Define jumping genes. Classify them on the basis of their mechanism.

Jumping genes are also known as transposons. These are the nucleotide sequences of DNA that can move or displace themselves to new positions from one locus to another locus within the genome (in the same chromosome or on the different chromosome) of a single cell using transposase enzyme. Examples of transposons include IS elements in bacteria, Ac/Dc system in plants, P elements in Drosophila , Au sequence in humans. The type of jumping genes or transposons on the basis of their mechanism are: Retrotransposons: They always function with the RNA intermediate are called retrotransposons. They are translocated through a copy and paste mechanism. DNA transposons: They do not function with the RNA intermediates and are called DNA transposons. They are translocated through a copy and paste mechanism.

Sketch and label the hairpin model of tRNA.

Figure: The cloverleaf model of the tRNA The tRNA molecule contains three hairpin loops that form the shape of a three-leafed clover. One of these hairpin loops contains a sequence called the anticodon, which recognises and decodes the mRNA molecule three nucleotides (one codon) at a time during translation.

Sketch and label diagrammatic semiconservative replication of DNA.

The semiconservative mode of DNA replication was originally documented through the density labelling experiments performed by Matthew Meselson and Franklin W. Stahl. The semiconservative replication of DNA refers to a method in which, after one round of replication, every new DNA double helix would be a hybrid that consisted of one strand of old DNA bound to one strand of newly synthesised DNA. Given below is a diagrammatic representation of the replication of DNA.

Define the terms 'codon' and 'anticodon"

A codon can be characterised as a sequence of three nucleotides or triplets present on mRNA, that encodes for a specific amino acid at the time of translation. Anticodon can be best defined as a three nucleotides sequence present on tRNA, which binds to the complementary sequence present on mRNA. Anticodon sequence determines the amino acid carried by the tRNA molecule.

Enlist the histones which form an octamer of nucleosome.

The nucleosome is found in the nucleus of the eukaryotic cell. It is the basic unit of DNA packaging into chromosomes. Histones are basic in nature which helps in the packaging process of DNA. Two units of H2A, H2B, H3, and H4 histone protein form an octamer of nucleosome. That appears as a bead on a string.