An enzyme is what kind of organic compound

The active site possesses a unique conformation including correctly positioned bonding groups that is complementary to the structure of the substrate, so that the enzyme and substrate molecules fit together in much the same manner as a key fits into a tumbler lock. This model portrayed the enzyme as conformationally rigid and able to bond only to substrates that exactly fit the active site.

Working out the precise three-dimensional structures of numerous enzymes has enabled chemists to refine the original lock-and-key model of enzyme actions. They discovered that the binding of a substrate often leads to a large conformational change in the enzyme, as well as to changes in the structure of the substrate or substrates.

After catalysis, the enzyme resumes its original structure. Amino acid side chains in or near the binding site can then act as acid or base catalysts, provide binding sites for the transfer of functional groups from one substrate to another or aid in the rearrangement of a substrate.

The participating amino acids, which are usually widely separated in the primary sequence of the protein, are brought close together in the active site as a result of the folding and bending of the polypeptide chain or chains when the protein acquires its tertiary and quaternary structure. Binding to enzymes brings reactants close to each other and aligns them properly, which has the same effect as increasing the concentration of the reacting compounds.

Many enzymes are simple proteins consisting entirely of one or more amino acid chains. There are two types of cofactors: inorganic ions [e. Most coenzymes are vitamins or are derived from vitamins. Vitamins are organic compounds that are essential in very small trace amounts for the maintenance of normal metabolism.

They generally cannot be synthesized at adequate levels by the body and must be obtained from the diet. The absence or shortage of a vitamin may result in a vitamin-deficiency disease. In the first half of the 20th century, a major focus of biochemistry was the identification, isolation, and characterization of vitamins.

Despite accumulating evidence that people needed more than just carbohydrates, fats, and proteins in their diets for normal growth and health, it was not until the early s that research established the need for trace nutrients in the diet. Because organisms differ in their synthetic abilities, a substance that is a vitamin for one species may not be so for another. All fat-soluble vitamins contain a high proportion of hydrocarbon structural components.

There are one or two oxygen atoms present, but the compounds as a whole are nonpolar. In contrast, water-soluble vitamins contain large numbers of electronegative oxygen and nitrogen atoms, which can engage in hydrogen bonding with water. Most water-soluble vitamins act as coenzymes or are required for the synthesis of coenzymes.

The fat-soluble vitamins are important for a variety of physiological functions. One characteristic that distinguishes an enzyme from all other types of catalysts is its substrate specificity. An inorganic acid such as sulfuric acid can be used to increase the reaction rates of many different reactions, such as the hydrolysis of disaccharides, polysaccharides, lipids, and proteins, with complete impartiality. In contrast, enzymes are much more specific.

Some enzymes act on a single substrate, while other enzymes act on any of a group of related molecules containing a similar functional group or chemical bond. Finally, like phospholipids, cholesterol molecules are found in the cell membrane, where their hydrophobic and hydrophilic regions help regulate the flow of substances into and out of the cell.

You might associate proteins with muscle tissue, but in fact, proteins are critical components of all tissues and organs. A protein is an organic molecule composed of amino acids linked by peptide bonds. Proteins include the keratin in the epidermis of skin that protects underlying tissues, the collagen found in the dermis of skin, in bones, and in the meninges that cover the brain and spinal cord. While carbohydrates and lipids are composed of hydrocarbons and oxygen, all proteins also contain nitrogen N , and many contain sulfur S , in addition to carbon, hydrogen, and oxygen.

Proteins are polymers made up of nitrogen-containing monomers called amino acids. An amino acid is a molecule composed of an amino group and a carboxyl group, together with a variable side chain. Just 20 different amino acids contribute to nearly all of the thousands of different proteins important in human structure and function. Body proteins contain a unique combination of a few dozen to a few hundred of these 20 amino acid monomers.

All 20 of these amino acids share a similar structure Figure 2. All consist of a central carbon atom to which the following are bonded:. For this reason, they make excellent buffers, helping the body regulate acid—base balance. What distinguishes the 20 amino acids from one another is their variable group, which is referred to as a side chain or an R-group.

This group can vary in size and can be polar or nonpolar, giving each amino acid its unique characteristics. For example, the side chains of two amino acids—cysteine and methionine—contain sulfur. Sulfur does not readily participate in hydrogen bonds, whereas all other amino acids do. This variation influences the way that proteins containing cysteine and methionine are assembled. Amino acids join via dehydration synthesis to form protein polymers Figure 2.

The unique bond holding amino acids together is called a peptide bond. A peptide bond is a covalent bond between two amino acids that forms by dehydration synthesis. A peptide, in fact, is a very short chain of amino acids. Strands containing fewer than about amino acids are generally referred to as polypeptides rather than proteins.

When proteins are exposed to extreme heat, acids, bases, and certain other substances, proteins will denature. Denaturation is a change in the structure of a molecule through physical or chemical means.

Denatured proteins lose their functional shape and are no longer able to carry out their jobs. An everyday example of protein denaturation is the curdling of milk when acidic lemon juice is added.

The contribution of the shape of a protein to its function can hardly be exaggerated. For example, the long, slender shape of protein strands that make up muscle tissue is essential to their ability to contract shorten and relax lengthen.

As another example, bones contain long threads of a protein called collagen that acts as scaffolding upon which bone minerals are deposited. These elongated proteins, called fibrous proteins , are strong and durable and typically hydrophobic.

In contrast, globular proteins are globes or spheres that tend to be highly reactive and are hydrophilic. The hemoglobin proteins packed into red blood cells are an example see Figure 2.

Enzymes, introduced earlier as protein catalysts, are examples of this. The next section takes a closer look at the action of enzymes.

If you were trying to type a paper, and every time you hit a key on your laptop there was a delay of six or seven minutes before you got a response, you would probably get a new laptop.

In a similar way, without enzymes to catalyze chemical reactions, the human body would be nonfunctional. It functions only because enzymes function. Enzymatic reactions—chemical reactions catalyzed by enzymes—begin when substrates bind to the enzyme. A substrate is a reactant in an enzymatic reaction. This occurs on regions of the enzyme known as active sites Figure 2. Any given enzyme catalyzes just one type of chemical reaction. This characteristic, called specificity, is due to the fact that a substrate with a particular shape and electrical charge can bind only to an active site corresponding to that substrate.

Binding of a substrate produces an enzyme—substrate complex. It is likely that enzymes speed up chemical reactions in part because the enzyme—substrate complex undergoes a set of temporary and reversible changes that cause the substrates to be oriented toward each other in an optimal position to facilitate their interaction.

This promotes increased reaction speed. The enzyme then releases the product s , and resumes its original shape. The enzyme is then free to engage in the process again, and will do so as long as substrate remains. The fourth type of organic compound important to human structure and function are the nucleotides Figure 2. Proteins get broken down into individual amino acids. Complex carbohydrates are broken down into simple sugars. Some enzymes are very specific: they only act on one specific molecule.

Others are more general and act on a series of similar chemicals. The compound on which an enzyme acts is called its substrate.