Protein Synthesis

1. Protein Synthesis Transcription and Translation Mader Biology Chapter 14

2. Protein synthesis = Central dogma= DNA To RNA TO protein Transcription: DNA transcribes code to mRNA in nucleus Translation: tRNA transports amino acids to mRNA on ribosome, builds polypeptide

3. 3 rna’s used to make proteins • mRNA – carries the “message” of DNA • Travels from nucleus to cytoplasm • Takes message to ribosome for protein synthesis • tRNA – transfer RNA – brings amino acids to ribosome for protein synthesis • rRNA – ribosomal RNA – what ribosome is made of

4. Amino acid attachment site A A G 3 5 Anticodon Symbol used in some books The tRNA molecule

5. Nuclear envelope DNA TRANSCRIPTION DNA TRANSCRIPTION mRNA Ribosome Pre-mRNA RNA PROCESSING TRANSLATION mRNA Polypeptide Ribosome (a) TRANSLATION Polypeptide (b) Transcription and translation • In eukaryotes, separated by nuclear envelope • In prokaryotes, occurs together

6. transcription DNA mRNA

7. Non-template strand of DNA Elongation RNA nucleotides RNA polymerase T A C C A T A T C 3 U 3 end T G A U G G A G A C C C T A 5 A A T A G G T T Template strand of DNA 5 Direction of transcription (“downstream”) Newly made RNA Transcription • Transfer of genetic information from DNA to RNA (mRNA) • Similar to replication: • The DNA strands must separate • Nitrogen bases are paired with their opposite • Unlike replication: • Carried out by RNA polymerase (not DNA polymerase) • Only 1 mRNA strand created, not 2 • Leading strand only • Thymine  Uracil

9. More Transcription • Promoter- region where RNA polymerase attaches and initiates transcription • Often a sequence of TATA – known as the TATA box • Terminator- DNA sequence that signals the end of transcription

10. transcription DNA mRNA

11. DNA TRANSCRIPTION mRNA Ribosome TRANSLATION Polypeptide Amino acids Polypeptide tRNA with amino acid attached Ribosome Trp Phe Gly tRNA C C C G G Anticodon A A A A G G G U G U U U C Codons 5 3 mRNA Translation • mRNA  protein • Takes place on ribosome in cytoplasm • Video here

12. Translation: Genetic Information is “read” • DNA = letters A, C, T, G (you know this!) • These bases are encoded as a sequence base triplets, or codons, each of which is translated into a specific amino acid • FOR EXAMPLE: • Theredfoxatetherat = the red fox ate the rat • AUGCCTUGUCGA = AUG CCT UGU CGA (easier, huh?)

13. Translation: Genetic information is “read” • Codons = genetic code • Translates to amino acids (proteins) • Codon chart is universal for all living organisms (see pink sheet) • So, let’s take the DNA sequence: • TACGGT • mRNA sequence? • Amino acid sequence? • *see chart

14. How does translation happen?3 stage process

15. Large ribosomal subunit P site 5 3 U C A Met Met 3 A 5 G U Initiator tRNA GDP GTP E A mRNA 5 5 3 3 Start codon mRNA binding site Small ribosomal subunit Translation initiation complex 1) Initiation • 1) Initiation • Brings together mRNA, tRNA and ribosome • Begins at the start codon, AUG

16. Amino end of polypeptide 1 Codon recognition DNA TRANSCRIPTION mRNA Ribosome TRANSLATION Polypeptide E mRNA 3 Ribosome ready for next aminoacyl tRNA P A site site 5 GTP 2 GDP 2 E E P A P A 2 GDP Peptide bond formation Translocation. 3 GTP E P A 2) Elongation • Codon of mRNA and anticodon of tRNA complementary bond to one another • Peptide bond formation • Translocation-ribosome moves to next codon

17. Release factor Free polypeptide 5 3 3 3 5 5 Stop codon (UAG, UAA, or UGA) The release factor hydrolyzes the bond between the tRNA in the P site and the last amino acid of the polypeptide chain. The polypeptide is thus freed from the ribosome. When a ribosome reaches a stop codon on mRNA, the A site of the ribosome accepts a protein called a release factor instead of tRNA. The two ribosomal subunits and the other components of the assembly dissociate. 2 1 3 3) Termination • mRNA stop codons - UAA, UAG, UGA

19. Protein synthesis and mutation • Mutation = Permanent, (sometimes) heritable DNA change • Mutagens: • Chemical mutagens (alcohol, tobacco, drugs) • Increases rate to 1 in 1000-100,000) • Radiation • X rays, gamma rays break DNA, bases • UV light causes knots in DNA strand • Spontaneous mutations • Occurs in DNA replication (1 in 109 bp) • Polymerase makes mistakes

20. Protein Synthesis and Mutation • Point mutation (base substitutions) • Can have many effects: • Missense mutation • Nonsense mutation • Run-on • Silent mutation • Frameshift mutations (Insertions or deletions) • Dramatic change in amino acids • Run-ons, premature stops (nonsense mut.)

21. Point Mutation - Substitutions • A substitution of one base for another This can have many different effects: • Missence • Nonsense • Run-on • Silent

22. Missense mutation • Changes an amino acid in the sequence

23. Nonsense mutation • Prematurely stops the amino acid sequence

24. Run-on mutation • Continues the sequence that was supposed to end G C Glu

25. Silent mutation • No effect on the amino acids G C

26. Frameshift Mutations – Insertions or deletions THEBIGCATATETHERAT = THE BIG CAT ATE THE RAT THEBIGCBATATETHERAT = THE BIG CBA TAT ETH ERA T

27. Summary: Mutations POINT mutations-one base pair is changed • Substitutions FRAMESHIFT: • Insertions (additions) • Deletions