1). Termination codons are the nucleotide triplets in the messenger RNA and they are responsible a termination of translation of proteins. There are 3 types of termination codons: amber (UAG), ochre (UAA), and opal (UGA).
2). Lac-operon is a functioning unit of DNA containing a cluster of genes which are responsible for the transport and metabolism of lactose in bacteria.These genes are: lacZ, which encodes the enzyme β-galactosidase, lacY, which encodes lactose permease and lacA, which encodes a lactose transacetylase. The lac operon in the bacterium Escherichia coli functions by a repression mechanism where in the absence of lactose an inhibitor protein (lacI) binds to regulatory sites (lacO) in the promoter and transcription can not be performed.
3). Chemical carcinogens are agents that are capable of inducing cancer in humans or animals. They can be classified into one of four groups according to their chemical nature: hey include lipid- and water-soluble compounds, inorganic and organic chemicals, highly toxic heavy metals and alkylating agents, and relatively stable polycyclic hydrocarbons, aromatic and aliphatic amines, hydroxylamines, nitrosamines, nitroso, and nitro compounds.
4). Immobilised enzyme is an enzyme that is attached, either through adsorption or crosslinking, to inert material (for example calcium alginate). Immobilised enzymes are widely used in protein purification in affinity chromatography.