An agent, such as a chemical or radiation, that could induce mutation are called mutagen. Mutations are sudden heritable changes that could be natural or artificial induced. An induced mutation is of great importance in crop improvement.

Explain briefly the process of translation in prokaryotes.

The process of translation in prokaryotes: Translation refers to the process of polymerization of amino acids to form a polypeptide or a protein. In prokaryotes, translation takes place in the cytoplasm. The order and sequence of amino acids are defined by the sequence of bases in the mRNA and the amino acids are joined by a bond which is known as a peptide bond. The formation of a peptide bond requires energy and thus, amino acids are activated in the presence of ATP and linked to their cognate tRNA by the process of charging of tRNA or aminoacylation of tRNA. If charged tRNA are brought close enough, a peptide bond is formed that is enhanced by the presence of a catalyst such as a ribosome. The ribosome in its inactive state exists as two subunits; a large subunit (50S) and a small subunit (30S). There are two sites in the large subunit, for subsequent amino acids to bind to and thus, become close enough to each other for the formation of a peptide bond. A translational unit in mRNA is the sequence of RNA that is flanked by the start codon (AUG) and the stop codon and codes for a polypeptide. An mRNA also has some additional sequences that are not translated and are referred to as untranslated regions (UTR). The UTRs are present at both 5'-end (before start codon) and at 3'-end (after stop codon) which are required for an efficient translation process. After activation of amino acids, translation starts with its three steps: Initiation Elongation Termination Initiation: For initiation, the 70S ribosome binds to the mRNA at the start codon (AUG) which is recognised only by the initiator tRNA. Elongation: The ribosome proceeds to the elongation phase of protein synthesis. During the elongation stage, complexes composed of an amino acid linked to tRNA, sequentially bind to the appropriate codon in mRNA by forming complementary base pairs with the tRNA anticodon. The ribosome moves from codon to codon along the mRNA. Amino acids are added one by one, translated into polypeptide sequences dictated by DNA and represented by mRNA. Termination: In the end, a release factor binds to the stop codon, terminating translation and releasing the complete polypeptide from the ribosome.

Describe the mechanism of DNA replication with a suitable diagram.

The process of DNA replication takes place as follows: It begins at a point called the origin of replication (ORI), to form a replication fork. The separated strands act as templates for the synthesis of new strands. DNA replicates in the 5' -→ 3' direction. dNTPs (deoxyribonucleoside-triose phosphates) act as substrates and also provide energy for the polymerization of nucleotides. DNA polymerase is an enzyme that assembles a new DNA strand that is complementary to the template strand. DNA polymerase continues to move along the template strand and add new nucleotides to the growing or complement any strand until the entire genome is replicated. The DNA polymerase forms one new strand (leading strand) in a continuous stretch in the 5' -→ 3' direction (continuous synthesis). The other new strand is formed in small stretches (Okazaki fragments) in the 5' -→ 3' direction (discontinuous synthesis). The Okazaki fragments are then joined together to form a new strand by an enzyme, DNA ligase. This new strand is called the lagging strand.