Lecture 9

Question 1

What are the steps involved in mRNA processing prior to leaving the nucleus?

Answer 1

1. It is capped
2. Introns are spliced out by spliceosomes
   a. Lariat loops are formed by introns being spliced out
3. Consensus sequences signal where mRNA synthesis needs clipped
4. Poly A tails are added by additional proteins
   “handoff” occurs at the nuclear pore to exit the nucleus

Question 2

What are the steps in capping mRNA once it reaches 25 nucleotides in length?

Answer 2

1. The 1st nucleotide is dephosphorylated
2. GMP is added in reverse linkage (5’ to 5’ instead of 5’ to 3’)
3. A methyl group is added to the guanosine
   (sometimes another methyl group gets put on the ribose of the first nucleotide)

Question 3

outline the process of RNA transcription

Answer 3

1. RNA polymerase along with transcription factors binds to promoter DNA
2. RNA polymerase creates a “transcription bubble” in template dsDNA
3. RNA polymerase adds RNA nucleotides in a complementary fashion
4. RNA sugar-phosphate backbone forms with RNA polymerase assistance
5. New RNA strand is released when the RNA-DNA helix breaks
6. Post transcriptional processing (eukaryotes only) occurs

Question 4

what molecules supply the energy necessary for RNA transcription?

Answer 4

ATP, UTP, CTP, and GTP

Question 5

What does RNA polymerase II transcribe?

Answer 5

all protein-coding genes and snoRNA genes

Question 6

define mRNA

Answer 6

messenger RNA that codes for proteins

Question 7

Define rRNA

Answer 7

ribosomal RNA’s that form the basic structure of the ribosome and catalyze protein synthesis

Question 8

Define tRNA

Answer 8

transfer RNA’s that serve as adaptors between mRNA and amino acids being arranged to form proteins during translation

Question 9

Define snoRNA

Answer 9

small nucleolar RNA’s that help to process and chemically modify rRNA’s and spliceosomal RNA’s/mRNA’s

Question 10

Define miRNA

Answer 10

microRNA’s that regulate gene expression by blocking translation of specific mRNA’s and cause their degradation; this process is also called gene silencing

Question 11

Compare eukaryotic and prokaryotic transcription in terms of # of initiations per # of proteins transcribed for

Answer 11

Prokaryotic transcription can code for several proteins after initiation, as long as those proteins are on the same mRNA while Eukaryotic only codes for 1 protein per initiation.