Post Transcriptional Modification In Eukaryotes

Question 1

Pre-rRNA(45S) Synthesized by

Answer 1

RNA polymerase I.

Question 2

Pre-rRNAProcessing

Answer 2

Cleaved by ribonucleases (RNases)

Base and sugar modifications is carried out by small nucleolar RNAs (snoRNA)

Question 3

In tRNA a 16-nucleotide sequence at the 5’ end is cleaved by

Answer 3

RNase P

Question 4

A 14-nucleotide intron in the anticodon loop is removed by

Answer 4

Nucleases

Question 5

Uracil residues at the 3’ end are replaced by by the

Answer 5

CCA sequence

Found in all mature tRNAs

Question 6

Many bases are converted to

Answer 6

Characteristic modified bases

Question 7

RNA polymerase II synthesizes a primary RNA transcript called

Answer 7

heterogeneous nuclear RNA (hnRNA).

Question 8

co- and post- transcriptional modifications in the nucleus.

Answer 8

1. 5’ Capping
2. 3’ poly-A tail addition
3. Removal of introns (Splicing)

Question 9

7-methylguanosine added “backward” in a 5’→ 5’ triphosphate linkage.

Answer 9

5’ capping

The cap

Question 10

Addition of GMP by

Answer 10

Guanylyltransferase

Question 11

Cap methylation is catalyzed by

Answer 11

Guanine-7-methyltransferase.

Question 12

Cap function

Answer 12

– Stabilizes the mRNA.

– Initiation of translation.

Question 13

The hn-mRNA is cleaved after the

Answer 13

polyadenylation signal sequence” (AAUAAA) within the 3’UTR.

Question 14

Addition of poly-A tail is catalyzed by

Answer 14

polyadenylate polymerase (poly A Pol).

ATP is used as substrate.

Question 15

The poly A tail sequence is not

Answer 15

transcribed from the DNA

Question 16

Poly-A tail function

Answer 16

– Facilitate mRNA transport out of the nucleus

– Stabilizes the mRNA

– Aid in translation

Question 17

Removal of introns (non-coding sequences) and joining of exons (coding sequences) to form the mature mRNA

Answer 17

Splicing

Question 18

Intron structure At the 5’ splice site

Answer 18

5’ GU 3’

Question 19

Intron structure At the 3’ splice site

Answer 19

5’ AG 3’

Question 20

snRNPs

Answer 20

small nuclear ribonucleoproteins

Question 21

snRNPs

Answer 21

Consist of small nuclear RNAs (snRNA) associated with nuclear proteins.

Question 22

The Spliceosome

Answer 22

The molecular complex that accomplishes the splicing mechanism

Question 23

15% of all genetic disease are a result of mutations that affect

Answer 23

RNA splicing

Question 24

b0 thalassemia

Answer 24

Homozygous mutations in the 5’ or 3’ intronic splice junction
sequences of the hemoglobin gene —> totally abolish normal splicing.

Question 25

b+ thalassemia

Answer 25

Apointmutationthatchangesthesequenceinthepolyadenylation signal site of the hemoglobin gene from AAUAAA —> AACAAA.