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Get Answers to all your Questions
Compare the process of DNA replication and transcription in prokaryortes.
Answers (1)
Transcription and DNA replication both involve making copies of the DNA in a cell. Transcription copies the DNA into RNA, while replication makes another copy of DNA. Both processes involve the generation of a new molecule of nucleic acids, either DNA or RNA; however, the function of each process is very different, with one involved in gene expression and the other involved in cell division. Although DNA and RNA have some chemical similarities, each molecule performs different functions in living organisms.
TRANSCRIPTION
Transcription involves copying DNA into RNA. The portion of the DNA that codes for genes is transcribed, or copied, into messenger RNA, known as mRNA. The first step in the process is the unwinding and separation of the two strands of the DNA helix. RNA polymerase binds to promoter and initiates transcription (Initiation). It uses nucleoside triphosphates as substrate and polymerises in a template depended fashion following the rule of complementarity. It somehow also facilitates opening of the helix and continues elongation. Only a short stretch of RNA remains bound to the enzyme. Once the polymerases reaches the terminator region, the nascent RNA falls off, so also the RNA polymerase. This results in termination of transcription. The RNA polymerase is only capable of catalysing the process of elongation. It associates transiently with initiation-factor (σ) and termination-factor (ρ) to initiate and terminate the transcription, respectively. Association with these factors alter the specificity of the RNA polymerase to either initiate or terminate.
DNA REPLICATION
DNA replication is the process of copying the DNA in a cell so that there are two copies. This is done in preparation for cell division, or mitosis. Before a cell divides, the DNA must be copied so that there is a copy for each of the resulting daughter cells.
The main enzyme of DNA Replication is referred to as DNA-dependent DNA polymerase, since it uses a DNA template to catalyse the polymerisation of deoxynucleotides. For long DNA molecules, since the two strands of DNA cannot be separated in its entire length (due to very high energy requirement), the replication occur within a small opening of the DNA helix, referred to as replication fork. The DNA-dependent DNA polymerases catalyse polymerisation only in one direction, that is 5'--3'. This creates some additional complications at the replicating fork. Consequently, on one strand (the template with polarity 3'--5'), the replication is continuous, while on the other (the template with polarity 5'--3'), it is discontinuous. The discontinuously synthesised fragments are later joined by the enzyme DNA ligase . The DNA polymerases on their own cannot initiate the process of replication. There is a definite region in E. coli DNA where the replication originates. Such regions are termed as origin of replication.
DIFFERENCES
DNA replication occurs in preparation for cell division, while transcription happens in preparation for protein translation. DNA replication is important for properly regulating the growth and division of cells. The DNA will not replicate if the cell lacks certain growth factors, thereby keeping the cell division rate under control. Transcription of DNA is the method for regulating gene expression. Although all of our cells contain copies of all of our genes, each cell only expresses, or turns on, the genes that are necessary for the functions of that cell. Transcription only occurs when a gene is turned on.
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