Transcription

Question 1

What is the molecular definition of a gene?

Answer 1

Genes are sequences of DNA that is transcribed into RNA
Genes can be DNA or RNA
There are two types of genes when transcribed; those RNA that is translated and RNA that is not translated

Question 2

Compare RNA and DNA polymerase

Answer 2

RNA:
Ribonucleoside uses AUCG
Made 5’-3’ adding to 3’end
DNA template read from 3-5
Produces single strand RNA

DNA:
-Deoxyribonucleoside uses ATCG
Missing oxygen on 2’ end
Produces double strand DNA

**phosphodiester bonds are present in DNA/RNA

Question 3

Does RNA polymerase require a primer

Answer 3

No because it uses other enzymes to initiate the transcription process

Question 4

What are the steps for transcription

Answer 4

1. Sigma factor binds to rna polymerase and looks for initiator sequence
2. Unwinding of DNA, abortive transcription where a few RNA are synthesized and the RNA polymerase clamps down and sigma factor is released
3. Elongation
4. RNAP is released

Question 5

Where are the promotor consensus sequence

Answer 5

Typically at -10 and -35

Question 6

Why does RNA Transcript form loops

Answer 6

Because when RNA transcript leaves RNA polymerase can base pair to itself

Question 7

Terminator Sequence

Answer 7

A strong hairpin formation pulls the RNA off of the DNA so that the DNA, RNA, and RNAP all release from each other

Question 8

How are the initial modes of transcription different from its elongation mode

Answer 8

The initial mode is inefficient and occurs very slowly (abortive state) where as the elongation mode occurs rapidly

Question 9

What are the characteristics of RNA termination

Answer 9

1. Hairpin structure formed from C-G rich sequences
2. AT rich sequences following the c-g

Question 10

How do these termination signals dissociate from DNA

Answer 10

Disrupts the H-bonding between mRNA transcript and DNA

Question 11

T/F, Translation can begin before transcription is complete for both Prokaryotes and Eukaryotes

Answer 11

False only prokaryotes

Question 12

Why can’t Eukaryotes undergo translation before transcription is complete

Answer 12

Because transcription happens in the nucleus and it cannot leave the nucleus before the process is complete

Question 13

Does Eukaryotic transcription have sigma factors

Answer 13

No they have transcription proteins which facilitates similar roles helping place RNAP at promoter

Question 14

TATA BOX

Answer 14

promoter sequence that helps position RNAP II and tells it to start transcription

Question 15

How are Eukaryotic RNAP II and Bacterial RNA different structurally

Answer 15

Bacterial RNAP has 5 subunits, EUkaryotic RNAP II has 12 RNAP II has special carboxyl terminal Domain (CTD)

Question 16

Describe the initiation process of transcription

Answer 16

For initiation to begin E needs general transcription to begin:
1. TATA box basically tells RNAP II to get ready for transcription
2. The TATA box is recognized by the TBP (TATA binding protein)
3. All of these factors assemble on the promoter
4. TFIIH pries apart the helix using ATP and it also helps RNA polymerase II get away from the other factors so it can be transcribing by adding phosphate groups to its 3’ tail

Question 17

Before the RNA can leave the nucleus it needs to undergo mRNA processing. What are the steps involved in this process

Answer 17

1. Adding 5’ cap (made from guanine and meth)- protect the RNA from exonucleases
2. Polyadenylation (Poly-A-tail)- made by an initial enzyme trimming the nucleotides and then a second enzyme comes and adds adenine tail
3. Splicing introns have a short sequence that identifies them as non-coding sequences that will be cut out-
   The splicing machine/lariat structure will cut the introns:
4. The adenine “branch-A” will attack the 5’ splice site
5. the exon on 3’ and 5’ get attached and the lariat is degraded
   **the 5’ intron will attach to 2’oh ribose of adenine

Question 18

3’ end processing

Answer 18

Up until now we have had pre-mRNA. In order for a mature mRNA to leave the nucleus 3’end processing where the Poly-A-binding protein and cleavage, along with the poly-a-tail complete the mature mRNA

Question 19

Why do we need cap and tail

Answer 19

Makes it more stable and prevents mRNA degradation after it leaves the nucleus