1. Transcription

2. What I need to know:- 1.What transcription is 2.The stages of transcription 3.The use of enzymes in transcription 4.To identify what an intron and exon is 5.The process of RNA splicing

3. Protein synthesis DNA (containing all the genetic material/coding) messengerRNA Protein “The middle man”

4. Transcription Transcription is the synthesis of mRNA from a section of DNA. The newly synthesised mRNA strand will contain the code to make a specific protein. The stages are : -

5. Transcription STAGE 1 – DNA double helix unwinds STAGE 2 – weak hydrogen bonds breaking between bases, causing DNA strands to separate STAGE 3 – free RNA nucleotides (moving freely in the nucleus) find complimentary pair on the DNA strand STAGE 4 – weak hydrogen bonds are formed between the new bases pairing STAGE 5 – strong chemical bonds are formed between the new RNA nucleotides, opposite the DNA. This allows a new strand to be formed

6. STAGE 6 – weak hydrogen bonds are breaking between DNA & RNA, allowing mRNA to break from the DNA template STAGE 7 – new mRNA strand is ready to be transported out of the nucleus into the cytoplasm STAGE 8 – weak hydrogen bonds reunite the two original DNA strands into a double helix again.

8. RNA polymerase This enzyme is responsible for transcription as it moves along the gene, unwinding and opening the DNA strand. It also forms the mRNA strand (template) by joining nucleotides together Nucleotides can only join at the 3’ end of the mRNA strand

9. Primary transcript of mRNA

10. Modifying the primary transcript A transcribed mRNA strand can be up to 8000 nucleotides long. How many of these nucleotides do you think are needed to make the protein?

11. Around 1200!! There are long sections of DNA that do not code for a polypeptide. These are called INTRONS. Introns are found between the sections of DNA that do code for the proteins. These coding regions are called EXONS Since the introns are not needed, they are cut out

12. RNA Splicing Mature transcript with continuous coding sequence of nucleotides

13. Animations http://highered.mcgraw- hill.com/sites/0072943696/student_view0/ch apter3/animation__mrna_synthesis__transcri ption___quiz_1_.html http://highered.mcgraw- hill.com/sites/0072943696/student_view0/ch apter3/animation__mrna_synthesis__transcri ption___quiz_1_.html http://www.educationscotland.gov.uk/highers ciences/humanbiology/animations/transcripti on.asp# http://www.educationscotland.gov.uk/highers ciences/humanbiology/animations/transcripti on.asp#

14. Now attempt the following questions 1)Draw a diagram of the mRNA strand that would be transcribed from section X of the DNA molecule below 2)What enzyme is responsible for transcription? 3)What is an intron and an exon? 4)Which of these is removed from the primary transcript of mRNA? By what process? Section x A T C G G G C C A A T T A G C C C G G T T A