6.3 continued: pre-mRNA modifications

Question 1

What are pre-mRNA modifications?

Answer 1

modifications that must occur to eukaryotic pre-mRNA before it is ready for translation

Question 2

Pre-mRNA modifications: what occurs in 5’ cap (GTP)? (2)

Answer 2

• guanosine triphosphate (nucleoside triphosphate)

- the 5’ end of the pre-mRNA receives a modified guanine nucleotide “cap”

Question 3

Pre-mRNA modifications: what occurs in the Poly-A tail? (2)

Answer 3

• Poly-A means many adenine

- the 3’ end of the pre-mRNA receives 50 to 250 adenine nucleotides

Question 4

How do the 5’ cap and the poly-A tail function together? (3)

Answer 4

• help the mature mRNA leave the nucleus
• help protect the mRNA from degradation
• help ribosomes attached to the 5’ end of the mRNA when it reaches the cytoplasm

Question 5

Pre-mRNA modifications: What occurs in RNA splicing?

Answer 5

• sections of the pre-mRNA called Introns are removed and then exons are joined together

Question 6

What are Introns?

Answer 6

Intervening sequence do not code for amino acids

Question 7

What are exons?

Answer 7

Expressed sections, code for amino acids

Question 8

What are the three modifications that must occur to eukaryotic pre-mRNA before it is ready for translation?

Answer 8

• 5’ cap (GTP)
• Poly-A tail
• RNA splicing

Question 9

Why does RNA splicing occur? (2)

Answer 9

• Single gene can code for more than one kind of polypeptide

- Known as alternative splicing