Transcription And Translation Flashcards
What is the initiator in Transcription?
Promoter recognition.
What is the enzyme which builds RNA in transcription?
RNA polymerase.
In which direction on the DNA double strand do promoters go?
Promoters can go in either direction on the strand, but they always go from 5 prime towards 3 prime so on the complementary strand this is in the opposite direction.
Define upstream and downstream on DNA in relation to a gene to be transcripted.
Downstream is in the same direction as the gene faces, and upstream is in the opposite direction.
What is a TATA box?
In eukaryotes this is found 30 base pairs before the sequence to be transcripted begins. It is the promoter sequence.
What is the promoter for transcription found in prokaryotes?
It is a pribnow box which is found 10 base pairs before the sequence with other regulation upstream at -35.
How do sequences a long way upstream have an impact on transcription?
DNA is a flexible molecule and so these two parts of the sequence may be very close together spacially.
In transcription, which strand of DNA is used as a template?
The opposite strand to the one which has the required sequence. This strand is called the template strand and the other the coding strand.
Name three ways in which RNA is processed following transcription.
Capping, polyadenation (tailing), splicing.
Where on an RNA molecule does capping occur?
Capping occurs at the 5’ end. A 5’ 5’ linkage is created with another nucleotide, which provides protection and plays a role in translation.
What is added to the 3’ end of an mRNA molecule for protection?
A poly-A tail is added which prevents against degradation.
What does the sequence AAUAA indicate on RNA during transcription?
This sequence is recognised by a specific endonuclease which then cleaves the sequence and stops transcription. After this point many Adenine nucleotides are added.
What is the difference between an endonuclease and an exonuclease?
An endonuclease cleaves somewhere in the middle of a polynucleotide whilst an exonuclease degrades a polynucleotide at one end or the other.
In splicing, what sections are removed?
Introns are removed leaving just the exons. This converts pre mRNA to mRNA which is then ready for translation. This is the template.
What is meant by the open reading frame?
The open reading frame is the section of the molecule just made up from exons which will be used as the template for translation.
Where does translation take place?
Translation occurs on ribosomes found on the rough Endoplasmic Recticulum.
What is meant by the triplet code?
This is the code which is used to identify amino acids. This is used because 4 possible bases in DNA must be converted to code for 20 different amino acids.
In translation, what is the role of tRNA?
tRNA is the Adaptor molecule which is required to convert a polynucleotide chain into a N-C polypeptide chain.
What does the codon AUG mean?
This is the initiation codon.
Give three examples of a termination codon for translation.
UAA, UAG, UGA.
In translation, how are amino acids activated?
Amino acids are activated when they bind to tRNA molecules.
What is an anticodon?
This is the three base pairs found on the tRNA molecule. They are the complementary to what is found on mRNA
What is the wobble position?
This is a base which doesn’t matter what it is in most cases. It is found on the 3’ base of a codon.
Name the enzyme involved in the activation of amino acids, and state what other molecules are required.
tRNA synthase. This process uses up ATP –> AMP + PPi
In translation, what substances recognise the cap at the end of mRNA?
Cap binding proteins, initiation factors, met-tRNA, GTP.
Describe elongation in translation.
The met-tRNA moves along the mRNA until it find AUG. This is then in the P position. The next aminoacyl-tRNA binds to the A position and this uses GTP –> GDP + Pi. A peptide bond (with another use of GTP) forms leaving the A site empty and P sit occupied by the chain.
Name the enzyme which is responsible for the reaction in translation which adds amino acids to the polypeptide.
Peptidyl transferase.
What happens at termination in translation?
When the stop codon is reached there is no amino acid to be added to the chain. The reaction involves water and give a tRNA-OH and the completed polypeptide chain.
Define transcription.
Transcription is the copying of DNA into RNA which occurs in the nucleus.
