Transcription Flashcards
What is the first step of transcription?
The genetic code in DNA is transcribed into RNA.
What is the second step in DNA synthesis?
The genetic code in RNA is translated into proteins.
Why is gene expression important?
It allows for selective expression of genes and the regulation of transcription controls the time, place and level of protein expression.
What key components does transcription require?
DNA template (single stranded), RNA polymerase and ribonucleoside triphosphates (rNTPs).
How does transcription in prokaryotes differ from eukaryotes?
In prokaryotes the process is a lot simpler as RNA is made up of mostly coding regions and is much smaller than in eukaryotes.
What extra processes need to occur in transcription in eukaryotes?
Splicing (removal of introns - non-coding DNA) and capping.
What do genes do in eukaryotes if they do not code for proteins?
Act as scaffolds, make up RNA that is used in translation and transcription, processing and modification and regulating gene expression.
What are prokaryotic genes made up of?
A promoter, codons for the gene and a stop codon.
What are eukaryotic genes made up of?
Introns, exons and regulatory sequences.
What is the mechanism of transcription?
Initiation where RNA polyermase binds to the promoter and opens the helix, polymerisation where chain elongation occurs in the 5’ to 3’ direction and termination where the transcription stops at the termination signal.
What occurs in transcriptional processing?
RNA capping, polyadenylation and splicing.
What is capping?
The addition of 7-methylguanosine and the 5’ end. It is added by the enzyme guanylyltransferase and protects against degradation and may also act as a recognition site for ribosomes.
What is tailing/polyadenylation?
The addition of poly(A) residues at the 3’ end (tail) of the RNA.
What is splicing?
The highly precise removal of intron sequences. It is performed by small nuclear ribonucleoproteins (snRNPs) that combine with the RNA to form the mature RNA. They recognise exon-intron boundaries and splice the exons together by transesterification reactions.
What do activators and silencers do?
They are proteins associated with a promoter that can enhance or repress gene expression.
