Transcription and Translation Flashcards
During transcription, what is transcribed?
Only the genes! Not all the DNA strand is used
Why do we call transcription this way?
It is called like that because we do not change the language of the information. We only transcribe one strand of DNA to other complementary nucleotides but in the form of RNA.
Is transcription used for mRNA only?
No. The process of transcription is used to transcribe all types of RNA for their specific function. We focus on mRNA because it has a big role in translation. However, tRNA is also produced during transciption except that it is made using another enzyme, RNA polymerase III.
How do we identify genes on a DNA strand?
We see a promoter sequence made of A’s and T’s (TATA box) and the sequence continues until closest to the 5’ carbon of the DNA strand to find a terminator sequence or other mechanisms in eukaryotes.
How do you determine which strand of DNA is transcribed and what it will be transcribed to?
mRNA is built from the 5’ carbon by adding nucleotides to the 3’ end. As transcription is antiparallel, transcription starts on the promoter that is closest to the 3’ end of the DNA strand and goes in the direction of the 5’ end. The transcription is complementary: A-U C-G
RNA synthesis requires RNA polymerase, an enzyme. What does it do in the process?
This enzyme unwinds the DNA double-helix to make two ss DNA molecules and it reads the DNA template that is in the correct orientation, adding RNA nucleotides that are complementary and antiparallel to it while recognizing the sequences of promoters and terminators.
In which organisms are there transcription factors? What do they do?
In eukaryotes, RNA polymerase needs the help of transcription factors to locate and attach to the promoter. In eukaryotes, RNA polymerase is blind and needs a guiding dog to accomplish its task.
What are transcription factors?
They are proteins that attach near the DNA promoter and form a transcription complex with the RNA polymerase.
Why are eukaryotic mRNAs able to last many hours whereas the ones of prokaryotes can only last a few minutes?
When transcription is complete, a 5’ cap is added to the beginning of the mRNA (made of many modified guanine nucleotides) and it helps protect it from degradation and helps the transport out of the nucleus (prokaryotes do not have a nucleus). Also, at the 3’ end a poly-A-tail is added also to help the transport. It is a chain of many A added to the 3’ end
Why can’t the pre-mRNA be used?
When DNA is transcribed, pre-mRNA is produced in eukaryotes because they have non-coding regions in their genes (not code for a protein). Some spliceosomes, complexes of ribonucleoproteins will cleave the primary script of RNA to join only the exons (coding regions) together. Thus, mRNA is finally produced.
Why would transcription be expected to be longer in eukaryotes?
Because there is an additional step of removing introns from pre-mRNA to make the final mRNAs?
What happens when pre-mRNA was freed from all the introns?
The mRNA is ready and it will be transported outside the nucleus for a small subunit of ribosome to attach to it and start the translation process in the cytoplasm.
Why would we have introns if they are to be removed?
They increase the variety of proteins that can be made by a gene because of alternative splicing and exon shuffling. Sometimes, not the same regions are considered as introns by the snRPS, which can change the length of the mRNA transcript.
How do you call the entire collection of transcripts that can be made by a gene given that different introns can be removed?
Transcriptome.
What would be the RNA sequence transcribed from the following DNA sequence?
5’GATTACA3’
5’UGUAAUC3’
order is flipped
