Lecture 10 - RNA Processing_final

Question 1

What are constitutive exons?

Answer 1

Present in every transcript

Constitutive exons are essential components of mature mRNA.

Question 2

What are cassette exons?

Answer 2

Choose only one of the group

Cassette exons contribute to alternative splicing variations.

Question 3

What is the lariat structure in splicing?

Answer 3

Branched structure of an excised intron

The lariat is formed during the splicing process.

Question 4

What type of bond is formed during the splicing reaction?

Answer 4

2’-5’ phosphodiester bond

This bond links the branch site to the intron.

Question 5

What is the role of splice sites?

Answer 5

Serve as recognition signals to the splicing machinery

These sequences are conserved in all eukaryotes.

Question 6

True or false: Mutations in splice site sequences generally enhance splicing.

Answer 6

FALSE

Mutations typically abolish splicing efficiency.

Question 7

What is the function of the spliceosome?

Answer 7

Removes introns from pre-mRNA

The spliceosome is composed of snRNPs and proteins.

Question 8

What do snRNPs contain?

Answer 8

• One snRNA
• 7-15 proteins

snRNPs are essential for the formation of a catalytically active spliceosome.

Question 9

What is the catalytic site of the spliceosome primarily formed by?

Answer 9

RNAs, not by proteins

This distinguishes spliceosomes from ribosomes.

Question 10

What are the two recognition factors in splicing?

Answer 10

• U1: finds the 5’ splice site
• U2: finds the branch site

These factors are crucial for spliceosome assembly.

Question 11

What happens in the first reaction of pre-mRNA splicing?

Answer 11

• Bond between last nucleotide of exon 1 and first nucleotide of intron is broken
• New 2’-5’ bond is formed

This reaction initiates the splicing process.

Question 12

What occurs in the second reaction of pre-mRNA splicing?

Answer 12

• Bond between last nucleotide of intron and first nucleotide of exon 2 is broken
• New 3’-5’ bond is formed

This completes the splicing process, releasing the intron.

Question 13

What is the significance of alternative splicing?

Answer 13

Allows the proteome to be bigger than the genome

This process generates protein isoforms that can modulate function.

Question 14

What are Group I introns known for?

Answer 14

Self-splicing RNAs

They fold into a catalytically active structure.

Question 15

What distinguishes Group II introns from Group I introns?

Answer 15

Closely resemble pre-mRNA introns

They use a similar two-step mechanism for splicing.

Question 16

What is the role of maturases in splicing?

Answer 16

Enhance the rate of splicing

Maturases are proteins that assist in the splicing process.

Question 17

What is the function of the 5’ cap in mRNA?

Answer 17

Protects the 5’ end from nucleases

The cap is crucial for mRNA stability and translation.

Question 18

What does the poly(A) tail do?

Answer 18

Protects the 3’ end from nucleases

It regulates the half-life of mRNA in the cytoplasm.

Question 19

What is the significance of RNA processing in eukaryotes?

Answer 19

Eukaryotic mRNAs undergo many processing steps

This includes capping, polyadenylation, and splicing.

Question 20

What are the two components required for efficient translation of an mRNA?

Answer 20

• Cap
• Poly(A) tail

Both components communicate with each other during the translation process.

Question 21

The largest subunit of RNA polymerase II has a long ________ tail.

Answer 21

carboxy-terminal

This tail must be unphosphorylated for Pol II to initiate transcription.

Question 22

What enzyme phosphorylates the amino acids on the carboxy-terminal tail of RNA polymerase II?

Answer 22

TFIIH

Phosphorylation by TFIIH allows Pol II to release from the initiation complex.

Question 23

What are the two ends of eukaryotic mRNAs formed during processing?

Answer 23

• 5’ cap
• 3’ poly(A) tail

These modifications are crucial for mRNA stability and translation.

Question 24

What process involves the removal of introns from RNAs?

Answer 24

Splicing

This process links exons together to form mature mRNA.

Question 25

Name the **three different splicing mechanisms** identified.

Answer 25

* Group I intron splicing * Group II intron splicing * Spliceosome ## Footnote All mechanisms involve the removal of intron RNA.

Question 26

What structure protects the **5’ end** of an mRNA?

Answer 26

Cap structure ## Footnote A single non-templated G residue is added to the 5’ end of the pre-mRNA.

Question 27

What enzyme adds GMP in an unusual **5’-5’ triphosphate linkage**?

Answer 27

Guanylyl transferase ## Footnote This enzyme is involved in the capping process of mRNA.

Question 28

What do **methyl transferases** do to the G added to the 5’ end of pre-mRNA?

Answer 28

Add one or more methyl groups ## Footnote This modification is part of the capping process.

Question 29

What are the **polyadenylation factors** that ride along on the phosphorylated carboxy-terminal tail of RNA polymerase II?

Answer 29

* CPSF * CStF ## Footnote CPSF stands for cleavage and polyadenylation specificity factor, while CStF stands for cleavage stimulation factor.

Question 30

What directs **cleavage and polyadenylation** near the 3’ end of the pre-mRNA?

Answer 30

Polyadenylation signal ## Footnote This signal is encoded in the DNA.

Question 31

What is the first step in **mRNA processing**?

Answer 31

5’ capping ## Footnote Caps are added to pol II transcripts shortly after initiation.

Question 32

When does the capping process begin during mRNA processing?

Answer 32

When the nascent pre-mRNA is about 25 nucleotides long ## Footnote Capping enzymes ride along on the phosphorylated tail of the pol II large subunit.

Question 33

What type of linkage is used when the G is put on the 5’ end of mRNA?

Answer 33

5’-5’ linkage ## Footnote This is referred to as a 'backwards' linkage.