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PROTEIN SYNTHESIS

PROTEIN SYNTHESIS. Protein Synthesis. The production (synthesis) of proteins . 3 phases : 1. Transcription 2. RNA processing 3. Translation Remember: DNA  RNA  Protein. Nuclear membrane. DNA. Transcription. Pre-mRNA. RNA Processing. mRNA. Ribosome. Translation. Protein.

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PROTEIN SYNTHESIS

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  1. PROTEIN SYNTHESIS

  2. Protein Synthesis • The production (synthesis) of proteins. • 3 phases: 1. Transcription 2. RNA processing 3. Translation • Remember: DNA  RNA  Protein

  3. Nuclear membrane DNA Transcription Pre-mRNA RNA Processing mRNA Ribosome Translation Protein DNA  RNA Protein Eukaryotic Cell

  4. DNA Transcription mRNA Ribosome Translation Protein DNA  RNA Protein Prokaryotic Cell

  5. Question: • How does RNA(ribonucleic acid) differ from DNA (deoxyribonucleic acid)?

  6. RNA differs from DNA 1. RNA has a sugar ribose DNA has a sugar deoxyribose 2. RNA contains uracil (U) DNA has thymine (T) 3. RNA molecule is single-stranded DNA is double-stranded

  7. Nuclear membrane DNA Transcription Pre-mRNA RNA Processing mRNA Ribosome Translation Protein 1. Transcription Eukaryotic Cell

  8. 1. Transcription • The transfer of information in the nucleus from a DNA molecule to an RNA molecule. • Only 1 DNA strand serves as the template • Starts at promoterDNA (TATA box) • Ends at terminatorDNA (stop) • When complete, pre-RNA molecule is released.

  9. Question: • What enzymes are responsible for the production of the RNA molecule?

  10. Answer: Helicase and RNA Polymerase • Helicase separates the DNA molecule by breaking the H-bonds between the bases. • RNA Polymerase moves along one of the DNA strands and links RNA nucleotides together.

  11. DNA RNA Polymerase pre-mRNA 1. Transcription

  12. Question: • What would be the complementary RNA strand for the following DNA sequence? • DNA 5’-GCGTATG-3’

  13. Answer: • DNA 5’-GCGTATG-3’ • RNA 3’-CGCAUAC-5’

  14. Nuclear membrane DNA Transcription Pre-mRNA RNA Processing mRNA Ribosome Translation Protein 2. RNA Processing Eukaryotic Cell

  15. 2. RNA Processing • Maturation of pre-RNA molecules. • Also occurs in the nucleus. • Introns spliced out by splicesome-enzyme and exonscome together. • End product is a messenger RNA molecule (mRNA) that leaves the nucleus to the cytoplasm.

  16. pre-RNA molecule exon intron exon exon intron intron intron exon exon exon splicesome splicesome exon exon exon Messenger RNA molecule 2. RNA Processing

  17. Types of RNA • Three types ofRNA: A. messenger RNA (mRNA) B. transfer RNA (tRNA) C. ribosomal RNA (rRNA) • Remember: all produced in thenucleus!

  18. A. Messenger RNA (mRNA) • Carries the information for a specific protein. • Made up of 500 to 1000 nucleotides long. • Made up of codons (sequence of three bases: AUG - methionine). • Each codon, is specific for an amino acid.

  19. start codon A U G G G C U C C A U C G G C G C A U A A mRNA codon 1 codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 stop codon protein methionine glycine serine isoleucine glycine alanine Primary structure of a protein aa2 aa3 aa4 aa5 aa6 aa1 peptide bonds A. Messenger RNA (mRNA)

  20. B. Transfer RNA (tRNA) • Made up of 75 to 80 nucleotides long. • Picks up the appropriate amino acid floating in the cytoplasm (amino acid activating enzyme) • Transports amino acids to the mRNA. • Have anticodons that are complementary to mRNAcodons. • Recognizes the appropriate codons on the mRNA and bonds to them with H-bonds.

  21. amino acid attachment site methionine amino acid U A C anticodon B. Transfer RNA (tRNA)

  22. C. Ribosomal RNA (rRNA) • Made up of rRNA is 100 to 3000 nucleotides long. • Important structural component of a ribosome. • Associates with proteins to form ribosomes.

  23. Ribosomes • Large and small subunits. • Composed of rRNA (40%) and proteins (60%). • Both units come together and help bind the mRNA and tRNA. • Two sites fortRNA a. P site(first and last tRNA will attach) b. A site

  24. mRNA A U G C U A C U U C G Ribosomes Large subunit P Site A Site Small subunit

  25. Nuclear membrane DNA Transcription Pre-mRNA RNA Processing mRNA Ribosome Translation Protein 3. Translation Eukaryotic Cell

  26. 3. Translation • Synthesis of proteins in the cytoplasm • Involves the following: 1. mRNA (codons) 2. tRNA (anticodons) 3. rRNA 4. ribosomes 5. amino acids

  27. 3. Translation • Three parts: 1. initiation: start codon (AUG) 2. elongation: 3. termination: stop codon (UAG) • Let’s make a PROTEIN!!!!.

  28. mRNA Codon Translation Table

  29. mRNA A U G C U A C U U C G 3. Translation Large subunit P Site A Site Small subunit

  30. aa2 aa1 2-tRNA 1-tRNA G A U U A C Initiation anticodon A U G C U A C U U C G A hydrogen bonds codon mRNA

  31. aa3 3-tRNA G A A Elongation peptide bond aa1 aa2 1-tRNA 2-tRNA anticodon U A C G A U A U G C U A C U U C G A hydrogen bonds codon mRNA

  32. aa3 3-tRNA G A A aa1 peptide bond aa2 1-tRNA U A C (leaves) 2-tRNA G A U A U G C U A C U U C G A mRNA Ribosomes move over one codon

  33. aa4 4-tRNA G C U peptide bonds aa1 aa2 aa3 2-tRNA 3-tRNA G A U G A A A U G C U A C U U C G A A C U mRNA

  34. aa4 4-tRNA G C U peptide bonds aa1 aa2 aa3 2-tRNA G A U (leaves) 3-tRNA G A A A U G C U A C U U C G A A C U mRNA Ribosomes move over one codon

  35. aa5 5-tRNA G G A peptide bonds aa1 aa2 aa4 aa3 3-tRNA 4-tRNA G A A G C U G C U A C U U C G A C C U mRNA

  36. aa5 5-tRNA G G A peptide bonds aa1 aa2 aa3 aa4 3-tRNA G A A 4-tRNA G C U G C U A C U U C G A C C U mRNA Ribosomes move over one codon

  37. aa5 aa4 Termination aa199 aa200 aa3 primary structure of a protein aa2 aa1 terminator or stop codon 200-tRNA C C U C A U G U U U A G mRNA

  38. aa5 aa4 aa3 aa2 aa199 aa1 aa200 End Product • The end products of protein synthesis is a primary structure of a protein. • A sequence of amino acid bonded together by peptide bonds.

  39. Question: • The anticodon UAC belongs to a tRNA that recognizes and binds to a particular amino acid. • What would be the DNA base code for this amino acid?

  40. Answer: • tRNA - UAC (anticodon) • mRNA - AUG (codon) • DNA - TAC

  41. When things go wrong… • Mutations: changes in the DNA sequence, that may be passed along to future generations. • Point mutations: a single base substitution THE CAT SAW THE RAT THE CAT SAW THE HAT • Deletion: a small DNA segment is lost THE CAT SAW THE RAT THE ATS AWT HER AT • Insertion: a segment of DNA is added THE CAT SAW THE HAT THE CAT SAW THE BHAT

  42. Mutations • Frame-shift mutation: modification of the reading frame after a deletion or insertion, resulting in all codons downstreams being different. For example: THE RAT SAW THE CAT AND RAN If you take out the “R” in “RAT” and shift the frames, you get: THE ATS AWT HEC ATA NDR AN The resulting sentence (or mRNA message) is meaningless!

  43. Mutations • Somatic mutations: occur in body cells, or cells that do not lead to gametes. • Somatic mutations that occur in leaves, roots or stems are usually not passed on to future generations… UNLESS the plant is reproduced asexually.

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