Difference Between Replication And Transcription

DNA replication and transcription are two different but related processes that take place inside the cell. Both involve DNA but differ in their role. For example-in replication DNA makes a copy of itself whereas in transcription DNA forms RNA. Both processes are complex as they require a variety of enzymes and proteins. 

Where does DNA Replication Take Place in the cell? 

DNA replication takes place in the nucleus only whereas transcription takes place in the cytoplasm. So, both processes take place inside the place but at different locations. DNA replication takes place in the S phase of the cell cycle whereas transcription takes place in G1 and G2 phases.

What is DNA Replication?

DNA is a double-stranded structure present in form of a helix. It consists of two complementary strands in which nucleotides are attached (A with T, C with G). Among the two, one will be considered as lagging and the other as the leading strand. The first step in DNA replication is to unzip the ds DNA into two single strands by an enzyme called helicase. This forms a fork-like structure, called the replication fork. The enzyme primase attaches a “primer” to the strand at a point where replication begins, called the point of replication. This is the first position where the new DNA strand will begin. 

Another enzyme called DNA polymerase attaches at the primer and moves along the DNA strand adding new nucleotides (bases C, G, A, T) in the 5’ to 3’ end to complete the new double helix. The leading strand is continuously replicated in the forward direction (5’ to 3’) while the lagging strand is replicated in chunks (Okazaki fragments) in the opposite direction (3’ to 5’). 
The whole process is repeated until the formation of the new DNA strand. Once strands are formed, an enzyme exonuclease removes all the primers from both strands. After that, enzyme ligase seals the complementary nucleotides to fix their position. Now, there is one conserved DNA and one newly synthesized DNA. This is the reason, Watson and crick called it a semiconservative model.

What is DNA Transcription?

DNA transcription involves the formation of RNA from the DNA strand. DNA consists of complementary strands in which nucleotides are paired (A with the U and C with G). So, unlike DNA replication, only a segment of DNA and only one of the strands is copied into RNA. As the two strands have opposite polarity, that is, 5’ to 3’ and 3’ to 5’.  The strand that 3’ to 5’ polarity is referred as the template strand whereas the other strand which has the polarity 5’→3′ is known as the coding strand. The coding strand has the same sequence as that of RNA (except thymine at the place of uracil). 

The coding strand does not code for anything whereas the template strand does. The DNA-dependent RNA polymerase catalyzes the polymerization in the template strand only. The DNA segment where transcription starts is called a transcription unit, consisting of a promoter, structural gene, and terminator. The structural gene is flanked by the promoter and terminator in a transcription unit. The promoter is located towards the 5′ -end (upstream) of the structural gene and provides a binding site for RNA polymerase.  Typically, the terminator, which is situated downstream of the coding strand at the 3′ end, marks the conclusion of the transcription process. In either the promoter’s upstream or downstream region, additional regulatory sequences may be found.

Differences Between DNA Replication and Transcription

Transcription and DNA replication are two intricate biological processes that differ in a number of ways. The following list outlines these variations between transcription and DNA replication:

	Characteristics	DNA replication	Transcription
1.	Definition	It is the process of making new copies (replicas) of DNA.	It is the process of making RNA from DNA strands.
2.	The difference in Nucleotides	Adenine (A) pairs with thymine (T)	Adenine (A) pairs with uracil (U)
3.	Amount of DNA involved	The whole DNA of the organism gets duplicated	Only a small segment of DNA is copied into RNA.
4.	Number of DNA strands involved	Both strands are duplicated	Only one strand is used to convert DNA into RNA
5.	Significance	Responsible for the growth and division of cells.	It is a technique for controlling gene expression.
6.	Transfer of genetic information	DNA to DNA	DNA to RNA
7.	The phase of the cell cycle	S phase	G1 and G2 phases
8.	Primers	RNA primer is involved to start replication.	No primers are required.
9.	Enzymes	DNA polymerase Helicase Ligase Primase	RNA polymerase
10.	Product	Two double-stranded (ds) DNA daughter molecules.	One single-stranded (ss) RNA
11.	Raw materials	dATP, dTTP, dCTP and dGTP	ATP, GTP, CTP, and UTP
12.	Significance	DNA is preserved for future generations.	To synthesize protein
13.	End products	Two DNA strands	mRNA, rRNA, non-coding RNA, and tRNA
14.	Degradation of end products	No degradation takes place	Degradation takes place

Similarities Between Replication and Transcription

Despite huge differences, they share some similarities also. 

1. DNA template was used in both processes. 
2. Both processes take place in all types of organisms either prokaryotic or eukaryotic.
3. Both carry specific enzymes and proteins to carry out the processes.
4. Both are part of central dogma and therefore help in the formation of proteins.
5. Both are dependent upon each other for protein synthesis.

FAQs on Replication and Transcription

Question 1: What is the similarity between DNA replication and DNA transcription?

Answer:

In both DNA is used as a template.

Question 2: How DNA Replication and Transcription are interrelated?

Answer:

They are both different steps of central dogma in which DNA replication first take place then transcription comes into consideration.

Question 3: What is the role of the Coding Strand in Transcription?

Answer:

It is the non-template strand that does not take part in the process of transcription..