Describe the process of transcription (initiation, elongation, termination, posttranscriptional modifications)

Question 1

What occurs during termination of transcription?

Answer 1

1. Transcription continues until RNA polymerase reaches a terminator sequence on the DNA.
2. This sequence signals the RNA polymerase to stop transcribing.
3. The RNA polymerase detaches, and the RNA molecule, now called pre-mRNA, is released.

Question 2

What occurs during initiation of transcription?

Answer 2

1. Transcription begins at a region upstream of the gene.
2. RNA polymerase binds to the promoter, a specific DNA sequence that marks the start of the gene.
3. The DNA unwinds, exposing the template strand, which will guide RNA synthesis.
4. The coding strand remains untranscribed but has the same sequence as the RNA being made (except thymine is replaced with uracil).

Question 3

What occurs during elongation of transcription?

Answer 3

1. RNA polymerase moves along the template strand, reading it in the 3’ to 5’ direction.
2. It synthesizes a complementary RNA strand in the 5’ to 3’ direction.
3. As it proceeds, adenine (A) in the DNA pairs with uracil (U) in the RNA, ensuring accurate transcription.

Question 4

What occurs during Post-transcriptional modifications of transcription?

Answer 4

** (Eukaryotes Only)**
1. A 5’ cap made of seven guanine molecules is added to the 5’ end of the pre-mRNA.
- a sequence of seven Gs that is added to the start of a pre-mRNA molecule; ribosomes recognize this site and use it as the site of initial attachment.
2. A poly-A tail (a string of adenine nucleotides) is added to the 3’ end.
- poly(A) tail a chain of adenine
nucleotides that are added to the 3’ end of the pre-mRNA molecule to protect it from enzymes in the cytosol.
3. Introns, or non-coding regions, are removed from the pre-mRNA.
4. Exons, or coding regions, are joined together.
5. This splicing process is performed by spliceosomes, molecular complexes that recognize and excise introns.
6. The resulting mRNA transcript is now mature and ready to be translated into a protein