1. Protein Synthesis: Transcription
Miss Richardson
SBI4U

2. Transcription Purpose: to produce a copy of a segment of genomic DNA
Location: Nucleus
Stages:
Initiation
Elongation
Termination
Transcription

3. Only one DNA strand is transcribed – the antisense/template strand
The other strand – the sense/coding strand has the same sequence as the mRNA (with T instead of U)
Initiation

4. Transcription factors guide the binding of the enzyme RNA polymerase to the promoter region and the helix separates
A sequence of approximately 40 bases, upstream from the gene
Contains high concentration of adenine and thymine bases
Initiation

5. RNA polymerase is like DNA polymerase but doesn’t need primers
It moves along unwinding & unzipping the template DNA strand, and assembles mRNA in the 5’ to 3’ direction
Ribonucleotides form H-bonds with complementary bases
Phosphodiester bonds form between the ribonucleotides
The resulting mRNA is the same as the coding DNA strand (with U replacing T)
100’s of mRNA molecules can be made from one gene at a time
Elongation

6. Elongation

7. RNA polymerase recognizes the termination sequence and new mRNA strand is released

8. Eukaryotic mRNA is modified with the aide of enzymes prior to translation
5’ end: 7 methylated guanosine cap the transcript to prevent digestion
3’ end: poly-A tail (200 adenines) added to stabilize molecule
Splicing: introns (non-coding regions) are removed by enzymes (spliceosomes)
exons (coding regions) are joined to form mature mRNA
mRNA Modifications