What is the function of DNA ligase?

Genetic engineering became possible with the discovery of mainly two types of enzymes i.e. the cutting enzymes or molecular scissors called restriction endonucleases and the joining enzymes called ligases. DNA ligase is the enzyme that joins a 5′ end of DNA with a 3′ end of the same or of another strand. It facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond. It is used in gene cloning to join DNA molecules together to form recombinant DNA.

Diagrammatically express the Watson Crick's semiconservative models of DNA replication.

The property of DNA double helix which led Watson and Crick to hypothesise semi-conservative mode of DNA replication is that the two strands of DNA are antiparallel and complementary to each other in terms of their base sequences. This arrangement suggests that DNA replication is semiconservative. During replication, the two strands unwind and each strand acts as a template for the synthesis of a new strand. At the end of replication, DNA of parental types and recombinant types are formed. Hence, each daughter strand has half of the DNA from the original strand and half newly-formed DNA. The diagram has been given below:

What are the two basic amino acids which are found in high amounts in histone protein?

In eukaryotes, the DNA packing is carried out with the help of positively charged histones. DNA molecules are wrapped around the alkaline histone. Histones consist of two basic amino acids arginine and lysine. Both the amino acid residue carry positive charges in their side chains. Histones and DNA are organised to form nucleosomes.

What are Okazaki fragments?

Okazaki fragments are short sequences of DNA nucleotides that are synthesised discontinuously and later linked together by the enzyme DNA ligase to create the lagging strand during DNA replication. These fragments are bound by DNA ligase, which forms a new strand of DNA. This is used as a building block for the synthesis of DNA in the lagging strand, on the template strand, the polymerase will synthesise in the opposite direction from the replication fork.

Write the application of DNA fingerprinting.

DNA fingerprinting also called DNA typing and DNA profiling is a method of isolating and identifying variable elements within the base-pair sequence of DNA. The technique was developed in 1984 by British geneticist Alec Jeffreys after he noticed that certain sequences of highly variable DNA, which do not contribute to the functions of genes, are highly repeated within them. It is widely applied in identifying and detecting a person for the unique property of DNA specificity in individuals. Two applications of DNA fingerprinting are mentioned below. Establishing family relationships. Criminal investigation in the forensic laboratory.