RNA structure and transcription - L6

Question 1

What is the structure of RNA?

Answer 1

RNA is a single stranded polynucleotide. The nucleotides are joined by phosphodiester bonds and the nucleotides are made of a heterocyclic base (adenine, cytosine, guanine or uracil), a ribose sugar and a phosphate group.

Question 2

What are stem loop structures in RNA?

Answer 2

Stem loop structures are considered as secondary structural elements within RNA.

RNA has a 5’ end and a 3’ hydroxyl group. RNA contains intramolecular base-pairing interactions which leads to stem-loop structures compromising short stretches of base-paired nucleotides.

Question 3

When does transcription start and end?

Answer 3

Transcription is initiated at the promoter region of a gene, where the RNA polymerase binds, and is stopped at the terminator region.

Question 4

How is RNA synthesised?

Answer 4

RNA is synthesised by DNA-dependent RNA polymerases (RNAPs).

The genetic sequence information in the coding (or sense) strand is transcribed into RNA.

Question 5

What is the structure of the core RNAP of E.coli?

Answer 5

E. coli RNA polymerase is a pentomeric protein complex containing 5 subunits.

o The large B and B’ subunits are responsible for catalysis.
o The a,a subunits interact with transcription factors that up- or downregulate transcriptional activity.
o The w subunit is required for the assembly and stability of the complex.

Question 6

What are sigma factors?

Answer 6

Sigma factors enable RNA polymerase to scan along the DNA sequence and adopt conformation upon promoter binding. The double stranded DNA in the active site is melted to form a transcription bubble. A short RNA primer is formed. Sigma factor is released and the polymerase moves away from the promoter (promoter clearance) it becomes full engaged in RNA synthesis.

Question 7

How many nuclear RNA polymerases do eukaryotic cells have?

How many RNA polymerases do bacterial cell have.

Answer 7

Eukaryotic have 3.

Bacterial have 1.

Question 8

What is the role of…

1. RNA pol I
2. RNA pol II.
3. RNA pol III

Answer 8

1. RNA pol I transcribes ribosomal RNA.
2. RNA pol II transcribes protein-coding genes and some noncoding RNAs.
3. RNA pol III transcribes tRNA, 5S rRNA and other noncoding genes.

Question 9

What is the ‘TATA box’?

Answer 9

An A/T-rich region within the promoter region of many eukaryotic gene promoters.