Guide To Learn
The chromosomes in eukaryotes have much complex structure than prokaryotic chromosomes. The duplication of the chromosomes of eukaryotes involves not only the replication of their DNA but also the synthesis of the associated histone and non-histone chromosomal proteins. However, at the molecular level, the replication of DNA in eukaryotes is quite similar to prokaryotes regardless […]
Whether a cell has only one chromosome or has many chromosomes, the entire genome must be replicated precisely once for ssevery cell division. Initiation of DNA replication commits the cell to further division. Once replication started, it continues until the entire genome has been duplicated. The unit of DNA in which an individual act of […]
θ Replication Autoradiography of replicating DNA was obtained by John Cairns. This indicates how DNA replicates. Autoradiogram of circular chromosome grown in medium containing 3H thymidine shows the presence of ‘replication’ ‘eyes’ or ‘bubbles’. These are called ‘Θ structures’, because of their resemblance to Greek letter theta. This indicates that double-stranded DNA replicates by the progressive […]
Prokaryotic DNA Polymerases DNA polymerases are the enzymes responsible for the synthesis of DNA during replication. There are three types of prokaryotic DNA polymerases; namely, DNA polymerase I (DNA Pol-I), DNA polymerase II (DNA Pol-II) and DNA polymerase III (DNA Pol-III). DNA Pol-I It is the first known DNA polymerase, which was discovered by Arthur […]
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 […]