In mammalian cells, including those of human beings, DNA-dependent RNA polymerase first synthesises precursor RNA in the nucleoplasm. This precursor is then degraded by a nuclear nuclease to mRNA that is then translocated to the cytoplasm, where it becomes associated to the ribosomal system. This precursor RNA constitutes the fourth class of RNA molecules and…

The abundance of RNA n the cytoplasm and its role in protein synthesis suggested that the genetic information of nuclear DNA is transmitted to an RNA which functions at the sites of protein synthesis. In 1961, the two Nobel laureates Francois Jacob and Jacques Monod postulated that control of protein formation, at least in certain…

The tertiary structure (or three-dimensional structure) of a tRNA molecule is given in Figure 5.8. Figure 5.8 Structure of tRNA Alexander Rich and Aaron Klug on the basis of their X-ray crystallographic studies have elucidated the 3-D structure of the phenylalanine-accepting tRNA from yeast as shown in Figure 5.9. The important features observed by them are the following:…

Robert W. Holley and coworkers determined the base sequence of a tRNA molecule specific for the amino acid alanine in 1965. The molecular structure of rRNA is shown in Figure 5.7. Figure 5.7 Molecular Structure of rRNA Ribosomes and their RNAs are given in Table 5.6.   Table 5.6 Ribosomes and their RNAs Ribosomes rRNA Prokaryotic ribosomes   30S60S…

Transfer RNA is the smallest polymeric form of RNA. In abundance, the tRNA comes next to rRNA and amounts to about 15% of total RNA of the cell. The tRNA molecule serves a number of functions; the most important of which is to act as specific carriers of activated amino acids to specific sites on…

It is the most stable form of RNA and is found in ribosomes. It has the highest molecular weight. In bacterium Escherichia Coli, there are three kinds of RNA called 23S, 16S, and 5S RNA because of sedimentation behaviour. One molecule of each of these three types of rRNA is present in each ribosome. Ribosomal…

In all prokaryotic and eukaryotic organisms, three general types of RNAs are found: ribosomal, transfer, and messenger RNAs. Each of these polymeric forms serves as extremely important informational links between DNA, the master carrier of information and proteins. The three types of RNA molecules differ from each other by size, function, and general stability. Table 5.5 shows…

Although many features can be shared with DNA, the RNA molecules possess several specific differences. As apparent from its name, the sugar moiety in RNA, to which the phosphate and the nitrogen bases are attached, is ribose rather than the 2′deoxyribose of DNA. Ribose contains a 2′ hydroxyl group not present in deoxyribose. RNA contains…

Ribonucleic acid (RNA), like DNA, is a long, unbranched macromolecule, consisting of nucleotides joined by 3′→ 5′ phosphodiester bond. The number of ribonucelotides RNA ranged from as few as 75 to many thousands.

A new technique called hybridisation was developed in 1961 by Sol Spiegelman. The concept lying behind this technique is that the ability of the complementary DNA strands to pair with one another can be used to detect similar DNA sequence into two different species or with genome of single species as shown in Figure 5.6. Figure…