RNA Synthesis

Question 1

mRNA

Answer 1

-carries the information encoded int the DNA to the cytoplasm where it is translated into proteins

Question 2

tRNA

Answer 2

-serve as carries for amino acids

Question 3

rRNA

Answer 3

-major component of the protein synthesizing machinery, the ribosome

Question 4

Where is RNA synthesized?

Answer 4

• synthesized by RNA polymerase in the nucleus.
• small % of RNA is synthesized in mitochondria
• all three classes require processing of the initial product of transcription to yield a mature RNA molecule, which takes place in the nucleus

Question 5

Constitutive proteins?

Answer 5

-transcribed essentially at a constant rate all the time

Question 6

Induced proteins

Answer 6

-made only in response to some stimulus

Question 7

Promoter

Answer 7

-region upstream (in the 5’ direction) are sequences of the nucleotides (called consensus sequences), which signal RNA polymerase to bind

Question 8

Promoter region location?

Answer 8

• 10 residues upstream from the transcription start site is the TATA box
• second region at -35 rich in T and A known as -35 region

Question 9

Nus A protein

Answer 9

• for RNA polymerase to proceed out of the transcription bubble it must lose the sigma protein
• Nus A protein displaces sigma and also plays a role in efficient elongation of the nascent RNA molecule
• Nus A dissociates at the termination step

Question 10

Hairpin Loops

Answer 10

-transcribed palindromes can base pair, they form hairpin loops, which pull away from the template

Question 11

Rho independent terminators

Answer 11

• there is an adjacent poly A stretch (8-12 nucleotides) to the hairpin
• poly A-poly-U hybrid is very unstable, hence the message dissociates from the template
• NusA is a termination factor that binds to RNA polymerase after sigma factor leaves

Question 12

Rho factor

Answer 12

• rho dependent and rho independent termination sites, which differ in sequence
• Rho factor binds to the 5’ end of messages as they are being transcribed
• when a ribosome “stalls” at rho termination site, rho factor is able to “catch-up” to the RNA polymerase and termination occurs

Question 13

Alpha-amanitin

Answer 13

• toxic compound from certain poisonous mushrooms that inhibit RNA synthesis by RNA polymerase II
• shuts down protein synthesis in the liver

Question 14

TATA and CAAT box

Answer 14

Short sequences of DNA that RNA bind to

• TATA box directs RNA polymerase to the correct start site (10-25 nucleotides upstream from the initiation site for transcription
• CAAT box present around -80 is also an important part of the promoter.