From Gene to Protein

1. From Gene to Protein A.P. Biology

2. Typical Gene Structure Promoter(RNA polymerase binding site) Regulatory sites DNA strand Start transcription Stop transcription

3. RNA • Contains ribose instead of deoxyribose • Single stranded • Nucleotide uracil replaces thymine

4. 3 Types of RNA • Messenger RNA = mRNA -Carries DNA sequence to the ribosome • Ribosomal RNA = rRNA -Component of ribosome • Transfer RNA = tRNA -Carries amino acid (anticodon) to the codon on mRNA

5. Basic Principles of Transcription and Translation • Transcription • Is the synthesis of RNA under the direction of DNA • Produces messenger RNA (mRNA) • Translation • Is the actual synthesis of a polypeptide, which occurs under the direction of mRNA • Occurs on ribosomes

6. DNA TRANSCRIPTION mRNA Ribosome TRANSLATION Polypeptide Prokaryotic cell. In a cell lacking a nucleus, mRNAproduced by transcription is immediately translatedwithout additional processing. (a) • In prokaryotes • Transcription and translation occur together

7. Nuclear envelope DNA TRANSCRIPTION Pre-mRNA RNA PROCESSING mRNA Ribosome TRANSLATION (b) Eukaryotic cell. The nucleus provides a separatecompartment for transcription. The original RNAtranscript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA. Polypeptide Figure 17.3b • In eukaryotes • RNA transcripts are modified before becoming true mRNA

8. Gene 2 DNA molecule Gene 1 Gene 3 DNA strand (template) 5 3 A C C T A A A C C G A G TRANSCRIPTION A U C G C U G G G U U U 5 mRNA 3 Codon TRANSLATION Gly Phe Protein Trp Ser Figure 17.4 Amino acid • During transcription • The gene determines the sequence of bases along the length of an mRNA molecule

9. In laboratory experiments • Genes can be transcribed and translated after being transplanted from one species to another

10. Molecular Components of Transcription • RNA synthesis • Is catalyzed by RNA polymerase, which pries the DNA strands apart and hooks together the RNA nucleotides • Follows the same base-pairing rules as DNA, except that in RNA, uracil substitutes for thymine

11. 3 1 2 Promoter Transcription unit 5 3 3 5 Start point DNA RNA polymerase Initiation. After RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand. Template strand of DNA 5 3 3 5 Unwound DNA RNA transcript Elongation. The polymerase moves downstream, unwinding the DNA and elongating the RNA transcript 5 3 . In the wake of transcription, the DNA strands re-form a double helix. Rewound RNA 5 3 3 5 3 RNA transcript 5 Termination. Eventually, the RNA transcript is released, and the polymerase detaches from the DNA. 5 3 3 5 3 5 Completed RNA transcript Figure 17.7 Synthesis of an RNA Transcript • The stages of transcription are • Initiation • Elongation • Termination

12. 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 E A C C C A 5 A A T A G G T T Direction of transcription (“downstream”) 5 Template strand of DNA Newly made RNA

13. Eukaryotic promoters 1 TRANSCRIPTION DNA Pre-mRNA RNA PROCESSING mRNA Ribosome TRANSLATION Polypeptide Promoter 5 3 A T A T A A A A T A T T T T 3 5 TATA box Start point Template DNA strand Several transcription factors 2 Transcription factors 5 3 3 5 Additional transcription factors 3 RNA polymerase II Transcription factors 3 5 5 3 5 RNA transcript Figure 17.8 Transcription initiation complex RNA Polymerase Binding and Initiation of Transcription • Promoters signal the initiation of RNA synthesis • Transcription factors • Help eukaryotic RNA polymerase recognize promoter sequences • TATA box

14. Transcription – Making a Copy of the DNA • RNA polymerase separates the DNA strands at a promoter region on the DNA (TATA box) • RNA polymerase adds nucleotides in sequence to mRNA • RNA polymerase falls off the DNA at a terminator sequence on the DNA

15. Unwinding of the DNA Helix by RNA Polymerase Step #1

16. Transcription of mRNA Complementary to DNA Step #2

17. A modified guanine nucleotide added to the 5 end 50 to 250 adenine nucleotides added to the 3 end TRANSCRIPTION DNA Polyadenylation signal Protein-coding segment Pre-mRNA RNA PROCESSING 5 3 mRNA G P P AAA…AAA P AAUAAA Ribosome Start codon Stop codon TRANSLATION Poly-A tail 5 Cap 5 UTR 3 UTR Polypeptide Alteration of mRNA Ends • Each end of a pre-mRNA molecule is modified • The 5 end receives a modified nucleotide cap • The 3 end gets a poly-A tail

18. RNA splicing • Removes introns and joins exons Intron Exon 5 Exon Intron Exon 3 5 Cap Poly-A tail Pre-mRNA TRANSCRIPTION DNA 30 31 104 105 146 1 Pre-mRNA RNA PROCESSING Introns cut out and exons spliced together Coding segment mRNA Ribosome TRANSLATION 5 Cap Poly-A tail mRNA Polypeptide 1 146 3 UTR 3 UTR • Ribozymes • Are catalytic RNA molecules that function as enzymes and can splice RNA Introns - Intervening sequence = Junk DNA Exons – Expressed sequence

20. mRNA Processing in Eukaryotic Cells

21. Molecular Components of Translation • A cell translates an mRNA message into protein • With the help of transfer RNA (tRNA)

22. 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 • Molecules of tRNA are not all identical • Each carries a specific amino acid on one end • Each has an anticodon on the other end

23. 3 A Amino acid attachment site C C 5 A C G C G C G U G U A A U U A U C G * G U A C A C A * A U C C * G * U G U G G * G A C C G * C A G * U G * * G A G C Hydrogen bonds (a) G Two-dimensional structure. The four base-paired regions and three loops are characteristic of all tRNAs, as is the base sequence of the amino acid attachment site at the 3 end. The anticodon triplet is unique to each tRNA type. (The asterisks mark bases that have been chemically modified, a characteristic of tRNA.) C U A G * A * A C * U A G A Anticodon Figure 17.14a • A tRNA molecule • Consists of a single RNA strand that is only about 80 nucleotides long • Is roughly L-shaped

24. Amino acid attachment site 5 3 Hydrogen bonds A A G 3 5 Anticodon Anticodon (c) Symbol used in this book (b) Three-dimensional structure

25. A specific enzyme called an aminoacyl-tRNA synthetase • Joins each amino acid to the correct tRNA

26. The ribosome • Is part of the cellular machinery for translation, polypeptide synthesis • Facilitates the specific coupling of tRNA anticodons with mRNA codons during protein synthesis

27. The ribosome has three binding sites for tRNA • The P site • The A site • The E site P site (Peptidyl-tRNA binding site) E site (Exit site) mRNA binding site A site (Aminoacyl-tRNA binding site)

30. Central Dogma in Biology

31. Gene Mutations: Substitution, Insertion, & Deletion Deletion Substitution Insertion Point Mutation Frameshift Mutation

32. Base Pair Substitution • Missense mutation – altered codon codes for a different amino acid • Nonsense mutation – altered codon changed to a stop codon (no amino acid delivered)

33. Chromosomal Mutations Deletion Duplication Inversion Translocation