Tag: replication and protein synthesis

Arthur Kornberg purified and characterized DNA polymerase from E. coli cells which is encoded by the polA gene. It catalyzes phosphoryl group transfer. The 3-hydroxyl group of the nucleotide at the 3' end of the growing strand serve as nucleophile for nucleophilic attack at the $\alpha$ phosphorus of the incoming deoxynucleoside triphosphate. Inorganic pyrophosphate is released in the reaction. 

DNA ligase is a specific type of enzyme, a ligase, that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond. It plays a role in repairing single-strand breaks in duplex DNA in living organisms, but some forms may specifically repair double-strand breaks, i.e., a break in both complementary strands of DNA. Single-strand breaks are repaired by DNA ligase using the complementary strand of the double helix as a template, with DNA ligase creating the final phosphodiester bond to fully repair the DNA. DNA ligase has applications in both DNA repair and DNA replication.

DNA polymerase and ligase as well as RNA polymerase and ligase have an important role in DNA replication. DNA replication, like all biological polymerization processes, proceeds in three enzymatically catalyzed and coordinated steps : initiation, elongation and termination. All enzymes mentioned play important roles in these steps of replication.

The DNA polymerases are enzymes that create DNA molecules by assembling nucleotides, the building blocks of DNA. These enzymes are essential to DNA replication and usually work in pairs to create two identical DNA strands from a single original DNA molecule. During this process, DNA polymerase reads the existing DNA strands to create two new strands that match the existing ones. Every time a cell divides, DNA polymerase is required to help duplicate the cells DNA, so that a copy of the original DNA molecule can be passed to each of the daughter cells. In this way, genetic information is transmitted from generation to generation.

Helicases move along the double-stranded DNA and separate the strands by breaking hydrogen bonds at the expense of energy from ATP. DNA unwinding by helicases creates topological stress/supercoils in the helical DNA structure which is relieved by the action of topoisomerases. These enzymes transiently break both DNA strands of one chromosome thereby making the other chromosome to pass through the break and relieve the stress. DNA polymerase enzyme synthesizes DNA strands by adding deoxyribonucleotides to 3' end of the primer via phosphodiester bonds; it uses parental DNA as template. Hydrogen bonding between base pairs is facilitated by the presence of hydrogen bond donor (primary and secondary amine groups or hydroxyl groups) and complementary hydrogen bond acceptor (carbonyls and tertiary amines) in bases; it is not enzymatic process. The correct option is C.