Guide To Learn
According to the proposal made by Watson and Crick for DNA duplication, once DNA replication is initiated, both the old strands of the duplex serve as templates that direct the synthesis of new complementary strand. Thus, each daughter DNA retains half of the parental DNA, i.e., the replication is semi-conservative. Figure 3.3 Semi-conservative replication-Messelson and […]
The biological information stored in the DNA must be exactly replicated and transmitted to the daughter cells. There are three modes of accomplishing this task. They are conservative, dispersive and semi-conservative mode of replication (Figure 3.2). Figure 3.2 Possible modes of DNA replication
Copying of a DNA template strand into a complementary strand is a common feature of DNA replication. The polymerization of the new DNA strand is brought about by an enzyme called DNA polymerase. The building blocks added to a growing daughter strand are individual nucleotides. The substrates for DNA syn thesis are 2′-deoxyribonucleotides. […]
DNA, the molecular chip of a cell, occupies a unique place among all the biological macromolecules, because it is considered the blueprint of an organism. The nucleotide sequence of DNA carries all the necessary information for forming the primary structures of all cellular RNAs and proteins. By encoding the enzymes, DNA indirectly affects the synthesis of […]
The hereditary nature of every living organism is defined by its ‘genome’. The genome consists of a long sequence of nucleic acid that provides the information needed to construct an organism. A genome consists of the entire set of chromosomes for any particular organism. It, therefore, comprises a series of DNA molecules (one for each […]
Griffith Transformation In 1928, Frederick Griffith performed the first experiment to prove that DNA was the hereditary material. Griffith selected the bacterium that causes pneumonia, Diplococcus pneumoniae. Two strains of the bacterium namely virulent strain and avirulent strain were used for the study. Virulence required the presence of a polysaccharide capsule around the bacterium. The avirulent […]
The Chromosomal DNA The DNA molecule may be circular or linear and can be composed of 100,000–10,000,000,000 nucleotides in a long chain. Typically, eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes, although there are many exceptions to this rule. In addition, cells may […]
There are four types of RNA, each encoded by its own type of gene: Figure 1.9 Structure of a eukayotic mRNA Messenger RNA ‘The genetic information stored in the DNA, inside the nucleus, is conveyed to the ribosomes in the cytosol for the synthesis of proteins through the mRNA. Thus, the mRNA carries the genetic […]
The double-stranded structure of a DNA determines its biological function. Metabolic events involving unwinding impose great stress on the DNA because of the constraints inherent in the double helix. Molecular processes such as replication and transcription require the unwinding of the DNA double helix. While unwinding, correct topological tension in the DNA (super-helical density) should […]
Physical Properties of the DNA Size and shape The DNA molecules range in length from about 2 microns (virus) to 2.1cm (Drosophila’s largest chromosome) to 1.6—8.2 cm (human chromosome) (1 kb DNA = 103 base pairs = 0.34 × 10-6 m). Some DNA molecules are circular (E. coli chromosome, mitochondrial DNA, plasmidDNA) and some are linear (human DNA, T7 […]