What is meant by satellite DNA?

DNA can be characterised as the heredity basic of life as it contains all the information related to the organism and found to be present in the nucleus of the cells. The DNA is present in the form of sets which includes all the different genes and this is known as the genome. Satellite DNA can be best defined as a non-coding DNA that does not encode the protein. DNA is mainly noticed in heterochromatin or the tightly packed regions of chromosomes in centromeres, telomeres.

Define DNA Replication. In which phase of cell cycle does replication occur in Eukaryotes ? Describe briefly the mechanism of DNA replication.

DNA can be characterised as Deoxyribose nucleic acid due to presence of deoxyribose sugar in it. DNA replication is usually described as a process in which it duplicates and produces two identical copies of itself. It occurs in all living organisms and is the most important process in biological inheritance. DNA carries information to pass from one generation to another. It acts as a blueprint for information carrier sources. DNA is found to be present in the nucleus of the cells in most of the living organism. Synthesis phase is the phase in which synthesis and replication of DNA takes place. It is the phase in which a cell doubles its DNA. For example, if the initial amount of DNA is denoted by 2 C, then after the S phase the amount of DNA would become 4 C. The amount of nucleic acid, i.e., DNA (genetic material doubles but the number of chromosomes remains the same. Origin of Replication : Replication begins at a particular region of DNA which is called origin of replication. It is because of the requirement of the origin of replication that a piece of DNA, if needed to be propagated during recombinant DNA procedures, requires a vector. Activation of deoxyribonucleotides: Four types of deoxyribonucleotides, namely, dAMP, dGMP, dTMP and dCMP are activated by phosphate, energy and enzyme phosphorylase into triphosphate state. Unwinding of helix: Unwinding of double helical parental molecule is brought about by enzyme helicase, which is ATP dependent. Unwinding of DNA molecules into two strands results in the formation of a Y-shaped structure, called replication fork. Formation of primer strand: A new strand is now to be synthesised opposite to the parental strands DNA polymerase l is the true replicase in E. coli, which is incapable of initiating DNA synthesis, ie it is unable to deposit the first nucleotide in a daughter strand. Elongation of new strand: The DNA dependent DNA polymerases catalysed polymerisation only in one direction, that is 5’---3’. This creates some additional complications at the replication fork. Consequently the replication is continuous on one template strand with polarity 3’--- 5’. It is now known as leading daughter strand.

What is Human genome project ? Briefly write about the salient features of Human Genome project.

The Human Genome Project was a scientific research program initiated in the year 1990. It was a megaproject that lasted for about 13 years. The Human Genome Project (HGP) was concerned with sequencing all the nucleotides (genetic mapping) present in the DNA (Deoxyribonucleic acid) of humans. The Human Genome Project was aimed to sequence the nucleotides digitally, such that the ‘set of genes’ can be stored in the database known as GenBank. The sequencing of genes has opened several opportunities in the field of molecular biology, the evolution of man, and also in the field of medicines. The Human Genome Project was a very long and huge collaborative project. It involved the genetic mapping of the humans, and the outcomes or features of this project were: The functions of genes over half of the discovered genes are still unknown. The proteins present in the genome (set of genes) are coded by only two percent of the genes. The human genome contains a repetitive sequence of the nucleotides and covers the large part of the genome. The gene contains approximately three thousand base pairs.