Transcription is the process where the genetic information on a DNA strand is transferred into an RNA strand by a series of polymerization reactions catalyzed by enzymes called DNA-dependent RNA polymerases.
- This is the first step of gene expression where the information is passed on from one structure to another.
- During transcription, RNA molecules are initiated, elongated, and terminated. The RNA formed is the non-genetic RNA.
- Transcription occurs as a prerequisite for translation and occurs when there is a need for a particular gene product at a specific time for a specific tissue.
- Only one strand of DNA, called the template strand, is replicated during transcription, and the resulting RNA strands are single-stranded messenger RNA (mRNA).
- Transcription of a gene occurs near the chromosomal site of the gene, which is usually a short segment of the chromosome.
- The overall process of transcription is a highly controlled process catalyzed and regulated by the enzyme DNA-dependent RNA polymerase.
- The first step is the recognition of specific DNA sequences termed promoter sequences that signify the beginning of the gene.
- It is then followed by the separation of two strands of DNA and replication of one of the strands by the RNA polymerase.
- The RNA polymerase in eukaryotes is different and complex than that in prokaryotes.
- The sequence formed after replication is complementary to the template sequence as the process follows the complementary base pairing rules of DNA, except the thymine is replaced by uracil.
- In prokaryotes, the overall process is regulated by proteins that function as signals or operators and terminate the process by physically blocking the RNA polymerase once the process is complete.
- In eukaryotes, various proteins termed as transcription factors are involved in the regulation of transcription.
- Besides, the post-transcriptional modification also takes place in eukaryotes where the pre-mRNA (the result of transcription) is edited by the process of splicing before the mature mRNA reaches ribosomes for translation.
- The mRNA thus produced acts as a blueprint for protein synthesis during the process of translation.
- Depending on the sequence of DNA chosen for transcription, rRNA and tRNA synthesis also occur.
- Transcription occurs in the nucleus of eukaryotes and cytoplasm of prokaryotes where the enzymes and transcriptional factors are available.
- It is inhibited by some antibiotics like rifampicin and 8-Hydroxyquinoline.
- The process can be detected by methods like RT-PCR, DNA microarray, in-situ hybridization, and northern blotting.
Read Also: DNA Transcription (RNA Synthesis)- Article, Diagrams, and Video
The translation is the process of protein synthesis where the information on RNA is expressed in the form of polypeptide chains.
- It is the second and last step of gene expression where the information encoded on the mRNA sequence results in an amino acid sequence.
- The starting point of translation is the mRNA formed from the process of transcription of a particular DNA sequence. Thus, translation follows transcription.
- Even though the information on the mRNA is utilized to produce the amino acid sequence, other forms of RNA like tRNA is also required for the process.
- Like transcription, translation is also controlled by various factors and enzymes where the most important enzyme is the aminoacetyl tRNA synthetase.
- Translation begins with the initiation step, which involves the binding of mRNA to the ribosomes, followed by the transfer and binding of activated amino acid to the tRNA.
- The second step is elongation, where two amino acids are joined by the peptide bond as the mRNA and ribosomes move with respect to one another to ensure the translation of codons successively.
- Once all the codons are translated, the resultant polypeptide sequence is dissociated from the translation complex, and the ribosomes are also released to begin another process of translation.
- Termination is followed by post-translation modification where the polypeptide needs to be folded to obtain the three-dimensional configuration. This occurs in the endoplasmic reticulum and Golgi apparatus of the cell, and thus, the polypeptide chains are moved to those organelles.
- Other modifications are chemical in nature and involve the attachment of functional groups to the peptide sequence.
- The process of translation is regulated by the binding of ribosomal subunits to the translation complex. The ribosomes function as enzymes for the regulation of various steps.
- In eukaryotes, translation occurs in the ribosomes associated with the endoplasmic reticulum whereas, in prokaryotes, it occurs in the cytoplasm.
- The translation is inhibited by antibiotics like tetracycline, chloramphenicol, streptomycin, erythromycin, anisomycin, cycloheximide, etc.
- Similarly, the process of translation can be detected by methods like western blotting, immunoblotting, enzyme assay, Protein sequencing, etc.
Read Also: Translation (Protein Synthesis)- Definition, Enzymes, and Steps
Transcription vs Translation (Table Form)
|Basis for Comparison||Transcription||Translation|
|Definition||Transcription is the process where the genetic information on a DNA strand is transferred into an RNA strand by a series of polymerization reactions catalyzed by enzymes called DNA-dependent RNA polymerases.||The translation is the process of protein synthesis where the information on RNA is expressed in the form of polypeptide chains.|
|Gene expression||Transcription is the first step in gene expression.||The translation is the second and final step of gene expression.|
|Occurs||Transcription occurs before translation.||Translation occurs after transcription.|
|Precursor||The precursor of transcription is the non-coding or antisense DNA strand.||The precursor of translation is the mRNA produced from transcription.|
|Raw material||The raw material of transcription is the four base pairs of RNA; adenine, guanine, uracil, and cytosine.||The twenty amino acids are the raw materials of translation.|
|Initiation||The recognition of specific DNA sequences termed promoter sequences initiates transcription that signifies the beginning of the gene.||The binding of mRNA initiates the translation to the ribosomes.|
|Elongation||The elongation of RNA sequences occurs by the binding of complementary base pairs to the new sequence.||The elongation of protein occurs by the binding of amino acids.|
|Product||The product of transcription is the mRNA molecule which is complementary to the DNA strand.||The product of translation is the peptide sequences encoded from the mRNA sequence.|
|Synthesis of||Transcription results in the synthesis of RNA sequences.||Translation results in the synthesis of proteins.|
|Site||Transcription occurs in the nucleus of eukaryotes and in the cytoplasm of prokaryotes, where the enzymes and regulation factors are present.||Translation occurs in the cytoplasm of prokaryotes and in the ribosomes on the endoplasmic reticulum in eukaryotes.|
|Enzymes||The major enzymes that are responsible for transcription are DNA-dependent RNA polymerase.||The major enzyme that is responsible for translation is aminoacetyl tRNA synthetase.|
|Regulation||Transcription is regulated by various transcriptional factors in eukaryotes and by operons in prokaryotes.||Translational control is mainly brought out by the binding of ribosomal units to the translation complex.|
|Post-event modifications||Post-transcriptional modifications include the editing of pre-mRNA (the result of transcription) by the process of splicing before the mature mRNA reaches ribosomes for translation||Post-translational modifications involve the folding of polypeptide chains to obtain the three-dimensional configuration.|
|Detection||The process can be detected by methods like RT-PCR, DNA microarray, in-situ hybridization, and northern blotting.||Similarly, the process of translation can be detected by methods like western blotting, immunoblotting, enzyme assay, Protein sequencing, etc.|
|Inhibition||It is inhibited by some antibiotics like rifampicin and 8-Hydroxyquinoline.||The translation is inhibited by antibiotics like tetracycline, chloramphenicol, streptomycin, erythromycin, anisomycin, cycloheximide, etc.|
References and Sources
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