Cloning vector is a small piece of DNA, taken from a virus, a plasmid or the cell of a higher organism that can be stably maintained in an organism. pUC 18 is the most popular E. coli cloning vector.

An expression vector or construct, is usually a plasmid or virus designed for gene expression in cells. The vector is used to introduce a specific gene into a target cell, and can commandeer the cell's mechanism for protein synthesis to produce the protein encoded by the gene.

Polymerase chain reaction (PCR) is a method widely used in molecular biology to make many copies of a specific DNA segment. Using PCR, a single copy (or more) of a DNA sequence is exponentially amplified to generate thousands to millions of more copies of that particular DNA segment

According to chromosome theory, proposed by Morgan and Castle (1912), the genes showing linkage are situated on the same pair of chromosome and are arranged in a linear fashion.

The group of nucleotides that specifies one amino acid is a code word or condo. The nucleotides of mRNA are arranged as a linear sequence of codons, each London consisting of three successive nitrogenous bases. Three codons UAG, UAA and UGA are the chain stop or termination codons. They do not code for any of the amino acids.

In most organisms AUG codon is the start or initiation codon, They do not code or any of the amino acids.

In most organisms AUG codon is the start or initiation codon, ie, the polypeptide chain starts either with methionine or N-formylmethionine.

Leucine - UUA, UUG, CUU, CUC, CUA, CUG


Alanine - GUC, GCC, GCA, GCG

GUU - Valine

UCA - Serine

Lysozyme is an enzyme that breaks down bacterial cell walls and provides protection against bacterial invasion in the skin, mucous membranes and many body fluids. It is found in tears, sweat and saliva.

Griffiths (1928), for the first time, reported transformation in bacteria and later on Avery, Mcleod and McCarthy (1944) studied it in detail.

Ligase is an enzyme that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond.

Primase is an enzyme which is involved in the replication process of DNA. It is a type of RNA Polymerase. It catalyzes the synthesis of a short RNA segment called a primer complementary to a ssDNA template.

Nucleases are enzymes that cut, shorten or degrade nucleic acids. Endonucleases are enzymes which are able to break internal phosphodiester bonds within a DNA molecule.

DNA polymerases are enzymes that synthesize a new strand of DNA complementary to an existing DNA or RNA template.

Plasmids are additional or extrachromosomal small rings of DNA having a few useful but non-vital genes like F-factor, R-factor or Nif gene. These are self-replicating and work as a vector in genetic engineering.

In unicellular organisms (bacteria, Protozoa), cells divide at very fast rate but in multicellular animals the rate of cell division is regulated by the requirement of organism as a whole.