Can someone explained to me how does the DNA unwinds during the process of replication and transcription ?

Question

How come ,The DNA polymerase enzyme and RNA polymerase enzymes knows exactly which part of the DNA where the gene is expressed ???And how perfect of the accuracy of the DNA ligase enzyme reattaches the both polynucleotide strands in a perfect manner ?

Answer 1

an enzyme splits the DNA like a zipper, right down the middle.

and genes are made up of CODONS, which are 3-4 of the DNA bases in a row. some of the codons are signals to the start or end of the gene. for example, the enzyme would recognize GGA as a signal of the start of the gene. (just an example, probably not the real codon.)

and it always gets put back together right, because there is no other way that they could be put back together. each base has only 1 other base that it will connect to, A-T and C-G i believe. if they are not lined up right, it cannot connect.

Answer 2

There are signals that determine which genes need to be transcribed and translated in a particular cell. Depending on the function of that cell, those genes will be "turned on" and transcribed. For replication, there is also an intra-cellular signal that tells the entire cell "get ready to replicate" and a whole lot of different things happen like the nuclear envelop disappears, etc. Some of these signals are hormonal, some are intracellular proteins, steroids, or activation of the second messenger system (adenylate cyclase). Once replication or transcription is finished, the DNA repolymerizes like a zipper closing. It can and does happen occasionally that wrong base pairs connect but there is an enzyme that watches out and corrects for that.