Protein Synthesis

1. Protein Synthesis Honors Biology (grab a textbook)

2. Protein Synthesis • Sometimes proteins need to be made but DNA is trapped inside nucleus • How does the “code” for making proteins get out?

3. DNA ---> RNA---> Protein • 1. Transcription - DNA is a template or pattern for making RNA • 2. RNA moves outside nucleus through pores • 3. Translation– RNA directs assembly of amino acids to form proteins

4. Transcription Step 1 • RNA polymerase binds to a “promoter” on the DNA; says where to “start” • DNA starts unwinding

5. Transcription Step 2 • RNA polymerase adds free RNA nucleotides (bases that are complementary to those on DNA strand) • A mRNA strand forms • Only involves a specific gene on DNA strand, not entire strand

6. Transcription Step 3 • RNA polymerase reaches a “termination” signal; says “stop” • RNA is released and DNA rewinds

7. Questions (don’t copy) • Where does transcription take place in the cell? • What is the product of transcription? • How much of the DNA strand is copied?

8. Types of RNA • Messenger RNA (mRNA) - carries “code” from DNA out of nucleus to a ribosome • Ribosomal RNA (rRNA) - makes up ribosome; the place where proteins are made • Transfer RNA (tRNA) - carries amino acids to the ribosome so protein can be made

9. The genetic code • The sequence of bases on mRNA determines how amino acids are put together • Genetic code - 3 bases together determine a specific amino acid • 3 bases on a mRNAcalled a “codon”

10. How it works • Page 207 • AUG on mRNA means “start” • If next bases are CAC, this codes for Histidine • If next bases are AGC, this codes for Serine • Are 3 “stop” codons

11. Translation (making proteins) • mRNA comes from nucleus and goes to a ribosome • If DNA code is: ATACGG • Then mRNA code is: UAUGCC (remember U is found in RNA, not T) Chargaff’s Rule: A pairs with T (or U) C pairs with G

12. Translation – Step 1 • mRNA moves along a ribosome • A tRNA arrives - on one end is the amino acid, on other end is anti-codon • codonof mRNA matches up to anticodon of tRNA (complementary)

13. Translation – Step 2 • Codon & anti-codon meet; tRNA releases amino acid • Next tRNAarrives; codon & anti-codon meet; another a.a. is released and forms peptide bond with adjacent a.a.

14. Translation – Step 3 • Enough amino acids bind together to form a polypeptide chain until a “stop” codon is reached • Chain falls off and a protein is made

15. Example • Original DNA = A-A-T-T-C-C-A-T-G • mRNA = U-U-A-A-G-G-U-A-C • tRNA= A-A-U-U-C-C-A-U-G • Amino acids the mRNA codon codes for: • UUA = leucine • AGG = lysine • UAC = tyrosine

16. Now you try… • Original DNA = G-C-T-T-A-G-C-T-A • mRNA = • tRNA = • Amino acids the mRNA codon codes for:?

17. Answers • Original DNA = G-C-T-T-A-G-C-T-A • mRNA = C-G-A-A-U-C-G-A-U • tRNA = G-C-U-U-A-G-C-U-A • Amino acids the mRNA codon codes for: • C-G-A = arginine • A-U-C = isoleucine • G-A-U = aspartic acid

18. Another one… • Original DNA = • mRNA = C-U-U-A-A-G-C-A-C • tRNA = • Amino acids the mRNA codon codes for:?

19. Answers • Original DNA = G-A-A-T-T-C-G-T-G • mRNA = C-U-U-A-A-G-C-A-C • tRNA = G-A-A-U-U-C-G-U-G • Amino acids the mRNA codon codes for: • C-U-U = leucine • A-A-G = lysine • C-A-C = histidine

20. One more… • Original DNA = • mRNA = • tRNA = C-C-G-U-U-A-U-G-A • Amino acids the mRNA codon codes for:?

21. Answers • Original DNA = C-C-G-T-T-A-T-G-A • mRNA = G-G-C-A-A-U-A-C-U • tRNA = C-C-G-U-U-A-U-G-A • Amino acids the mRNA codon codes for: • G-G-C = glycine • A-A-U = asparagine • A-C-U = threonine