Write a short note on DNA ligase.

DNA ligase is an enzyme that has roles in DNA repair and DNA replication. It facilitates the joining of DNA strands together by catalysing the formation of a phosphodiester bond. This enzyme is also referred to as molecular glue, as it sticks DNA fragments together. It plays a role in repairing single-strand breaks in duplex DNA in living organisms, but some forms may specifically repair double-strand breaks. Single-strand breaks are repaired by DNA ligase using the complementary strand of the double helix as a template. DNA ligases are one of the most widely used enzymes in recombinant DNA technology to bind annealed fragments created by a restriction endonuclease.

Write a short note on RNA polymerase.

The central dogma of molecular biology has looked at RNA as a messenger molecule that exports the information coded into DNA out of the nucleus in order to drive the synthesis of proteins in the cytoplasm in eukaryotic cells. The enzyme involved in the synthesis of RNA from DNA is called RNA polymerase. RNA polymerase, also called DNA-dependent RNA polymerase, is a multisubunit enzyme that synthesises RNA from a DNA template in a process called transcription. The sequence of the RNA strand is complementary to that of the template DNA and is synthesised in a 5' → 3' orientation. The prokaryotic RNA polymerase consists of five subunits: two alpha, a beta, a small omega. This RNA polymerase transcribes all types of RNA. A eukaryotic cell contains three distinct nuclear RNA polymerases that transcribe different classes of RNA.

Draw diagrams of any two nucleotides of DNA.

A nucleotide is the structural unit of nucleic acid, i.e. both DNA or RNA. A nucleotide contains nucleoside and phosphate. A nucleoside is pentose sugar with a nitrogenous base. A nitrogenous base can be adenine, guanine, cytosine, thymine or uracil. DNA and RNA function as genetic material, and they consist of nucleotides only. Given below are diagrams of any two nucleotides of DNA.