transcription

Question 1

transcription

Answer 1

transfer of genetic information from DNA into an RNA molecule (initiation, elongation, termination)

Question 2

features of transcription

Answer 2

o Occurs in the nucleus
o A complementary code is made by building a molecule of mRNA
o DNA triplet codes are transcribed into codons in mRNA
o Catalysed by RNA polymerase

Question 3

Initiation

Answer 3

o Double helix unwinds and the hydrogen bonds are broken at the site of the gene being transcribed
o RNA polymerase recognizes and binds to a “start” signal
o The “start” signal is a nucleotides sequence called a promoter located at the beginning of a gene
o A promoter is a sequence of DNA to which proteins bind to initiate transcription of single RNA transcript from the DNA

Question 4

Elongation

Answer 4

o Template strand (3’ -> 5’) is used as the templated for transcription
o RNA polymerase matches free nucleotides by complementary base pairing (A with U; C with G), working in the 5’ -> 3’ direction (make the coding strand)
o Hydrogen bonds then form between complementary bases
o Each free nucleotide is then joined by a condensation reaction between the sugar and the phosphate groups of adjacent nucleotides of the RNA strand

Question 5

Termination

Answer 5

o When RNA polymerase reaches a special sequence, called as terminator, on the template strand, transcription is terminated
o mRNA is released and leaves nucleus through pores in nuclear enveloped and passes to ribosomes in the cytoplasm
o A terminator is a sequence of DNA that marks the end of a gene during transcription