DNA replication can be described as the process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules. This is an essential process because, whenever a cell divides, the two new daughter cells must contain the same genetic information, or DNA, like the parent cell.
The basis of the replication process is the fact that each strand of DNA can serve as a template for duplication. The process initiates at specific points, called origin of reapplication points, where the DNA double helix is unwound. A short segment of RNA, called a primer, is then synthesised and acts as a starting point for new DNA synthesis. The enzyme DNA polymerase next begins replicating the DNA by matching bases to the original strand. Once DNA synthesis is completed, the RNA primers are replaced with DNA. If there are any gaps between the newly synthesised DNA segments, they are sealed together with enzymes.
DNA replication is a crucial process; therefore, to ensure that mistakes, or mutations, are not introduced, the cell proofreads the newly synthesised DNA. Once the cellular DNA is replicated, the cell can divide into two daughter cells, which would have identical copies of the original DNA.
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Transcription can be explained as the process by which the genetic information contained within DNA is re-written into a messenger RNA (mRNA) with the help of RNA polymerase. This mRNA then exits the cell nucleus, where it provides the basis for the translation of DNA.
The process of transcription can be divided into 3 main stages:
The process is catalysed by the enzyme RNA polymerase. It attaches to a DNA and moves along with it until it recognises a promoter sequence, which indicates the starting point of transcription. There may be many promoter sequences in a DNA molecule. Transcription factors are proteins that control the rate of transcription and also bind to the promoter sequences with RNA polymerase.
Once bound to the promoter sequence, RNA polymerase unwinds a portion of the DNA double helix, exposing the bases on each of the two DNA strands.
One DNA strand known as the template strand is read in a 3′ to 5′ direction and so provides the template for the new mRNA molecule. The other DNA strand is termed as the coding strand because the base sequence of the new mRNA is identical to it, except for the replacement of thiamine bases with uracil.
Incoming ribonucleotides are used by RNA polymerase to form the mRNA strand. It does this using complementary base pairing (A to U, T to A, C to G and G to C). RNA polymerase then catalyses the formation of phosphodiester bonds between adjacent ribonucleotides. Bases can only be added to the 3′ (three-prime) end, so the strand elongates in a 5’ to 3’ direction.
Elongation will continue until the RNA polymerase encounters a stop sequence. At this point, transcription terminates and the RNA polymerase releases the DNA template.
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In this article, we will learn both similarities and differences between replication and transcription.
DNA replication and transcription are two complex biological processes and they have several differences between them. These differences between transcription and DNA replication are mentioned below:
1. What Are the Similarities Between Replication and Transcription?
Alongside differences, there are also some similarities between DNA replication and transcription. Both replication and transcription involve binding complementary nucleic acids to DNA, which yields a new strand of either DNA or RNA.
The processes can lead to errors if an incorrect nucleotide is incorporated. An error in either transcription or replication can cause a change in the gene. This occurs by either changing the DNA sequence in one of the daughter cells leading to transcription of the incorrect mRNA sequence or by causing the mRNA to incorporate an incorrect base pair that results in the wrong protein sequence being translated.
2. Write the Comparison Between Replication and Transcription.
Please have a look at the main part of this topic and the first question of the FAQ section.
3. What Are the Steps of DNA Replication?
The four steps of DNA replication are:
Replication fork formation
In eukaryotes, it takes place in the nucleus of the cell whilst in prokaryotes, it takes place in the cytoplasm of the cell.