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.

What are Okazaki fragments? Which enzyme participates in their joining?

Okazaki fragments are short sequences of DNA nucleotides (about 150 to 200 base pairs long in eukaryotes) synthesised discontinuously to create the lagging strand during DNA replication. Due to the one way synthesis of the enzymes called primase and DNA polymerase, which is 5’ to 3’ direction, the two unwound template strands are replicated in different ways. One strand, the leading strand, undergoes a continuous replication; however, the lagging strand cannot be created in a continuous fashion because its template strand has 5’ to 3’ directionality, which means the polymerase must work backwards from the replication fork, creating periodic breaks. The enzyme that participates in the joining of lagging strands is ligase. This enzyme binds two DNA ends by catalysing the formation of a phosphodiester bond.

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.

Which enzyme participates in the formation of DNA from DNA?

The formation of DNA from DNA is called replication. This molecular process occurs inside the nucleus of eukaryotic cells and the cytoplasm of prokaryotic cells. Many enzymes participate in the synthesis of DNA from DNA, but a crucial enzyme that catalyses the addition of nucleotides to a DNA strand is called DNA polymerase.

Comment upon human genome project.

The Human Genome Project (HGP) was an international research program designed to study, identify, and map the genes in the human genome from both a physical and a functional standpoint. Its aim was to determine the base-pair sequences in human DNA and to store this information in computer databases. The HGP was considered a megaproject because of the following reasons. Its specific goal was to sequence every base pair in the human genome. It had invested a huge amount of money in the most advanced technologies, many scientists, and a long span of time to completely sequence the human genome.