Transcription

Question 1

General definition of transcription

Answer 1

DNA –> RNA

Question 2

Similarities between DNA and RNA

Answer 2

-Linear polymer of 4 nucleotides
-Subunits linked by phosphodiester bonds

Question 3

Differences between RNA and DNA

Answer 3

-RNA nucleotides have ribose sugar
-RNA has uracil instead of thymine
-Usually single-stranded

Question 4

What are the three stages of transcription

Answer 4

Initiation
Elongation
Termination

Question 5

What happends during initiation

Answer 5

RNA polymerase binds to promoter region
DNA unwinds (template now available)

Question 6

Promotor sequence

Answer 6

Contains TATA box
Recognized by general transcription factors that recruit RNA polymerase

Question 7

What happens during elongation

Answer 7

Nucleotides added to mRNA strand by RNA polymerase

Question 8

What triggers elongation

Answer 8

RNA polymerase is phosphorylated, disengages from promotor sequence and travels along DNA strand

Question 9

What direction is elongation

Answer 9

5’-3’

Question 10

What happens during termination

Answer 10

Polyadenylation signal appears in RNA transcript
polyA tail added

Question 11

What are the key RNA processing steps

Answer 11

5’ cap
Removal of introns (splicing)
polyA tail

Question 12

5’ cap

Answer 12

first modification
Added as the RNA emerges from polymerase
Tells this cells it’s mRNA

Question 13

Splicing

Answer 13

Removal of introns

Question 14

How does the cell know where the introns are

Answer 14

Specific nucleotide sequences at the beginning and end
5’ site - donor
Middle - branch
3’ site - acceptor

Question 15

Steps of splicing

Answer 15

1. Adenine in the branch site attacks 5’ splice site
2. Sugar backbone at 5’ exon site is cut
3. 5’ end of intron covalently links to A in intron (forming a loop)
4. Free 5’ and 3’ ends of exons are joined
5. Loop od intron released

Question 16

Alternative splicing:

Answer 16

different mRNAs generated from same primary transcript

Question 17

How is splicing controlled (general)

Answer 17

Protein factors bind to intronic and extronic sequences
Splicing activator (SR) proteins
Splicing repressor (hnRNP) proteins

Question 18

RNA sequences that bind with splicing activator proteins are called…

Answer 18

Exonic splicing enhancer (ESE) or intronic splicing enhancer (ISE) sequences

Question 19

What do ESE and ISE do

Answer 19

Bind with splicing activator proteins and promote use of splicing sites

Question 20

RNA sequences that bind with splicing repressor proteins are called…

Answer 20

Exonic splicing silencer (ESS) or intronic splicing silencer (ISS) sequences

Question 21

What do ESS and ISS do?

Answer 21

Repressor proteins bind to the sequences and prevent use of the splicing sites

Question 22

polyA tail

Answer 22

Added to the end of the RNA after consensus RNA sequence facilitates termination

Question 23

Why are mutations a problem

Answer 23

Base pair substitutions can cause alternate donor or acceptor sites or the wrong use (repressor v activator)
Premature stop codons

Question 24

What is the signal for termination

Answer 24

polyadenylation signal