Grade 12 University

Transcription is where a DNA strand is turned into a mRNA strand

 

mRNA is messenger rRNA and it tells what protein to code for (in translation)

 

1.Initiation 

RNA Polymerase binds onto the DNA at this special DNA sequence (TATA) called the promoter

• It is made up of A's and T's because recall that they only have 2 H bonds while C+G have 3...... 

  • ​Less bonds = less energy to break them

 

 

2. Elongation 

RNA Polymerase builds mRNA in the 5'-3' direction

• ​No primer used

• 1 strand is used and that is the template stand

  • ​unused = coding strand

 

DNA

 

5' CATATAC 3'  ---> Coding (not used)

 

3' G TATATG 5' ---> Template (used)

 

Initiation Sequence

 

.......................................................................................................................................................

 

mRNA

 

5' AUAUAC 3'                     *NOTE: template and mRNA = ANTIPARALLEL*

 

 

3. Termination 

RNA Polymerase stops at the terminator sequence then leaves

 

 

 

Post Transcirption modifications

 

These modifications are done to protect the mRNA

 

5' cap added

= 7 G's and protect mRNA from digestion in the cytoplasm = SACRIFICIAL

 

Poly Tail added

Poly A Polymerase adds 50-250 A to protect mRNA from degration = SACRIFICIAL

 

Introns Cut out

Coding regions = extrons ---- Non-coding = Introns

 

SnRNP's bind onto introns and signal to remove them --> if not cut out the protein will not fold properly and therefore won't function right

 

The finished product:

 

5'  GGGGGGGAUAUACA(x50-250)  3'