Chapter 13; RNA Splicing

Question 1

What is a coding sequence called?

Answer 1

Exons, and they are expressed

Question 2

What is a non-coding sequence calld?

Answer 2

Introns or INTeRupt coding sequences

Question 3

What is the centra dogma?

Answer 3

Information flows from DNA to RNA to Proteins

Question 4

Which organism is direct reading of amino acid sequence from DNA sequence only possible?

Answer 4

Only possible in bacteria and bacteriophages

Question 5

In this organism, the DNA sequence coding for amino acid sequence is often interrupted by noncoding sequences?

Answer 5

In eukaryotes…

Question 6

What type of sequence does not result in a protein being made?

Answer 6

Non-coding sequence

Question 7

What is the region called at the very end of a gene or pre-mRNA in Eukaryotes?

Answer 7

Noncoding region - and it’s at the 3’ end

Question 8

What is the region before the very first exon on Genomic DNA, pre-mRNA and Spiced mRNA?

Answer 8

The Promoter region that becomes the 5’ leader region. The key point is that all of the “introns” that started out in the genomic DNA, that went to pre-mRNA, is actually gone in spliced mRNA. The only regions that are conserved throughout are the very beginning region “promoter region/5’leader” and the “non-coding region” at the 3’ end. All of the introns in-between are gone in mRNA.

Question 9

What parts of Genomic DNA would you see, if you started out with mRNA, reverse transcribed it from a certain promoter, and cloned the sequence?

Answer 9

You would not see any introns, just the promoter region to the end of the exons (I am not sure if the noncoding region at the 5’ end stays or not)

Question 10

AVERAGE Number of introns per gene in eukaryotes, who has the greatest number?

Answer 10

H. Sapiens at 7.7 > M. Musculus at 7.5 > A. Thaliana > …

Question 11

How many introns per gene in yeast?

Answer 11

1 intron per gene

Question 12

What is the approximate nucleotide number in an Exon?

Answer 12

~150

Question 13

What is the approximate number of nucleotides in an intron?

Answer 13

800,000

Question 14

A mammalian DHFR gene’s pre-mRNA has 31kb. What would the approximate number of kb be in mRNA?

Answer 14

2kb..about 6% are actual coding sequences (exons)

Question 15

Where is the 5’ and 3’ splice side on a gene?

Answer 15

The 5’ splice site is the 5’ end of the INTRON, and the 3’ splice sits is the 3’ end of the INTRON. Notes that it is named with respect to the intron only, even though that is the portion that ends up degraded in the end (mRNA).

Question 16

What does “N” mean in the intron gene sequence?

Answer 16

“N” means any nucleotide

Question 17

What does “Y” mean in the intron gene sequence?

Answer 17

“Y” is for a PYrimidine C/U

Question 18

What does “R” mean in the gene sequence?

Answer 18

“R” is for a PuRine A/G

Question 19

What is Y11 mean in the intron sequence?

Answer 19

It is the Pyrimidine TRACT, there are a lot of pyrimidines there.

Question 20

Rewrite the branch point sequence YNYURAY?

Answer 20

(C/U)-(A/T/C/U)-(C/U)-(U)-(A/G)-(A)-(C/U)

Question 21

What is the chemical mechanism of spicing?

Answer 21

2’OH of the A on the branch point attacking alpha Phosphorus

Question 22

Why isn’t a 3’OH attacking from the A branch point?

Answer 22

Because it is RNA and RNA has a 2’ OH

Question 23

Last slide made: This is called a “transesterification.” Why?

Answer 23

??