<u>The right order is:</u>
1. Helicase unzips DNA to separate strands.
Helicases are proteins that use the hydrolysis energy of ATP or GTP to catalyze the opening of paired nucleic acids (DNA or RNA) in double-stranded form. They have the ability to move in a nucleic acid directed way in double or single strand form and thus have a translocase activity (unhooks proteins attached to DNA).
2. Topoisomerase unwinds the coiled DNA.
Topoisomerases are enzymes that regulate the winding of DNA molecules.
These enzymes are able to cut one of the two paired DNA strands, pass a strand through the cut and religise the cut. This process adds or removes DNA supertours, an important mechanism for genome replication during cell multiplication.
3. Primase lays down short RNA strands.
Primase or DNA primase is an enzyme involved in the process of DNA replication. It is an RNA polymerase that allows the synthesis of short RNA segments that are then used as primers by replicative DNA polymerase. The majority of known DNA polymerases indeed need a primer and are only able to extend an already partially double-stranded region, by adding a nucleotide to a 3 'hydroxyl end already present. The primase, on the other hand, is capable of synthesizing a de novo RNA primer from a DNA template.
4. Polymerase synthesizes new DNA strands.
Polymerases are enzymes whose role is the synthesis of a strand of polynucleotide (DNA or RNA), most often using a complementary strand as template and nucleotide triphosphate (NTP or dNTP) as monomers. The polymerases synthesize the new strand in the 5 'to 3' direction, forming a new phosphodiester bond between the 3'-OH of the extended strand and the 5'-phosphate of the added nucleotide triphosphate. This is accompanied by the release of pyrophosphate from the hydrolysis of NTP or dNTP. When the polymerization uses a strand as a matrix, the polymerization is carried out in an antiparallel manner and relies on the formation of complementary base pairs.
5. The new strands are glued using ligase.
A ligase is an enzyme capable of creating a new covalent bond between two molecules.
There are many types of ligases depending on the type of covalent bond they catalyze (carbon-carbon bond, carbon-nitrogen bond, carbon-sulfur bond ...). They usually use the energy of an ATP molecule (or GTP) to catalyze the reaction.
Among the ligases, mention may be made of aminoacyl tRNA synthetases (which fix amino acids on the corresponding tRNAs) or DNA ligases (which assemble two pieces of DNA together).
