In this method transcribes genetic information to RNA from DNA. The ultimate product of this transcription is protein. The DNA is present inside the nucleus of the cells. In managing all the cellular activities within the cells with the help of coding. For the production of proteins, this DNA code is used. DNA that carries information is not directly converted to proteins, it must first be copied to RNA. The reason behind this- the information that carries in the DNA should be destroyed.
In DNA transcription, DNA is copied for the production of RNA. To produce a protein molecule the RNA transcript is used. Initiation, elongation, and termination are the three steps for the transcription of DNA. In the promoter region. In this tutorial, we will learn about transcription in depth.
The components of transcription can be described below
Promoter − The promoter is the structural component of genes. Multiple sections are present in the promoter. The sections combine a variety of transcription factors.
Structural gene − It is part of the DNA strand. It has a polarity of 3′->5′. This strand of DNA is known by various names such as master strand, template strand, antisense, or minus strand. The other strand with a polarity of 5′ is replaced during the process of transcription. Sometimes the strand that is not participating in transcription (non-template strands) is known as a plus sign or coding strand. The reason behind this is the genetic code of this strand is the same as the genetic code ie mRNA, only uracil is replaced with thymine.
Terminator − The terminator is placed in 3′ ends. The location of the terminator is the down part of the structural genes. As we know four nucleoids constitute Deoxyribonucleic acid. They are paired together to form a DNA double helix. Adenine, guanine, cytosine, and uracil are the bases present in DNA. Adenine pairs with thymine and cytosine paired with guanine. Genetic code is the nucleotide base sequence. They give direction for protein synthesis.
DNA transcription process can be described as below
Initiation − RNA polymerase is one type of enzyme that is transcribed DNA. Instruction is given by specific nucleotide sequences to RNA polymerase. They give the instructions on where to start and close or end. The RNA polymers are mind to a DNA in a specific region called as promoter region. Specific sequences are present in the promoter region DNA. These specific sequences permit RNA polymerase to bind with DNA.
Elongation − The transcription factor is an enzyme that unwinds the DNA strand. It permits RNA polymerase to transcribe a single strand of DNA to a single strand RNA polymer that is called messenger RNA. The strand that is worked as the template is known as the antisense strand in contrast which is not worked as a template is called the sense strand. RNA is also constituted of four nucleotides bases like DNA. Namely adenine, guanine, cytosine, and uracil. At the time of RNA polymerase transcribing the DNA that time guanine pairs with cytosine and adenine pairs with uracil
Termination − To reach the terminator sequence RNA polymerase progress along with the DNA. At this movement RNA polymerase free m RNA and separates from DNA.
Prokaryotes like bacteria archaea or any other single-cell organisms do not have membrane-bound nuclei and other organelles. The transcription factors do not assist in this type of transcription and occur in the cytoplasm. It is also run simultaneously with translation. Binding, initiation, elongation, and termination are the four steps of prokaryotic transcription. In this type of single-cell transcription, DNA is transcribed by the presence of only one RNA polymerase. The mRNA strand synthesizes in the presence of catalyst RNA polymerase. The link of RNA polymerase to the promoter sequence is the first step of prokaryotic transcription. The RNA strand grows from 5′ to 3′ forming a short hybrid with the DNA strand in the elongation process. The elongation of the mRNA sequence stops once the sequence of termination reaches. Two types of termination are present in prokaryotes. In this, transcription occurs along with translation.
The process of transcription in eukaryotic cells is more complex than the prokaryotic cells. This type of transcription also involves four steps ie binding, initiation, elongation, and termination. In this type, transcription takes place in the presence of transcription factors. Based on the genes there are various types of RNA polymerase molecules are there that can transcribe the DNA. The code for protein synthesis is transcribed by RNA polymerase II. RNA polymerase I transcribed gene coding for ribosomal RNA while RNA polymerase II transcribed code for transfer RNA. Some of the cell organelles like mitochondria and chloroplasts can transcribe DNA within their cell structure. Unlike prokaryotes, eukaryotic transcription is followed by transcription i.e. both are not simultaneous processes.
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In both prokaryotic and eukaryotic transcription for RNA synthesis, DNA functions as templates. RNA molecules are produced in both types of transcription. This type of transcription is facilitated by the enzyme RNA polymerase. In both prokaryotic and eukaryotic transcription, the chemical composition remains the same.
| Prokaryotic transcription | Eukaryotic transcription |
|---|---|
| Occurs in the cytoplasm | Occurs in the nucleus |
| In the cytoplasm RNA are released and proceeds | In the nucleus RNA are released and proceeds |
| Five polypeptides constitute RNA polymerase | Ten to Fifteen polypeptides constitutes polymerases |
| Transcription and translation occurs at the same time | Transcription and translation do not occur simultaneously |
| It is not complex one | It is a complex one |
| One kind of RNA polymerase is released | Three kinds of RNA polymerase is released |
| Variation is less in promoters | Variation is more in promoters |
| Post-transcriptional modifications is absence | Post-transcriptional modifications is present |
| mRNA sequence is polycistronic | mRNA sequence is monocistronic. |
The first step of gene expression is transcription followed by translation. Both prokaryotes and eukaryotes show transcription. Prokaryotic transcription occurs in the cytoplasm and involves only RNA polymerase. While in eukaryotes transcription occurs in the nucleus and involves three RNA polymerases. Post transcription modification can be seen only in eukaryotic transcription.
Q1. What are the two types of termination in prokaryotic transcription?
Ans. Factor-dependent transcription and intrinsic termination are the two types of termination in prokaryotic transcription.
Q2. What is peptide?
Ans. Peptides are short chains of amino acids. It is bonded together with each other by the presence of a peptide bond.
Q3. What is translation?
Ans. When m RNA message code is translated to protein is known as translation.
Q4. What is cytoplasm?
Ans. It is a membrane-bound semi-liquid substance where cell organelles are present.
Q5. What is the nucleus?
Ans. It is a membrane-bound organelle in that hereditary material chromosomes are present.
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