[FMS] MCG - molecular basis of transcription

Question 1

what is transcription?

Answer 1

from DNA to RNA

Question 2

3 types of RNA and what they do

Answer 2

mRNA = encodes proteins

rRNA = structural and enzymatic component of the ribosome

tRNA = delivers amino acids to ribosome

Question 3

what are the 3 types of RNA produced by? what process are they involved in?

Answer 3

PRODUCED by transcription

INVOLVED in translation

Question 4

The polymerisation of ribonucleoside triphosphates into RNA is done by what?

Answer 4

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.

Question 5

3 stages of prokaryotic transcription

Answer 5

Initiation.

Elongation.

Termination.

Question 6

where is the promotor region in initiation during prokaryotic transcription?

Answer 6

found between TTGACA bases (-35 from transcription start site) and PRIBNOW BOX (-10 from transcription start site)

Question 7

where is the pribnow box found?

Answer 7

found roughly 10 bases from start of transcription (hence -10)

Question 8

describe the process of initiation in prokaryotic transcription

Answer 8

1. 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
2. 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

Question 9

describe the process of elongation in prokaryotic transcription

Answer 9

Addition of nucleotides is in the 5’ → 3’ direction
mRNA has same sequence as the non-template (coding) strand of DNA.

Question 10

describe the process of termination in prokaryotic transcription

Answer 10

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.

Question 11

Where does transcription start (which number nucleotide)?

Answer 11

Nucleotide 98. 10 nucleotides after the end of the -10 box.

Question 12

What is the name of the region between ~nucleotides 58 and 97?

Answer 12

Promoter

Question 13

in eukaryotes there are 3 types of RNA polymerases, what are they

Answer 13

RNA Pol I: rRNA
RNA Pol II: mRNA, snRNA
RNA Pol III: 5S rRNA, tRNA

Question 14

RNA Pol II has a C-terminal domain (CTD) ‘tail’. Why?

Answer 14

The C-terminal domain (CTD) of RNA pol II recruits capping, splicing, and polyadenylation processing factors to eukaryotic mRNAs

Question 15

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?

Answer 15

heterogeneous nuclear RNA(hnRNA) or pre-mRNA

^ that is mrna THAT HASNT UNDERGONE SPLICING

Question 16

3 stages of eukaryotic transcription

Answer 16

capping

polyadenylation

splicing

Question 17

what happens in capping for eukaryotic mRNA

Answer 17

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.

Question 18

what happens in polyadenylation for eukaryotes

Answer 18

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.

Question 19

what happens in eukaryotes in splicing

Answer 19

Complex of proteins (the spliceosome) removes introns.

Question 20

when does splicing and capping happen?

Answer 20

often happens whilst transcription is ongoing – is co-transcriptional

Question 21

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.

Answer 21

D

Question 22

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.

Answer 22

B

Question 23

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.

Answer 23

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.

Question 24

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.

Answer 24

D

Question 25

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.

Answer 25

A

Question 26

what is an intron?

Answer 26

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

Question 27

what is an exon?

Answer 27

regions of DNA that are found in MATURE mRNA = expressed regions

remember =

Exon = Expressed

Intron = Ignored

Question 28

What is the difference between thymine and uracil?

Answer 28

Thymine is methylated uracil.

Question 29

What types of RNA are involved in transcription and translation?

Answer 29

mRNA is produced by transcription

mRNA, rRNA and tRNA are involved in the process of translation.

Question 30

what occurs in the cytoplasm in eukaryotic vs prokaryotic transcription/ translation

Answer 30

EUKARYOTES
translation

PROKARYOTES
transcription
translation

Question 31

which RNA polymerase has a tail?

Answer 31

only RNA polymerase II has a CDT tail (c-central domain tail)