From DNA to Proteins

1. From DNA to Proteins

3. Occurs in the nucleus Occurs in the cytoplasm transcription translation DNA RNA PROTEINS Proteins are coded for by Genes- long stretches of DNA that code for a particular amino acid sequence in-text, p. 201

6. Steps from DNA to Proteins Same two steps produce ALL proteins: Example: insulin from pancreas 1) DNA is transcribed to form RNA • Occurs in the nucleus • mRNA moves into cytoplasm 2) RNA is translated to form polypeptide chains, which fold to form proteins

8. Three Classes of RNAs • Messenger RNA • Carries protein-building instruction • Ribosomal RNA • Major component of ribosomes • Transfer RNA • Delivers amino acids to ribosomes

9. A Nucleotide Subunit of RNA uracil (base) phosphate group sugar (ribose)

10. Base Pairing During Transcription • A new RNA strand can be put together on a DNA region according to base-pairing rules (What enzyme?) • As in DNA: C pairs with G • Uracil (U) pairs with adenine (A)

11. The Promoter • 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 Terminator

12. Gene Transcription mRNA transcript Where is the promoter?

13. Adding Nucleotides 5’ 3’ growing RNA transcript 5’ 3’ direction of transcription

14. snipped out snipped out Transcript Modification unit of transcription in a DNA strand 3’ 5’ exon intron exon intron exon transcription into pre-mRNA poly-A tail cap 5’ 3’ 5’ 3’ mature mRNA transcript

15. Code Is Redundant • Twenty kinds of amino acids are specified by 61 codons • Most amino acids can be specified by more than one codon • Six codons specify leucine • UUA, UUG, CUU, CUC, CUA, CUG

16. tRNA Structure codon in mRNA anticodon in tRNA tRNA molecule’s attachment site for amino acid amino acid OH

17. Ribosomes tunnel small ribosomal subunit large ribosomal subunit intact ribosome

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 A (second binding site for tRNA) P (first 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 in the mRNA moves onto the ribosomal binding site • No tRNA has a corresponding anticodon • Proteins called release factors bind to the ribosome • mRNA and polypeptide are released

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

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

27. Transcription rRNA tRNA mRNA Mature mRNA transcripts ribosomal subunits mature tRNA Translation

28. Gene Mutations Base-Pair Substitutions Insertions Deletions

29. Effect of Base-Pair Substitution original base triplet in a DNA strand a base substitution within the triplet (red) As DNA is replicated, proofreading enzymes detect the mistake and make a substitution for it: POSSIBLE OUTCOMES: OR One DNA molecule carries the original, unmutated sequence The other DNA molecule carries a gene mutation

30. 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

31. Frameshift Mutation mRNA PARENTAL DNA amino acid sequence ARGININE GLYCINE TYROSINE TRYPTOPHAN ASPARAGINE altered mRNA BASE INSERTION altered amino acid sequence ARGININE GLYCINE LEUCINE LEUCINE GLUTAMATE