Transcription

Question 1

What does transcription do?

Answer 1

Transcription transfers genetic information held in the DNA base sequence to the mRNA, where it will be translated into a sequence of amino acids in a polypeptide chain.

RNA polymerase uses one strand of DNA as a template (antisense strand) to build a matching mRNA strand. The mRNA strand is complimentary to the DNA strand, meaning they are identical, with a uracil base replacing a thymine base on the mRNA strand, also known as the sense strand.

Question 2

Initiation

Answer 2

Transcription is initiated when an RNA polymerase uses subunit binds to a DNA sequence called the promoter. The promoter helps position the enzyme on the antisense strand. The strength of the affinity between the promoter and RNA polymerase affects how often the gene is transcribed and the amount of protein that is produced. The rest of the RNA polymerase subunits then assemble, forming the active holoenzyme.

Question 3

Elongation

Answer 3

RNA polymerase holoenzyme unwinds and unzips the DNA, creating a complimentary mRNA strand using free ribonucleotides which are floating freely in the nucleus. These ribonucleotides pair with their complimentary DNA bases through hydrogen bonding. The holoenzyme then catalyses the formation of phosphodiester bonds between the ribonucleotides, creating an RNA strand with a sugar-phosphate backbone.

Question 4

Termination

Answer 4

Transcription ends when RNA polymerase reaches a specific termination sequence at the 5’ end of the gene. The mRNA detached from both the RNA polymerase and the DNA template, and the polymerase releases from the DNA, allowing the double helix to reform.

Question 5

Stages of transcription in order of occurrence?

Answer 5

Initiation, Elongation, Termination.