane or aromatic portion of the side chain should be considered along with the functional group. Example: Aspartic acid is more polar than serine because an acid functional group is more polar than an alcohol group.

Example: Serine is more polar than threonine since threonine has one more methyl group than serine. The methyl group gives a little more non-polar character to threonine. Example: Serine is more polar than tyrosine, since tyrosine has the hydrocarbon benzene ring.Although there are hundreds of amino acids found in nature, proteins are constructed from a set of 20 amino acids. Generally, amino acids have the following structural properties:. All amino acids have the alpha carbon bonded to a hydrogen atom, carboxyl group, and amino group.

The "R" group varies among amino acids and determines the differences between these protein monomers. The amino acid sequence of a protein is determined by the information found in the cellular genetic code. These gene codes not only determine the order of amino acids in a protein, but they also determine a protein's structure and function.

Amino acids can be classified into four general groups based on the properties of the "R" group in each amino acid. Amino acids can be polar, nonpolar, positively charged, or negatively charged. Polar amino acids have "R" groups that are hydrophilicmeaning that they seek contact with aqueous solutions. Nonpolar amino acids are the opposite hydrophobic in that they avoid contact with liquid. These interactions play a major role in protein folding and give proteins their 3-D structure.

Below is a listing of the 20 amino acids grouped by their "R" group properties. The nonpolar amino acids are hydrophobicwhile the remaining groups are hydrophilic. Nonpolar Amino Acids.

Polar Amino Acids.


While amino acids are necessary for life, not all of them can be produced naturally in the body. Of the 20 amino acids11 can be produced naturally.

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These nonessential amino acids are alanine, arginine, asparagine, aspartate, cysteine, glutamate, glutamine, glycine, proline, serine, and tyrosine. With the exception of tyrosine, nonessential amino acids are synthesized from products or intermediates of crucial metabolic pathways.

For example, alanine and aspartate are derived from substances produced during cellular respiration. Alanine is synthesized from pyruvate, a product of glycolysis. Aspartate is synthesized from oxaloacetate, an intermediate of the citric acid cycle.

Six of the nonessential amino acids arginine, cysteine, glutamine, glycine, proline, and tyrosine are considered conditionally essential as dietary supplementation may be required during the course of an illness or in children. Amino acids that can not be produced naturally are called essential amino acids.

They are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Essential amino acids must be acquired through diet. Common food sources for these amino acids include eggs, soy protein, and whitefish.

Unlike humans, plants are capable of synthesizing all 20 amino acids.Note: You are not expected to remember the detailed structures of all these amino acids, but you should be prepared to draw the structures of the two simplest members, glycine and alanine. Note: To do so, you must remember that in the S enantiomer, the carboxyl group appears at the top of the projection formula and the amino group is on the left.

This is a good point at which to review some of the principles of stereochemistry presented in Chapter 5. Be sure to make full use of molecular models when any stereochemical issues arise.

amino acid structure formula

You need not memorize this code. For example, arginine is often regarded as being nonessential. Amino acids form polymers through a nucleophilic attack by the amino group of an amino acid at the electrophilic carbonyl carbon of the carboxyl group of another amino acid. The carboxyl group of the amino acid must first be activated to provide a better leaving group than OH. We will discuss this activation by ATP later in the course. The resulting link between the amino acids is an amide link which biochemists call a peptide bond.

In this reaction, water is released. In a reverse reaction, the peptide bond can be cleaved by water hydrolysis. When two amino acids link together to form an amide link, the resulting structure is called a dipeptide. Likewise, we can have tripeptides, tetrapeptides, and other polypeptides.

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At some point, when the structure is long enough, it is called a protein. There are many different ways to represent the structure of a polypeptide or protein, each showing differing amounts of information. Figure: Different Representations of a Polypeptide Heptapeptide.

Note: above picture represents the amino acid in an unlikely protonation state with the weak acid protonated and the weak base deprotonated for simplicity in showing removal of water on peptide bond formation and the hydrolysis reaction. Proteins are polymers of twenty naturally occurring amino acids. In contrast, nucleic acids are polymers of just 4 different monomeric nucleotides. Both the sequence of a protein and its total length differentiate one protein from another. Just for an octapeptide, there are over 25 billion different possible arrangements of amino acids.

Compare this to just different oligonucleotides of 8 monomeric units 8mer. Hence the diversity of possible proteins is enormous. The amino acids are all chiral, with the exception of glycine, whose side chain is H.

amino acid structure formula

As with lipids, biochemists use the L and D nomenclature. All naturally occuring proteins from all living organisms consist of L amino acids.Amino acids are organic compounds that contain amine —NH 2 and carboxyl —COOH functional groupsalong with a side chain R group specific to each amino acid.

About naturally occurring amino acids are known though only 20 appear in the genetic code and can be classified in many ways. In the form of proteinsamino acid residues form the second-largest component water is the largest of human muscles and other tissues.

In biochemistryamino acids which have the amine group attached to the alpha- carbon atom next to the carboxyl group have particular importance. They include the 22 proteinogenic "protein-building" amino acids, [6] [7] [8] which combine into peptide chains "polypeptides" to form the building blocks of a vast array of proteins.

Twenty of the proteinogenic amino acids are encoded directly by triplet codons in the genetic code and are known as "standard" amino acids. The other two "nonstandard" or "non-canonical" are selenocysteine present in many prokaryotes as well as most eukaryotesbut not coded directly by DNAand pyrrolysine found only in some archaea and one bacterium.

Pyrrolysine and selenocysteine are encoded via variant codons; for example, selenocysteine is encoded by stop codon and SECIS element.

Codon— tRNA combinations not found in nature can also be used to "expand" the genetic code and form novel proteins known as alloproteins incorporating non-proteinogenic amino acids. Many important proteinogenic and non-proteinogenic amino acids have biological functions. For example, in the human brainglutamate standard glutamic acid and gamma-aminobutyric acid "GABA", nonstandard gamma-amino acid are, respectively, the main excitatory and inhibitory neurotransmitters.

Glycine is a biosynthetic precursor to porphyrins used in red blood cells. Carnitine is used in lipid transport.

amino acid structure formula

Nine proteinogenic amino acids are called " essential " for humans because they cannot be produced from other compounds by the human body and so must be taken in as food. Others may be conditionally essential for certain ages or medical conditions. Essential amino acids may also differ between species.

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Industrial uses include the production of drugsbiodegradable plasticsand chiral catalysts. The first few amino acids were discovered in the early 19th century.

Amino Acids

The unity of the chemical category was recognized by Wurtz inbut he gave no particular name to it. InEmil Fischer and Franz Hofmeister independently proposed that proteins are formed from many amino acids, whereby bonds are formed between the amino group of one amino acid with the carboxyl group of another, resulting in a linear structure that Fischer termed " peptide ".The formula of a general amino acid is:.

In addition to their role as protein building blocks in living organisms, amino acids are used industrially in numerous ways. The first report of the commercial production of an amino acid was in It was then that the flavouring agent monosodium glutamate MSG was prepared from a type of large seaweed.

This led to the commercial production of MSG, which is now produced using a bacterial fermentation process with starch and molasses as carbon sources.

26.3: Structures of Amino Acids

Glycinecysteineand D,L- alanine are also used as food additives, and mixtures of amino acids serve as flavour enhancers in the food industry. Amino acids are used therapeutically for nutritional and pharmaceutical purposes.

For example, treatments with single amino acids are part of the medical approach to control certain disease states. Examples include L-dihydroxyphenylalanine L-dopa for Parkinson disease ; glutamine and histidine to treat peptic ulcers ; and argininecitrulline, and ornithine to treat liver diseases. The amino acids differ from each other in the particular chemical structure of the R group. Proteins are of primary importance to the continuing functioning of life on Earth.

Proteins catalyze the vast majority of chemical reactions that occur in the cell. They provide many of the structural elements of a cell, and they help to bind cells together into tissues.

Some proteins act as contractile elements to make movement possible. Proteins, in the form of antibodiesprotect animals from disease and, in the form of interferonmount an intracellular attack against viruses that have eluded destruction by the antibodies and other immune system defenses.

Many hormones are proteins.

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This plethora of vital tasks is reflected in the incredible spectrum of known proteins that vary markedly in their overall size, shape, and charge. By the end of the 19th century, scientists appreciated that, although there exist many different kinds of proteins in nature, all proteins upon their hydrolysis yield a class of simpler compoundsthe building blocks of proteins, called amino acids.

It was one of the first amino acids to be identified, having been isolated from the protein gelatin in In the mids scientists involved in elucidating the relationship between proteins and genes agreed that 20 amino acids called standard or common amino acids were to be considered the essential building blocks of all proteins. The last of these to be discovered, threoninehad been identified in All the amino acids but glycine are chiral molecules.

That is, they exist in two optically active asymmetric forms called enantiomers that are the mirror images of each other. This property is conceptually similar to the spatial relationship of the left hand to the right hand. One enantiomer is designated d and the other l. It is important to note that the amino acids found in proteins almost always possess only the l -configuration.

This reflects the fact that the enzymes responsible for protein synthesis have evolved to utilize only the l -enantiomers. Reflecting this near universality, the prefix l is usually omitted. Some d -amino acids are found in microorganisms, particularly in the cell walls of bacteria and in several of the antibiotics. However, these are not synthesized in the ribosome. Compounds such as amino acids that can act as either an acid or a base are called amphoteric. The pKa of a group is the pH value at which the concentration of the protonated group equals that of the unprotonated group.

Thus, at physiological pH about 7—7. Any free amino acid and likewise any protein will, at some specific pH, exist in the form of a zwitterion. That is, all amino acids and all proteins, when subjected to changes in pH, pass through a state at which there is an equal number of positive and negative charges on the molecule. The pH at which this occurs is known as the isoelectric point or isoelectric pH and is denoted as pI.