Transcription

Question 1

primary transcript

Answer 1

the initial mRNA transcript that is transcribed from a protein coding gene from the DNA template; process uses a polymerase that joins nucleotides to form a single strand

Question 2

RNA polymerase

Answer 2

enzyme that synthesizes RNA nucleotides 5’ to 3’ using a DNA strand as a template

Question 3

what is the difference between RNA and DNA polymerases?

Answer 3

RNA polymerase has the ability to initiate synthesis whereas DNA polymerase needs a primer to begin transcription and the presence of 3’ OH

Question 4

RNA polymerase in bacteria

Answer 4

there is one RNA polymerase that transcribes all the different types of RNA in the cell

Question 5

RNA polymerase in eukaryotes

Answer 5

there are individual polymerases for rRNA, mRNA and tRNA; RNA polymerase I, II and III prod. rRNAs, mRNA and small RNAs (e.g. tRNA, 5S rRNA)

Question 6

what must RNA polymerases be able to do?

Answer 6

recognize the start point and the correct strand to transcribe; this is helped by promoters which are the site of attachment for RNA polymerases

Question 7

anatomy of a eukaryotic gene

Answer 7

1. promoter and transcribed region
2. genetic sequence is numbered from +1 for start site
3. upstream/5’ flanking region is numbered -vely from +1
4. eukaryotic genes contain introns (need to be removed, RNA needs to be modified before transport)

Question 8

introns

Answer 8

sequence of DNA that is not involved in coding for a protein

Question 9

operons

Answer 9

in prokaryotic cells, a cluster of genes under control of a promoter; they can produce a polycistronic transcript

Question 10

polycistronic

Answer 10

the coding pattern of prokaryotes, in which one mRNA may code for multiple proteins

Question 11

bacterial transcription

Answer 11

1. RNA polymerase binds to the promoter w/ a sigma factor, causing the strands to separate and transcription to occur
2. sigma factor is released and DNA re-anneals behind the transcript; translation can begin using the transcribed strand

Question 12

eukaryotic transcription

Answer 12

basic features identical to prokaryotes

however, each step has more proteins (also no operons)

Question 13

5’ capping

Answer 13

stabilizing mechanism with the addition of guanosine methylated by (S-adenosylmethionine/SAM) to the 5’ end of a eukaryotic mRNA during processing

Question 14

poly A tails

Answer 14

a posttranscriptional modification that acts as a protein binding site that protects mRNA transcript from degradation in cytosol; it catalyzes the addition of A’s (can be >200)

Question 15

removal of introns in eukaryotes

Answer 15

there is a sequence that signals the borders of the intron and a “spliceosome” recognizes, attaches and cuts it out at the borders accurately

Question 16

ribosomal subunits

Answer 16

the protein-production factories where amino acids are linked together in the proper order to produce a protein; can contain binding sites for antibiotics to shut down bacterial protein translation and kill bacteria when we are infected