lecture 24

Question 1

is in prokaryotes the coding region of a gene interrupted

Answer 1

In prokaryotes, the coding region of a
gene is not interrupted: the sequence of the gene is co-linear with the amino acid sequence of the protein

Question 2

what is the Shine-Dalgarno sequence

Answer 2

The Shine-Dalgarno sequence, 5’ UAAGGAGGU 3’ is
involved in the initiation of translation (covered in Chap. 15).

Question 3

what are exons and introns in eukaryotes

Answer 3

exons are protein
coding segments, introns are intervening (non-coding) segments

Question 4

what is the first step in the processing of the mRNA in the eukaryotes

Answer 4

Addition of 7-Methyl Guanosine (7-MG)
Cap

Question 5

when and how does the Addition of 7-Methyl Guanosine (7-MG) Cap happens

Answer 5

addition of 7-MG cap occurs early
in the elongation process
Linked to pre-mRNA by a unique linkage
between the 5’ phosphate of the 7-MG and
the 5’ phosphate of the first ribonucleotide
in the RNA (5’ to 5’ phosphate linkage).

Question 6

what is the process of Addition of the 3’ poly(A)
tail

Answer 6

-eukaryotic pre-mRNA is
cleaved 11-30 nt following
the 5’ AAUAAA 3’ sequence
in the pre-mRNA.
-Poly A polymerase adds a
string of ~200 A residues at
the cleaved end.

Question 7

what are the three main steps of processing in eukaryotic nuclear
pre-mRNA

Answer 7

A. Addition of 7-Methyl Guanosine (7-MG)
Cap
B. Addition of PolyA tail
C. Removal of introns

Question 8

how is the Removal of introns process

Answer 8

Removal of introns must be
precise in order to properly
fuse the 3’ end of one exon
to the 5’ end of the next exon.

Question 9

what are the two conserved
sequences that are required for its
precise removal in introns

Answer 9

A. 5’ and 3’ splice sequences containing
the junction sequences “GU and AG”,
respectively.
B. Intron Branch point: a conserved “A”
residue

Question 10

which protein help in removal of an intron

Answer 10

Removal of introns-accomplished by an RNA/protein
complex known as the “Spliceosome”

Question 11

what is a spliceosome?

Answer 11

• It’s an RNA/protein structure
• It contains five small nuclear RNAs
  (snRNAs): designated U1, U2, U4,
  U5, and U6
• The snRNAs associate with about 40
  small proteins to form small nuclear
  ribonucleoproteins (snRNPs).
  [pronounced.. “SNURPS”]
• snRNPs U1, U2, U4/U6 and U5
  assemble to form a complete
  “spliceosome”

Question 12

what is the lariat formation

Answer 12

lariat formation involves a
unique linkage between the 5’
phosphate of the “G” and the
2’ OH of the “A