Genes and transcription (2)

Question 1

RNA processing

Answer 1

1. Addition of a5’ capto the beginning of the RNA
2. Addition of apoly-A tail(tail of A nucleotides) to the end of the RNA
3. Removal ofintron sequences, and joining together of the exon sequences

Question 2

what is special about hte 5’ cap

Answer 2

cap is a modified guanine (G) nucleotide, and it protects the transcript from being broken down

Question 3

While RNA Polymerase II is still transcribing downstream of the proper end of a gene.. what is happening then?

Answer 3

the pre-mRNA is cleaved by an endonuclease-containing protein complex

This releases the functional pre-mRNA from the rest of the transcript, which is still attached to the RNA Polymerase

Question 4

Splicing - removal ofintron sequences (II)

Answer 4

Includes exons and untranslated regions (introns)

Primary RNA transcript undergoes a form of processing called RNA splicing

Question 5

How does the cell know where to cut the RNA during RNA splicing

Answer 5

When a cell makes a messenger RNA (mRNA) from a gene, it includes both coding parts (exons) and non-coding parts (introns). RNA splicing is like editing out the non-coding parts to create a final mRNA that can be used to make proteins.

To remove the introns, the cell cuts the RNA at specific points called splice sites. These sites mark where the exons end and the introns begin.

Certain sequences of DNA are like signals that tell the cell where to cut the RNA.

the beginning of an intron on the DNA strand starts with “GT” and ends with “AG.” When this DNA is transcribed into RNA, it creates a sequence starting with “GU” (splice donor site) and ending with “AG” (splice acceptor site).

Question 6

how is RNA splicing achieved

Answer 6

using splicesosomes