PROTEIN SYNTHESIS

1. PROTEIN SYNTHESIS Transcription & Translation – ‘Patterns of Life’ pg 121-133

2. Introduction • DNA contains the code to make protein • DNA is in the nucleus • Protein is made in the ribosome • The information must get from the nucleus to the ribosome - mRNA

4. Nuclear envelope • Continuous with pores • rough endoplasmic reticulum and ribosomes.

6. Key Pieces of Equipment • DNA • RNA – 3 types • Messenger (mRNA) • Transfer (tRNA) • Ribosomal (rRNA) • RNA polymerase (protein)

7. RNA vs DNA • Single stranded • Thyamine (T) is replaced by Uracil(U) • A lot smaller • No oxygen molecule

8. RNA • Linear polymer • Bases: Purines (adenine & guanine) Pyrimidines (cytosine & uracil) • Most are single stranded, therefore does not form a double helix. Although can fold and twist into itself.

9. Messenger RNA • Codon a sequence of three nucleotides that code for a single amino acid • mRNA carries the code from the nucleus to the ribosome

10. Transfer RNA • Transfer RNA (tRNA): decodes the information • tRNA has an anti-codon which matches a specific codon of mRNA • Each tRNA attaches to a specific amino acid that compliments its anti-codon • There are 20 different tRNA types (one for each type of amino acid)

12. Ribosomal RNA • Ribosomal RNA (rRNA): makes up approximately 50% of a ribosome. • The assembly place of protein synthesis.

13. Ribosome • 2 subunits – heavy and light

14. The Genetic Code • 20 different amino acids used to produce proteins. • The code for a specific amino acid is controlled by the 4 different nucleotides (T,C,A,G) in the DNA. • This code goes in sequences of three (Triplets) • A triplet codes for a single amino acid • WHY?

15. These triplets produce codons in mRNA • A codon codes for a specific amino acid • Some combinations act as STOP (UAA, UGA, UAG) and START (AUG) signals. • One codon is the start codon - AUG

16. Genetic Code cont.

17. Protein Synthesis-the process • Two parts to protein synthesis: • Translation of mRNA from DNA • Occors in the nucleus • Transcription of mRNA into a polypeptide chain • Occurs at the ribosome

19. Transcription • One section of DNA unwinds. One side acts as a template for the mRNA to be synthesised.

20. The RNA polymerase reads the DNA from 3’ end of the DNA. • RNA polymerase then binds complementary bases to form the mRNA.

22. Codes on the DNA act as punctuation, indicating beginning and end of protein and transcription. • Once termination sequence reached, transcription ceases. The mRNA is then completed and it travels out of the nucleus to the ribosome

24. Translation • mRNA becomes bound to a ribosome. • The mRNA’s strand is placed in the ‘P’ site (the first position on a ribosome)

25. Next to the ‘P’ site is the ‘A’ site. • Both sites hold one tRNA molecule. • Once the start codon is placed into the ‘P’ site, translation occurs.

26. Next a tRNA fits into the ‘P’ site based upon the codon on the mRNA lined up on the ‘P’ site. • Another tRNA fits into the ‘A’ site also based on the codon on the mRNA at the ‘A’ site.

27. When both sites have a tRNA present, the amino acids on the tRNA bond together to form the first link of a protein chain.

28. Once the two amino acids have linked together: • The tRNA in the P site is released • The mRNA moves codon so the tRNA in the ‘A’ site is shifted into the ‘P’ site.

29. The ‘A’ site is now clear so a new tRNA molecule moves in corresponding to the mRNA • This amino acid links to the protein chain. • This process continues until a stop codon is read at the ‘A’ site.

30. Termination • Once a stop codon is read at the ‘A’ site, the ribosome has finished synthesising the protein. • A new tRNA molecule is not added to the protein chain. • The two ribosome units separate. • Protein chain released from ribosome.

32. Protein synthesis animation • http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter15/animations.html#