1. TOPIC 2.7 TRANSCRIPTION & TRANSLATION

2. Nucleus: the control center  contains nuclear envelope, nucleoli, chromatin, and distinct compartments rich in specific protein sets  genetic library with blueprints for nearly all cellular proteins  dictates the kinds and amounts of proteins to be synthesized

3. Structure of DNA Figure 2.22b

4. DNA to mRNA to protein  DNA  genetic library with blueprints for proteins  transcribed into mRNA  mRNA  translated into polypeptides using rRNA and tRNA

5. Figure 3.34 Coding strand Template strand Promoter Termination signal Transcription unit In a process mediated by a transcription factor, RNA polymerase binds to promoter and unwinds 16–18 base pairs of the DNA template strand RNA polymerase Unwound DNA RNA nucleotides RNA polymerase bound to promoter mRNA synthesis begins RNA polymerase moves down DNA; mRNA elongates RNA nucleotides mRNA synthesis is terminated RNA polymerase mRNA DNA mRNA transcript (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

6. Figure 3.34 Coding strand Template strand Promoter Termination signal Transcription unit (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

7. Figure 3.34 Coding strand Template strand Promoter Termination signal Transcription unit In a process mediated by a transcription factor, RNA polymerase binds to promoter and unwinds 16–18 base pairs of the DNA template strand RNA polymerase Unwound DNA RNA polymerase bound to promoter (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

8. Figure 3.34 Coding strand Template strand Promoter Termination signal Transcription unit In a process mediated by a transcription factor, RNA polymerase binds to promoter and unwinds 16–18 base pairs of the DNA template strand RNA polymerase Unwound DNA RNA nucleotides RNA polymerase bound to promoter mRNA synthesis begins (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

9. Figure 3.34 Coding strand Template strand Promoter Termination signal Transcription unit In a process mediated by a transcription factor, RNA polymerase binds to promoter and unwinds 16–18 base pairs of the DNA template strand RNA polymerase Unwound DNA RNA nucleotides RNA polymerase bound to promoter mRNA synthesis begins mRNA (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

10. Figure 3.34 Coding strand Template strand Promoter Termination signal Transcription unit In a process mediated by a transcription factor, RNA polymerase binds to promoter and unwinds 16–18 base pairs of the DNA template strand RNA polymerase Unwound DNA RNA nucleotides RNA polymerase bound to promoter mRNA synthesis begins RNA polymerase moves down DNA; mRNA elongates RNA nucleotides mRNA (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

11. Figure 3.34 Coding strand Template strand Promoter Termination signal Transcription unit In a process mediated by a transcription factor, RNA polymerase binds to promoter and unwinds 16–18 base pairs of the DNA template strand RNA polymerase Unwound DNA RNA nucleotides RNA polymerase bound to promoter mRNA synthesis begins RNA polymerase moves down DNA; mRNA elongates RNA nucleotides mRNA synthesis is terminated RNA polymerase mRNA DNA mRNA transcript (a) RNA nucleotides RNA polymerase Unwinding of DNA Coding strand Rewinding of DNA mRNA RNA-DNA hybrid region Template strand (b)

12. Roles of the Three Types of RNA  Messenger RNA (mRNA) – carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm  Transfer RNAs (tRNAs) – bound to amino acids base pair with the codons of mRNA at the ribosome to begin the process of protein synthesis  Ribosomal RNA (rRNA) – a structural component of ribosomes

13. Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Amino acids tRNA Aminoacyl-tRNA synthetase tRNA “head” bearing anticodon Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus Once its amino acid is released, tRNA is ratcheted to the E site and then released to reenter the cytoplasmic pool, ready to be recharged with a new amino acid. Incoming aminoacyl- tRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain and the tRNA in the A site is translocated to the P site. Codon 16Codon 15Codon 17 Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. 1 2 3 4

14. Figure 3.36 Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Nucleus

15. Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus Codon 16Codon 15Codon 17 1

16. Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Amino acids tRNA Aminoacyl-tRNA synthetase Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus Codon 16Codon 15Codon 17 1 Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme.

17. Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Amino acids tRNA Aminoacyl-tRNA synthetase tRNA “head” bearing anticodon Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus Incoming aminoacyl- tRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. Codon 16Codon 15Codon 17 Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. 1 2

18. Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Amino acids tRNA Aminoacyl-tRNA synthetase tRNA “head” bearing anticodon Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus Incoming aminoacyl- tRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain and the tRNA in the A site is translocated to the P site. Codon 16Codon 15Codon 17 Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. 1 2 3

19. Figure 3.36 After mRNA processing, mRNA leaves nucleus and attaches to ribosome, and translation begins. Amino acids tRNA Aminoacyl-tRNA synthetase tRNA “head” bearing anticodon Large ribosomal subunit Small ribosomal subunit Released mRNA mRNA Template strand of DNA RNA polymerase Nuclear pore Nuclear membrane Portion of mRNA already translated Direction of ribosome advance Nucleus Once its amino acid is released, tRNA is ratcheted to the E site and then released to reenter the cytoplasmic pool, ready to be recharged with a new amino acid. Incoming aminoacyl- tRNA hydrogen bonds via its anticodon to complementary mRNA sequence (codon) at the A site on the ribosome. As the ribosome moves along the mRNA, a new amino acid is added to the growing protein chain and the tRNA in the A site is translocated to the P site. Codon 16Codon 15Codon 17 Energized by ATP, the correct amino acid is attached to each species of tRNA by aminoacyl-tRNA synthetase enzyme. 1 2 3 4

20. Genetic Code  RNA codons code for amino acids according to a genetic code Figure 3.35

21. Information Transfer from DNA to RNA  DNA triplets are transcribed into mRNA codons by RNA polymerase  Codons base pair with tRNA anticodons at the ribosomes  Amino acids are peptide bonded at the ribosomes to form polypeptide chains  Start and stop codons are used in initiating and ending translation

22. Information Transfer from DNA to RNA Figure 3.38