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Replication and transcription occur at a high frequency in cells. Replication is the process by which DNA duplicates itself during cell division. Whereas, transcription is the process by which RNA is synthesized from a DNA template.
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DNA
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DNA, or deoxyribonucleic acid is the hereditary substance in humans and almost all other animals. The DNA of nearly every cell in a person's body is identical.The DNA molecule is made up of two strands that coil around each other to form a double helix structure.
Each strand's backbone consists of sugar (deoxyribose) and phosphate groups that alternate.
The four nucleotides that makeup DNA are:
- Adenine (A)
- Cytosine (C)
- Guanine (G)
- Thymine (T)
The nucleotides join together to form chemical bonds termed base pairs, which connect the two DNA strands (A with T and G with C).The backbone nucleotide sequence acts as a set of instructions for bringing protein and RNA molecules together.
DNA is the basic unit of inheritance in all organisms, and it does more than specify the structure and function of living things.
What is Replication?
The process of replicating a DNA molecule is known as replication. Biomolecules and organelles must be replicated and distributed across the cells before a cell replicates and divides into new daughter cells through mitosis or meiosis. DNA must be copied within the nucleus in order for each new cell to receive the correct amount of chromosomes.
Multiple proteins called replication enzymes and RNA are involved in the replication process. DNA replication occurs in eukaryotic cells, such as animal and plant cells, during the S phase of interphase of the cell cycle. In organisms, the process of DNA replication is critical for cell growth, repair, and reproduction.
What is Transcription?
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The process of replicating a segment of DNA into RNA is known as transcription. Messenger RNA (mRNA) is made up of DNA segments that have been copied into RNA molecules, which can encode proteins. Non-coding RNAs (ncRNAs) are made from segments of DNA that are not transcribed into RNA molecules.
Transcription Stages
DNA transcription can be divided into three stages: initiation, elongation, and termination.
Initiation
The process of initiation starts when the enzyme RNA polymerase attaches itself to the DNA molecule and moves until it finds a promoter sequence. This DNA sequence marks the beginning of transcription, and a DNA molecule can have many promoter sequences. Transcription factors, like RNA polymerase, bind to promoter regions and determine the rate of transcription.
RNA polymerase unwinds a piece of the DNA double helix once coupled to the promoter sequence, exposing the bases on each of the two DNA strands.
Elongation
One DNA template strand is read in a 3′ to 5′ direction. Thus, the template for the new mRNA molecule is provided.
The coding strand is another DNA strand. It is called so because its base sequence is similar to that of synthesised mRNA, with the exception of the substitution of uracil for thiamine bases.
This is accomplished by utilizing complementary base pairing to catalyse the formation of phosphodiester linkages between neighbouring ribonucleotides (A to U, T to A, C to G and G to C). The strand lengthens from 5' to 3' since bases can only be inserted at the 3′ (three-prime) end.
Termination
The RNA polymerase keeps elongating until it reaches a stop sequence. At this point, transcription comes to a halt. The DNA template is then released by the RNA polymerase.
Also Read: Human Genome Project
Difference between Replication and Transcription
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Because transcription and replication share the same DNA template, the transcription and replication machinery are likely to collide frequently, resulting in transcription–replication conflicts, DNA damage, and genomic instability.
| Replication | Transcription |
|---|---|
| It is the process of making new copies of DNA. | It is the process of copying DNA and converting it to RNA. |
| The purpose of such a process is to conserve the entire genome for the next generation. | The purpose of such a process is to make RNA copies of individual genes |
| It happens during the cell cycle's S phase. | It happens during the cell cycle's G1 and G2 phases. |
| DNA Helicase, DNA Polymerase are the enzymes required. | Transcriptase (type of DNA Helicase), RNA polymerase is the enzyme required. |
| Requires RNA primer for replication to start | Does not require a primer |
| The entire genome is copied | Only certain genes are copied |
| The raw materials are dATP, dGTP, dTTP, and dCTP. | The raw materials are ATP, UTP, GTP and CTP. |
| Occurs along the strands of DNA. | Occurs along one strand of DNA. |
| Two Daughter Strands are the products. | mRNA, tRNA, rRNA and non-coding RNA( like microRNA) are the products. |
| The replicated DNA strand remains hydrogen-bonded to its template DNA strand. | The strand of transcribed RNA separates from its DNA template strand. |
| Products remain within the nucleus. | The cytoplasm receives a greater proportion of the product than the nucleus. |
| Products are not degraded. | When a product's function is completed, it degrades. |
| It entails the complete unwinding and splitting of the DNA molecule. | It entails simply unwinding and splitting of the genes that will be transcribed.. |
| It generates regular DNA molecules that don't require any further processing. | It generates a primary RNA transcript molecule, which must be processed to obtain the final shape and size. |
Things to Remember
- Each person's genetic information is encoded in DNA. It is a two-stranded molecule with a twisted appearance that gives it the double helix form.
- The biological process of producing two identical duplicates of DNA from a single original DNA molecule is known as DNA replication. All living organisms undergo DNA replication, which is the most important aspect of biological heredity.
- The process of replicating a segment of DNA into RNA is known as transcription. DNA transcription can be divided into three stages: initiation, elongation, and termination.
- The three stages of DNA transcription are initiation, elongation, and termination.
Sample Questions
Ques. What is the process of DNA Replication? [ 3 marks]
Ans.The opening of the double helix and separation of the DNA strands, priming of the template strand, and building of a new DNA segment are the three major phases in replication. The two strands of the DNA double helix uncoil at a specific location called the origin during the separation. The strands are then primed for duplication by enzymes and proteins. Finally, the assembly of the new DNA strands is coordinated by a specific enzyme called DNA polymerase. This three-stage process applies to all cells, however, particular variations within the process may occur based on the organism and cell type.
Ques. What is the main difference between transcription and translation? [ 2 marks]
Ans. Transcription is the synthesis of RNA from a DNA template where the code in the DNA is converted into a complementary RNA code. The translation is the synthesis of a protein from an mRNA template where the code in the mRNA is converted into an amino acid sequence in a protein.
Ques. What is a transcription of DNA? [ 2 marks]
Ans. The process of replicating a segment of DNA into RNA is known as transcription. Messenger RNA (mRNA) is made up of DNA segments that have been copied into RNA molecules, which can encode proteins. Non-coding RNAs (ncRNAs) are made from segments of DNA that are not transcribed into RNA molecules.
Ques. State 3 differences between replication and transcription. [ 3 marks]
Ans.
| Replication | Transcription |
|---|---|
| The purpose of such a process is to conserve the entire genome for the next generation. | The purpose of such a process is to make RNA copies of individual genes |
| It happens during the cell cycle's S phase. | It happens during the cell cycle's G1 and G2 phases. |
| DNA Helicase, DNA Polymerase are the enzymes required. | Transcriptase (type of DNA Helicase), RNA polymerase is the enzyme required. |
Ques. What is transcription's final product? What are the promoter sequences? [ 2 marks]
Ans. The end result of transcription is an RNA transcript. It may make any type of RNA, including rRNA, mRNA, non-coding RNA, and transfer RNA (tRNA). Eukaryotes make monocistronic mRNA, whereas prokaryotes yield polycistronic mRNA.
The gene sequences that begin DNA transcription are known as promoter sequences. These are found at the 5′ end of the DNA sequence, upstream.
Ques: Explain the function of the following items in one or two lines:
(i) promoter
(ii) tRNA
(iii) Exons [ 3 marks]
Ans: Promoter: One of the three components of a transcription unit that participates in transcription is the promoter. It is found at the 5′ start of the gene and serves as a location for transcription factors (TATA Box) and RNA polymerase to connect.
tRNA is involved in the transfer of active amino acids from the cellular pool to the ribosome, where they are used to make proteins.
Exons and introns: DNA in eukaryotes is a mosaic of exons and introns. Exons are DNA coding sequences that are both transcribed and translated.
Ques. List two important functions of the ribosome during translation. [ 2 marks]
Ans. Ribosomes play two important roles during translation:
(i) they provide a surface for mRNA to bind to in the groove of the larger subunit of the ribosome.
(ii) Because the bigger subunit of the ribosome possesses peptidyl transferase on its 'P' site, it aids in the formation of peptide bonds between amino acids.
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