Cell division is essential for an organism to grow, but when a cell divides it must replicate the DNA in its genome so that the two daughter cells have the same genetic information as their parent. DNA provides a simple mechanism for replication. In transcription, or RNA synthesis, the codons of a gene are copied into messenger RNA by RNA polymerase.
As opposed to DNA replication, transcription results in an RNA complement that includes uracil (U) in all instances where thymine (T) would have occurred in a DNA complement.
|Purpose||The purpose of replication is to conserve the entire genome for next generation.||The purpose of transcription is to make RNA copies of individual genes that the cell can use in the biochemistry.|
|Definition||DNA replication is the replication of a strand of DNA into two daughter strands, each daughter strand contains half of the original DNA double helix.||Uses the genes as templates to produce several functional forms of RNA|
|Products||One strand of DNA becomes 2 daughter strands.||mRNA, tRNA, rRNA and non-coding RNA( like microRNA)|
|Product processing||In eukaryotes complementary base pair nucleotides bond with the sense or antisense strand. Thesre are then connected with phosphodiester bonds by DNA helix to create a complete strand.||A 5’ cap is added, a 3’ poly A tail is added and introns are spliced out.|
|Base Pairing||Since there are 4 bases in 3-letter combinations, there are 64 possible codons (43 combinations).||RNA transcription follows base pairing rules. The enzyme makes the complementary strand by finding the correct base through complementary base pairing, and bonding it onto the original strand.|
|Codons||These encode the twenty standard amino acids, giving most amino acids more than one possible codon. There are also three 'stop' or 'nonsense' codons signifying the end of the coding region; these are the UAA, UAG and UGA codons.||DNA polymerases can only extend a DNA strand in a 5′ to 3′ direction, different mechanisms are used to copy the antiparallel strands of the double helix. In this way, the base on the old strand dictates which base appears on the new strand.|
|Result||In replication, the end result is two daughter cells.||While in transcription, the end result is a RNA molecule.|
|Product||Replication is the duplication of two-strands of DNA.||Transcription is the formation of single, identical RNA from the two-stranded DNA.|
|Enzymes||The two strands are separated and then each strand's complementary DNA sequence is recreated by an enzyme called DNA polymerase.||In transcription, the codons of a gene are copied into messenger RNA by RNA polymerase.This RNA copy is then decoded by a ribosome that reads the RNA sequence by base-pairing the messenger RNA to transfer RNA, which carries amino acids.|
|Enzymes Required||DNA Helicase, DNA Polymerase.||Transcriptase (type of DNA Helicase), RNA polymerase.|
Video Explaining the Differences
The DNA replication and mRNA transcription process are explained in the following video. Notice that while explaining about DNA replication, it also touches on the process of mutation.
How DNA Replication Works
This YouTube video shows how DNA is coiled and folded for compression and also how it is replicated in an assembly line fashion by miniature biochemical machines. While that is a great video to understand the complete system and continuous process of DNA replication, the following video shows each step of the process in more detail:
The first step in DNA replication is that the DNA double helix is unwound into two single strands by an enzyme called helicase. As explained in this video, one of these strands (called the “leading strand”) is continuously replicated in the "forward" direction while the other strand (“lagging strand”) needs to be replicated in chunks in the opposite direction. Either way, the process of replicating each DNA strand involves an enzyme called primase that attaches a “primer” to the strand that marks the spot where replication should start, and another enzyme called DNA polymerase that attaches at the primer and moves along the DNA strand adding new “letters” (bases C, G, A, T) to complete the new double helix.
Because the two strands in the double helix run in opposite directions, the polymerases work differently on the two strands. On one strand — the “leading strand” — the polymerase can move continuously, leaving a trail of new double-stranded DNA behind it.
Coordination between the leading and lagging strands being replicated
It was believed that the replication of the leading and lagging strands is somehow coordinated because in the absence of such coordination, there would be stretches of single-stranded DNA that are vulnerable to damage and undesirable mutations.
But UC Davis researches have recently found that there is in fact no such coordination. Instead, they liken the process to driving on a highway in traffic. Traffic in two lanes may appear to go slower or faster at certain times during the journey but cars in either lane would reach the destination at about the same time in the end. Similarly, the DNA replication process is full of temporary stops, restarts, and overall variable speed.