Overview of Transcription and mRNA Formation

Question 1

What are ribonucleoside triphosphates (rNTPs)?

Answer 1

Nucleotides containing ribose as its pentose component and 3 phosphase groups.

Question 2

Why is polymerization energetically favoured?

Answer 2

Because the high‐ energy bond between the alpha and beta phosphates is replaced by a LOWER ENERGY PHOSPHODIESTER BOND.

Question 3

What reaction does RNA Polymerase catalyze?

Answer 3

FORMATION OF RNA, and thus POLYMERIZATION OF INCOMING rNTPs in RNA synthesis.

Question 4

What does initiation of transcription consist of?

Answer 4

INITIATION:
Polymerase binds to the promoter sequence, locally denatures the DNA (denaturation first start with about 12-14 base pairs, thus creating a transcription bubble), and catalyzes the first phosphodiester linkage (considered complete when the first two ribonucleotides of an RNA chain are linked by a phosphodiester bond).

Question 5

What are the 3 stages of transcription?

Answer 5

INITIATION
ELONGATION
TERMINATION

Question 6

What does elongation consist of?

Answer 6

ELONGATION:
Polymerase advances 3’‐>5’ down the template strand, denaturing the DNA and polymerizing the RNA. The enzyme maintains a melted region of about 14-20 base pairs in the transcription bubble.

Question 7

What does the “elongation complex” consists of?

Answer 7

RNA POLYMERASE
NASCENT RNA
TEMPLATE DNA

Question 8

What does termination consist of?

Answer 8

TERMINATION:

Polymerase recognizes a stop site, releases the completed RNA and dissociates from DNA.

Question 9

In what direction does RNA Polymerase move in ?

Answer 9

3’ –> 5’ down the template DNA strand.

Question 10

Can multiple polymerase molecules transcribe the same template DNA strand at the same time?

Answer 10

YES

Question 11

What is called the complete RNA molecule right after transcription?

Answer 11

PRIMARY TRANSCRIPT

Question 12

What is an operon, and are they found in procaryotes or eucaryotes?

Answer 12

They are unit made up of linked genes that are thought to regulate other genes responsible for protein synthesis.

They are specific to EUCARYOTES.

Question 13

What is the name of the 5’ cap structure?

Answer 13

7-METHYLGUANYLATE

Question 14

How is 7-methylguanylate linked to the RNA strand?

Answer 14

The cap is linked to the 5’ terminal nucleotide of the RNA by a 5’-5’ linkage.

Question 15

What does RNA processing in eukaryotes involve?

Answer 15

• POLYADENYLATION
• INTRON EXCISION
• EXON LIGATION

Question 16

What does RNA primary transcript contain?

Answer 16

• INTRONS
• EXONS
• UNTRANSLATED REGIONS (UTRs)

Question 17

What advantage presents RNA alternative splicing?

Answer 17

It gives a bigger PROTEIN DIVERSITY for a lesser amount of necessary coding/genes.

Question 18

What advantages do operons bring?

Answer 18

They facilitates the task of initiation (one initiation versus many).

Question 19

How is mRNA capped at its 3’ end?

Answer 19

It is capped by POLYADENYLATION, which is done by the addition of 100 to 250 A residues by poly(A) polymerase