Tutorial 4: Transcription

Question 1

where are proteins synthesized

Answer 1

on ribosomes

Question 2

Describe the differences between RNA and DNA

Answer 2

• ribose vs deoxyribose sugars
• U replaces T (thymine has a methyl group attaches to the number 5 carbon, U has a H
• the 5’ end of a DNA strand is typically monophosphate and the 5’ end of an RNA molecule is typically a triphosphate
• RNA molecules are shorter and single stranded

Question 3

What is RNA polymerase

Answer 3

The enzyme that synthesizes RNA from a DNA template

Question 4

what are the steps of transcription

Answer 4

1: initiation, RNA polymerase and other proteins are attrached to the double stranded DNA and transcription begins
2: elongation, succesive nucleotides are added to the 3’ end of the growing RNA trnscript as the RNA polymerase proceeds along the template strand.
3: termination, RNA poltmerase encounteds a sequence in the template strand that causes transcription to stop and the RNA transcript to be released

Question 5

what direction is the DNA template read in

Answer 5

3’ to 5’

Question 6

where does transcription start and stop

Answer 6

it starts at a promoter and ends at a terminator

Question 7

what is a TATA box

Answer 7

a specific sequence of DNA (most commonly TATAAA) found in the promoter region of many eukaryotic and archaeal genes, acting as a key regulatory element for transcription

Question 8

how is promoter recognition mediated in bacteria

Answer 8

a sigma factor which associates with RNA polymerase and facilitates its binding to specific promoters. Once transcription is initiated the sigma factor disassociates.

Question 9

how does promoter recognition in eukaryotes happen

Answer 9

it requires the combined action of at least 6 proteins known as genral transcription factors that assemble at the promoter of a gene. one or more transcriptorial activator proteins is also needed, each of which binds to a specific DNA sequence known as a enhancer

Question 10

what often happens after transcriptorial activator proteins are bound to enhancer DNA sequences

Answer 10

they attract a mediator complex of proteins which recruit RNA polymerase complex to the promoter

Question 11

what is a primary transcript

Answer 11

the RNA that comes off the DNA strand that was read

Question 12

what is mRNA

Answer 12

messenger RNA that binds to the ribosome for direct protein synthesis

Question 13

what is the difference between mRNA in prokaryotes and eukaryotes

Answer 13

in eukaryotes the primary transcript undergoes changes, in prokaryotes, the primary transcript is the mRNA. Ribosomes start protein synthesis during transcription for prokaryotes.

Question 14

what are the three types of chemical modifications during RNA processing?

Answer 14

1: a 5’ cap it added to the 5’ end of the transcript. instead of being linked by a phospidiester bond it’s linked by a triphosphate bridge because it attaches backwards (the ribosome recongnises mRNA by the 5’ cap
2: polyadenylation. 250 A bearing riboucelotides bond to the 3’ end of the transcript. This forms a poly A tail. (Both of these ends protect the transcript)
3: exons are coding sequences that are expressed and introns are coding sequences that are not. The third type of modification is the removal of introns known as RNA splicing which is done by a spliceosome

Question 15

What do introns make possible in terms of mRNA

Answer 15

Alternative splicing where primary transcripts from the same gene can be spliced into different ways to yield different mRNAs and therefore different protein products.

Question 16

What are the three (5ish)types of RNA what are not processed into mRNA and undergo their own form of processing

Answer 16

-Ribosomal RNA (rRNA)
- Transfer RNA (tRNA)
-Small nuclear RNA (smRNA) this is a component of the splicosome
- small regulatory RNA also microRNA (miRNA) and small interfering RNA (siRNA) which play a role in gene regulation