1. From Gene to Protein A.P. Biology

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

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. Prokaryotic cell. In a cell lacking a nucleus, mRNA produced by transcription is immediately translated without additional processing. (a) TRANSLATION TRANSCRIPTION DNA mRNA Ribosome Polypeptide In prokaryotes – Transcription and translation occur together

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

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

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. Synthesis of an RNA Transcript The stages of transcription are –Initiation –Elongation –Termination Figure 17.7 Promoter Transcription unit RNA polymerase Start point 5353 3535 3535 5353 5353 3535 5353 3535 5 5 Rewound RNA transcript 3 3 Completed RNA transcript Unwound DNA RNA transcript Template strand of DNA DNA 1 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. 2 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. 3 Termination. Eventually, the RNA transcript is released, and the polymerase detaches from the DNA.

12. Elongation RNA polymerase Non-template strand of DNA RNA nucleotides 3 end C A E G C A A U T A G G T T A A C G U A T C A T CCA A T T G G 3 5 5 Newly made RNA Direction of transcription (“downstream”) Template strand of DNA

13. 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 Figure 17.8 TRANSCRIPTION RNA PROCESSING TRANSLATION DNA Pre-mRNA mRNA Ribosome Polypeptide TATAA A A ATATTTT TATA box Start point Template DNA strand 5 3 3 5 Transcription factors 5 3 3 5 Promoter 5 3 3 5 5 RNA polymerase II Transcription factors RNA transcript Transcription initiation complex Eukaryotic promoters 1 Several transcription factors 2 Additional transcription factors 3

14. 1.RNA polymerase separates the DNA strands at a promoter region on the DNA (TATA box) 2.RNA polymerase adds nucleotides in sequence to mRNA 3.RNA polymerase falls off the DNA at a terminator sequence on the DNA Transcription – Making a Copy of the DNA

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

16. Transcription of mRNA Complementary to DNA Step #2

17. 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 A modified guanine nucleotide added to the 5 end 50 to 250 adenine nucleotides added to the 3 end Protein-coding segment Polyadenylation signal Poly-A tail 3 UTR Stop codonStart codon 5 Cap 5 UTR AAUAAA AAA…AAA TRANSCRIPTION RNA PROCESSING DNA Pre-mRNA mRNA TRANSLATION Ribosome Polypeptide G P PP 5 3

18. RNA splicing – Removes introns and joins exons TRANSCRIPTION RNA PROCESSING DNA Pre-mRNA mRNA TRANSLATION Ribosome Polypeptide 5 Cap Exon Intron 1 5 30 31 Exon Intron 104105146 Exon 3 Poly-A tail Introns cut out and exons spliced together Coding segment 5 Cap 1 146 3 UTR Pre-mRNA mRNA Introns - Intervening sequence = Junk DNA Exons – Expressed sequence Ribozymes – Are catalytic RNA molecules that function as enzymes and can splice RNA

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. TRANSCRIPTION TRANSLATION DNA mRNA Ribosome Polypeptide Amino acids tRNA with amino acid attached Ribosome tRNA Anticodon mRNA Trp Phe Gly A G C A AA C C G U G GUUU GG C Codons 5 3 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. A tRNA molecule – Consists of a single RNA strand that is only about 80 nucleotides long – Is roughly L-shaped Figure 17.14a 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.) (a) 3 C C A C G C U U A A G ACA C C U * G C * * G UGU * C U * GA G G U * * A * A A G U C A G A C C * C GA G A G G G * * G A C U C * A U U U A G G C G 5 Amino acid attachment site Hydrogen bonds Anticodon A

24. (b) Three-dimensional structure Symbol used in this book Amino acid attachment site Hydrogen bonds Anticodon A AG 5 3 35 (c)

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) A site (Aminoacyl-tRNA binding site) E site (Exit site) mRNA binding site

30. Central Dogma in Biology

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