1. From DNA to Proteins Chapter 13

2. Central Dogma DNA RNA Protein

3. Same two steps produce all proteins: 1) DNA is transcribed to form RNA –Occurs in the nucleus –RNA moves into cytoplasm 2) RNA is translated to form polypeptide chains, which fold to form proteins Steps from DNA to Proteins

4. Three Classes of RNAs Messenger RNA (mRNA) –Carries protein-building instruction Ribosomal RNA (rRNA) –Major component of ribosomes Transfer RNA (tRNA) –Delivers amino acids to ribosomes

5. DNA vs RNA 1) Sugar (ribose) differs –DNA sugar is deoxyribose (missing O) –RNA sugar is ribose 2) Possible bases differ –DNA uses bases A, C, G, T –RNA uses bases A, C, G, U 3) DNA stable as double-stranded structure RNA stable as single-stranded structure

6. A Nucleotide Subunit of RNA

7. Base Pairing during Transcription A new RNA strand can be put together on a DNA region according to base- pairing rules As in DNA, C-G, but A-T does not exist Uracil (U) pairs with adenine (A)

8. Transcription & DNA Replication Like DNA replication –Nucleotides added to growing RNA strand in the 5’ to 3’ direction Unlike DNA replication –Small in length compared to DNA –RNA polymerase makes RNA from DNA –Product is a single strand of RNA

9. Base Pairing Compared

10. Promoter - place where RNA polymerase binds A base sequence in the DNA that signals the start of a gene For transcription to occur, RNA polymerase must first bind to a promoter promoter region

11. Gene Transcription DNA template winding up DNA template unwinding newly forming RNA transcript DNA template at selected transcription site

12. Adding Nucleotides 3´ 5´ direction of transcription 5´ 3´ growing RNA transcript

13. Transcript Modification

14. Genetic Code Set of 64 base triplets Codons –Nucleotide bases read in blocks of three 61 specify amino acids 3 stop translation

15. Code Is Redundant Twenty (20) kinds of amino acids are specified by 61 codons Most amino acids can be specified by more than one codon i.e. six codons specify leucine –UUA, UUG, CUU, CUC, CUA, CUG

16. Near-Universal Genetic Code AUG AAA CGA UGA

17. tRNA Structure - brings 20 different amino acids to ribosome There are at least 20 different populations of tRNAs inside the cytoplasm of the cell.

18. Ribosomes - structures where proteins are made

19. Three Stages of Translation Initiation Elongation Termination

20. Initiation Initiator tRNA binds to small ribosomal subunit Small subunit/tRNA complex attaches to mRNA and moves along it to an AUG “start” codon Large ribosomal subunit joins complex

21. Binding Sites on Large Subunit binding site for mRNA P (first binding site for tRNA) A (second binding site for tRNA)

22. Elongation mRNA passes through ribosomal subunits tRNAs deliver amino acids to the ribosomal binding site in the order specified by the mRNA Peptide bonds form between the amino acids and the polypeptide chain grows

23. Elongation

24. Termination A STOP codon moves into the area where the chain is being built. It is the signal to release the mRNA transcript from the ribosome. The new polypeptide chain is released from the ribosome. It is free to join the pool of proteins in the cytoplasm or to enter rough ER of the endomembrane system. The two ribosomal subunits now separate also.

25. Polysome - a lot of ribosomes A cluster of many ribosomes translating one mRNA transcript Transcript threads through the multiple ribosomes like the thread of bead necklace Why? - Allows rapid synthesis of proteins

26. What Happens to the New Polypeptides (proteins)? Some just enter the cytoplasm Many enter the endoplasmic reticulum and move through the cytomembrane system where they are modified

27. Overview

28. Gene Mutations Base-Pair Substitutions (small) Insertions (small or large) Deletions (small or large)

29. Frameshift Mutations Insertion –Extra base added into gene region Deletion –Base removed from gene region Both shift the reading frame Result in many wrong amino acids

30. Mutations in Genes - example of substitution & deletion

31. Transposons - naughty things! DNA segments that move spontaneously about the genome When they insert into a gene region, they usually inactivate that gene

32. Mutation Rates Each gene has a characteristic mutation rate Average rate for eukaryotes is between 10 -4 and 10 -6 per gene per generation Only mutations that arise in germ cells can be passed on to next generation

33. Causes of Mutations Exposure to harmful radiation and chemicals in the environment can cause DNA mutations Genetic defects to genes that repair mutations leave mutations behind in large numbers.