Question

Microbiology

Describe the differences in Transcription and Translation between Prokaryotes and Eukaryotes?

Why are prokaryotes able to synthesize proteins faster than eukaryotic cells?

Answer 1

Ans.

• The process by which the genetic information of DNA is copied to RNA is known as transcription.
• Translation is the process where synthesis of protein takes place in living organisms.
• Both the processes, transcription and translation, are universal and occurs in prokaryotes as well as in eukaryotes.
• Although most of the aspects of both these processes are similar in both, eukaryotes and prokaryotes, but there are still some fundmental differences between these two groups.

a). Differences in transcription between  prokaryotes and eukaryotes ;

S. No.	Prokaryotic transcription	Eukaryotic transcription
1.	Transcription occurs simultaneously with translation with both the processes taking place at the same site, the cytoplasm.	Transcription does not takes place simultaneously with translation and both the processes take place at seperate sites.
2.	Initiation machinery for transcription is simple due to lack of DNA association with histone proteins.	Initiation machinery for transcription is complex due to presence of DNA association with histone proteins.
3.	Only one type of RNA polymerase enzyme is involved.	3 types of RNA polymerase (RNA polymerase 1, 2& 3) are involved.
4.	Initiation factor is not found, instead an alpha factor is responsible for the initiation of transcription.	Transcription is initiated by the initiation fcators.
5.	Promoter region always found upstream to the site of start.	Promoter region usually is found upstream to the site of start but in some cases is found downstream to the site of initiation.
6.	Generally, no post transcription modificaton of primary transcripts takes place.	Post transcriptional modification of primary transcripts occur.
7.	The process transcription can be terminated either by rho dependent or rho independent mechanisms.	Termination mechanisms of transcription is not yet fully understood.
8.	There is no poly A tailing of mRNA.	Poly A tail is added enzymatically to the mRNA without a complementary strand.
9.	Absence of introns in mRNA.	Introns are present.

b). Differences in translation between prokaryotes and eukaryotes ;

S. No.	Eukaryotic translation	Prokaryotic translation
1.	mRNA molecules contain the coding sequence only for a single polypeptide.	mRNA are polycistronic i.e. they contain several gene's coding sequences.
2.	Takes place in the cytoplasm.	Protein synthesis in prokaryotes takes place in association with transcription and is known as coupled transcription - translation.
3.	Methionine is the first amino acid entering the ribosome but is not formylated.	Formylation of methionine occurs and forms N formyl methionine.
4.	Binding of mRNA to the small ribosomal subunit through 5'cap initiates the translation in eukryotes.	Initaition of translation in prokaryotes occurs at an AUG codon followed by a special nucleotide sequence.
5.	More number of initiating factors then the prokaryotes.	Number of intiating factors is very less (3) then the eukaryotes.
6.	Ribosome of eukaryotes is larger (80S) then the prokaryotes and is made up of a large 60S and a small 40S subunits.	Ribosome of prokaryotes is smaller (70S) then the eukaryotes with a total mass of 2700 kd.
7.	AUG is almost always the initiating codon in eukaryotes.	Multiple Shine-Dalgarno sequences can be found in the prokaryotes.

• The speed of protein synthesis is faster in prokaryotes then in the eukryotes due to the simultaneous occurance of transcription and translation.
• Due to simultaneous transcription and translation of one gene in prokaryotes, their protein synthesis is faster then the eukaryotic protein synthesis process.
• Thus, at the time when translation of mRNA into proteins occur in prokaryotes, DNA is also being transcribed simultaneously.
• Protein synthesis is slower in eukaryotes as they must complete the transcription of given segment and then transport it out of nucleus so that it's translation can begin.