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Describe the Chemistry of Two Types of Enzymes and Explain How the Apoenzyme Forms

Describe the Chemistry of Two Types of Enzymes and Explain How the Apoenzyme Forms


Enzymes are highly effective and narrowly focused catalyst proteins that only react with one or a small number of substrate types in biochemical reactions. They are the catalysts for nearly all chemical reactions in living organisms.

Enzymes come in two varieties: those that help combine particular molecules to produce new molecules and those that help separate particular molecules into distinct molecules. Enzymes also have a variety of significant roles outside the cell. The digestive system is one of the best illustrations of this.

The chemistry of two different types of enzymes:

Catabolic Enzymes: Enzymes that catabolize big compounds into smaller or distinct ones

Anabolic Enzymes: In order to create larger or novel molecules, anabolic enzymes can add to or connect tiny molecules.


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Lyases are enzymes that cleave C-C, C-O, C-N and other bonds by means other than by hydrolysis or oxidation. They differ from other enzymes in that two (or more) substrates are involved in one reaction direction, but there is one compound fewer in the other direction. When acting on the single substrate, a molecule is eliminated and this generates either a new double bond or a new ring. The systematic name is formed according to 'substrate group-lyase'. In common names, expressions like decarboxylase, aldolase, etc. are used. 'Dehydratase' is used for those enzymes that eliminate water. In cases where the reverse reaction is the more important, or the only one to be demonstrated, 'synthase' may be used in the name.

Ligases are enzymes that catalyze the joining of two molecules with concomitant hydrolysis of the diphosphate bond in ATP or a similar triphosphate. 'Ligase' is often used for the common name, but, in a few cases, 'synthase' or 'carboxylase' is used. 'Synthetase' may be used in place of 'synthase' for enzymes in this class.

Apoenzyme or apoprotein is an enzymatically inactive protein part of an enzyme, which requires a cofactor for its activity. Apart from catalytic RNA, most of the enzymes are proteins. Not all enzymes require a cofactor. Enzymes that do not require any cofactor are known as simple enzymes, e.g. pepsin, trypsin, etc.

A cofactor required by an apoenzyme can be a metal ion, e.g. Mg2+, Fe3+, etc., or an organic molecule called coenzyme such as NAD+, NADP+, FAD2+, etc.

Coenzymes are non-protein organic complexes, which are loosely attached to the protein part, e.g. NAD+, NADP+, etc.

The cofactor, which is tightly bound to an apoenzyme is known as a prosthetic group, e.g. heme prosthetic group attached to catalase, peroxidase, etc.

  • Simple enzymes – They are only made up of proteins, e.g. trypsin, pepsin, etc.
  • Conjugate enzymes or holoenzymes – They consist of protein as well as non-protein parts essential for the activity. The protein part of the holoenzyme is known as apoenzyme, which is inactive. The non-protein part is called a cofactor and is necessary for the catalytic function of the enzymes. E.g. metal ions (Mg2+, Fe3+, Zn2+), organic molecules or coenzymes (NAD+, NADP+, FAD2+), and prosthetic groups. E.g. catalase, alcohol dehydrogenase, pyruvate kinase, DNA polymerase, etc.

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