Guide To Learn
Nirenberg and Khorana Experiment Marshall W. Nirenberg and Heinrich J. Matthaei (1962) made their own simple and artificial mRNA and identified the polypeptide product that was encoded by it. They used the enzyme polynucleotide phosphorylase, which randomly polymerizes any RNA nucleotides that it finds. They began with the simplest codes possible. Polynucleotide phosphorylase was added […]
Codons DNA specifies protein through an mRNA. Hidden within the mRNA lies the ‘triplet code’, a series of three nucleotides, called codons that code for a single amino acid. There are only 20 amino acids that occur in naturally derived proteins. The mRNA contains four different nucleotides namely: adenine (A), uracil (U), guanine (G) and […]
Proteins are the end products of most information pathways. A cell requires about thousands of different proteins. Translation is the process of the synthesis of proteins in the cell. Translation is a complex biosynthetic process that involves several proteins, enzymes and RNA molecules. The genetic information stored in the DNA is transcribed into a messenger […]
The discovery of reverse transcriptase has modified the central dogma of molecular biology, which held that genetic information should pass only from DNA to RNA. This enzyme synthesizes DNA from RNA, thus showing that the information can flow from RNA to DNA. The enzyme was discovered by David Baltimore and Howard M. Temin in the […]
A large variety of inhibitors of RNA synthesis have been identified. The inhibitors fall into three groups. They are: Inhibitors Acting by Binding to DNA The best-known example of inhibitors that bind to DNA is actinomycin D, an antibiotic produced by Streptomyces antiboticus. The inhibition of RNA synthesis is caused by the insertion of its […]
The immediate products of transcription, the primary transcripts, are not necessarily biologically active. In order to make them as functional entities, many of them must be altered in several ways. These modifications are referred to as post-transcriptional modifications or processing, which include: mRNA Processing Prokaryotic mRNA In prokaryotes, most primary mRNA transcript functions in translation […]
The eukaryotic transcription is more complex than the prokaryotic transcription due to the cellular compartmentalization. The genetic material in eukaryotes is primarily localized in the nucleus. A nuclear membrane separates the nucleus from the cytoplasm, where the protein synthesis takes place. The promoters for different genes are different. Each promoter contains a combination of sites […]
Eukaryotic cells contain three different RNA polymerases, designated as I, II and III, which catalyse the transcription of genes encoding different classes of RNA. The subunit structure of yeast RNA polymerase is depicted in the following (Figure 4.11). Figure 4.11 Yeast RNA polymerases and their submits RNA Polymerase-I RNA polymerase-I (RNA Pol-I) is located in […]
Binding of RNA Polymerase RNA polymerase is sufficiently large enzyme that can come into contact with many DNA bases simultaneously. An estimate of the size of the region of the DNA where contact is made is obtained by selectively degrading adjacent DNA bases with DNase, a procedure known as ‘DNase protection method’. Figure 4.7 DNA […]
All genes of the genome are not transcribed at all the time. In higher eukaryotes (such as human beings) especially, where there is a tissue-specific gene expression (such as muscle, for example), there is selective transcription of the genome. Therefore, it would be a tremendous waste of a cell’s resources to transcribe unnecessary genes. Transcription […]