What are the chemical subunits of enzymes and determines the three dimensional shape of an enzyme?

Answer 1

Enzymes are proteins that accelerate, or catalyze, chemical reactions. In these reactions, the molecules at the beginning of the process are called substrates and the enzyme converts these into different molecules: the products. Almost all processes in the cell need enzymes in order to occur at significant rates. Consequently, since enzymes are extremely selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways occur in that cell.

The activities of enzymes are determined by their three-dimensional structure.

Most enzymes are much larger than the substrates they act on, and only a very small portion of the enzyme (around 3–4 amino acids) is directly involved in catalysis. The region that contains these catalytic residues and binds the substrate and then carries out the reaction is known as the active site. Some enzymes also contain sites that bind cofactors, which are needed for catalysis. Some enzymes also have binding sites for small molecules, which are often direct or indirect products or substrates of the reaction catalyzed. This binding can serve to increase or decrease the enzyme's activity, providing a means for feedback regulation.

Like all proteins, enzymes are made as long, linear chains of amino acids that fold to produce a three-dimensional product. Each unique amino acid sequence produces a unique structure, which has unique properties. Individual protein chains may sometimes group together to form a protein complex. Most enzymes can be denatured—that is, unfolded and inactivated—by heating, which destroys the three-dimensional structure of the protein. Depending on the enzyme, denaturation may be reversible or irreversible.

Some enzymes do not need any additional components to show full activity. However, others require non-protein molecules to be bound for activity. Cofactors can be either inorganic (e.g., metal ions and iron-sulfur clusters) or organic compounds, (e.g., flavin and heme). Organic cofactors are usually called prosthetic groups. Tightly-bound cofactors are distinguished from coenzymes, such as NADH, since cofactors are regenerated as part of the catalytic mechanism and are not released from the active site during the reaction.

An example of an enzyme that contains a cofactor is carbonic anhydrase, and is shown in the diagram above with four zinc cofactors bound in its active sites. These tightly-bound molecules are usually found in the active site and are involved in catalysis. For example, flavin and heme cofactors are often involved in redox reactions.

Enzymes that require a cofactor but do not have one bound are called apoenzymes. An apoenzyme together with its cofactor(s) is called a holoenzyme (i.e., the active form). Most cofactors are not covalently attached to an enzyme, but are very tightly bound. However, organic prosthetic groups can be covalently bound (e.g., thiamine pyrophosphate in the enzyme pyruvate dehydrogenase).

Coenzymes are small molecules that transport chemical groups from one enzyme to another. Some of these chemicals such as riboflavin, thiamine and folic acid are vitamins, this is when these compounds cannot be made in the body and must be acquired from the diet. The chemical groups carried include the hydride ion (H+ + 2e-) carried by NAD or NADP+, the acetyl group carried by coenzyme A, formyl, methenyl or methyl groups carried by folic acid and the methyl group carried by S-adenosylmethionine.

for more:
http://en.wikipedia.org/wiki/Enzyme

Answer 2

Subunits Of Enzymes

Answer 3

Because the substrate(s) upon which the enzyme acts will interact (fit, if you will) with the 3D shape. For example, if you have a certain molecule, we'll call it BOBBY, and you want to break it in two (BOB and BY), you can do it better with an enzyme that has a pocket where BOBBY fits and can be held more stable and be acted upon, allowing the BB bond to be broken. Kinda like getting a collar on a dog. . .it's easier if you can get the dog (BOBBY) to hold still. Hope it helps.