[FMS] MCG - molecular basis of transcription Flashcards
what is transcription?
from DNA to RNA
3 types of RNA and what they do
mRNA = encodes proteins
rRNA = structural and enzymatic component of the ribosome
tRNA = delivers amino acids to ribosome
what are the 3 types of RNA produced by? what process are they involved in?
PRODUCED by transcription
INVOLVED in translation
The polymerisation of ribonucleoside triphosphates into RNA is done by what?
The polymerization of ribonucleoside triphosphates (NTPs) into RNA is carried out by enzymes called RNA polymerases. These enzymes catalyze the formation of phosphodiester bonds between the ribonucleotides, resulting in the synthesis of an RNA molecule using a DNA template in transcription.
3 stages of prokaryotic transcription
Initiation.
Elongation.
Termination.
where is the promotor region in initiation during prokaryotic transcription?
found between TTGACA bases (-35 from transcription start site) and PRIBNOW BOX (-10 from transcription start site)
where is the pribnow box found?
found roughly 10 bases from start of transcription (hence -10)
describe the process of initiation in prokaryotic transcription
- RNA polymerase has affinity for DNA but is not sequence specific so sigma factor binds to -10 and -35 section, recruiting RNA POLYMERASE to bind to the transcription start site
- at the transcription start site the RNA POLYMERASE will unwind DNA as it moves, synthesising RNA, this happens in the TRANSCRIPTION BUBBLE NO PRIMER NEEDED
describe the process of elongation in prokaryotic transcription
Addition of nucleotides is in the 5’ → 3’ direction
mRNA has same sequence as the non-template (coding) strand of DNA.
describe the process of termination in prokaryotic transcription
2 types of transcription: rho-dependent and rho independent
REMEMBER:
Independent = hair pin loop
^ - mRNA transcript forms a stem loop, reducing binding of mRNA to DNA template.
- String of weak A-U pairings help detachment from DNA template.
dependent = stalker
^ - Rho has helicase activity, and unwinds the DNA-RNA duplex. Separating nascent RNA from the DNA.
- When RNA polymerase stalls, rho ‘catches up’ with it and releases the RNA from the transcription machinery.
Where does transcription start (which number nucleotide)?
Nucleotide 98. 10 nucleotides after the end of the -10 box.
What is the name of the region between ~nucleotides 58 and 97?
Promoter
in eukaryotes there are 3 types of RNA polymerases, what are they
RNA Pol I: rRNA
RNA Pol II: mRNA, snRNA
RNA Pol III: 5S rRNA, tRNA
RNA Pol II has a C-terminal domain (CTD) ‘tail’. Why?
The C-terminal domain (CTD) of RNA pol II recruits capping, splicing, and polyadenylation processing factors to eukaryotic mRNAs
Only fully processed mRNA can be exported from the nucleus and is made available for translation.
Prior to processing, the primary transcript is called what?
heterogeneous nuclear RNA(hnRNA) or pre-mRNA
^ that is mrna THAT HASNT UNDERGONE SPLICING
3 stages of eukaryotic transcription
capping
polyadenylation
splicing
what happens in capping for eukaryotic mRNA
7-methylguanosine cap formed at 5’ end
Guanosine base added ‘by reaction’ with GTP
Protects the transcript from degradation, and has roles in export from the nucleus and translation.
what happens in polyadenylation for eukaryotes
Multiple (50-250) adenosine (A) residues added to 3’ end of mRNA.
Protects the transcript from degradation, and has roles in export from the nucleus and translation.
what happens in eukaryotes in splicing
Complex of proteins (the spliceosome) removes introns.
when does splicing and capping happen?
often happens whilst transcription is ongoing – is co-transcriptional
1) Which of these statements is false?
a) Both eukaryotic and prokaryotic mRNA molecules have a 5’ UTR and a 3’ UTR.
b) Both eukaryotic and prokaryotic mRNA is synthesized in the 5’ to 3’ direction.
c) Both eukaryotic and prokaryotic mRNA contains uracil.
d) Both eukaryotic and prokaryotic mRNA is polyadenylated at the 3’ end.
D
2) In eukaryotes, mature mRNA…
a) … is capped by 7-methylguanosine at the 3’ end and polyadenylated at the 5’ end.
b) …has 7-methylguanosine attached by a 5’ to 5’ triphosphate bridge.
c) …consists of introns. The exons were removed by splicing.
d)…is exported into the nucleus after processing has finished.
B
3) Which of these statements is true?
a) Both eukaryotes and prokaryotes possess a single RNA polymerase.
b) RNA polymerase III transcribes messenger RNA in eukaryotes.
c) RNA polymerase II has a C-terminal domain tail which recruits capping, splicing and polyadenylation factors.
d) In eukaryotes, RNA polymerase II synthesizes mRNA in the 3’ to 5’ direction.
C
Explanation:
a) This statement is false. Prokaryotes typically possess a single RNA polymerase enzyme, while eukaryotes have multiple RNA polymerase enzymes (RNA polymerase I, II, and III).
b) This statement is false. RNA polymerase II primarily transcribes protein-coding messenger RNA (mRNA) in eukaryotes.
c) This statement is true. RNA polymerase II in eukaryotes possesses a C-terminal domain (CTD) tail, which plays a crucial role in recruiting factors involved in mRNA processing, such as capping, splicing, and polyadenylation.
d) This statement is false. RNA polymerase II synthesizes mRNA in the 5’ to 3’ direction, not in the 3’ to 5’ direction.
4) Which of these statements is incorrect?
a) Splicing is the removal of introns from pre-mRNA.
b) Splicing is a process that occurs in eukaryotes.
c) Splicing is performed by a complex of proteins called the spliceosome.
d) Splicing is the removal of introns from mature eukaryotic mRNA.
D
5) Which of these processes occurs in the cytoplasm?
a) Transcription in prokaryotes.
b) Transcription in eukaryotes.
c) Addition of a 5’ cap to eukaryotic pre-mRNA.
d) Addition of a polyA tail to eukaryotic pre-mRNA.
A
what is an intron?
regions of DNA that are NOT FOUND IN MATURE mRNA (they dont code for any amino acids in mature proteins)
remember =
Exon = Expressed
Intron = Ignored
what is an exon?
regions of DNA that are found in MATURE mRNA = expressed regions
remember =
Exon = Expressed
Intron = Ignored
What is the difference between thymine and uracil?
Thymine is methylated uracil.
What types of RNA are involved in transcription and translation?
mRNA is produced by transcription
mRNA, rRNA and tRNA are involved in the process of translation.
what occurs in the cytoplasm in eukaryotic vs prokaryotic transcription/ translation
EUKARYOTES
translation
PROKARYOTES
transcription
translation
which RNA polymerase has a tail?
only RNA polymerase II has a CDT tail (c-central domain tail)
