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PROTEIN SYNTHESIS

PROTEIN SYNTHESIS. Protein Synthesis. The production (synthesis) of polypeptide chains (proteins) Two phases: Transcription & Translation. DNA. Transcription. mRNA. Ribosome. Translation. Protein. DNA  RNA  Protein. Prokaryotic Cell. Nuclear membrane. DNA. Pre-mRNA.

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PROTEIN SYNTHESIS

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  1. PROTEIN SYNTHESIS

  2. Protein Synthesis • The production (synthesis) of polypeptide chains (proteins) • Two phases:Transcription& Translation

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

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

  5. Pathway to Making a Protein DNA mRNA tRNA (ribosomes) Protein

  6. RNA

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

  8. Structure of RNA

  9. Three Types of RNA . • Messenger RNA (mRNA) carries genetic information to the ribosomes • Ribosomal RNA (rRNA), along with protein, makes up the ribosomes • Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized

  10. Making a Protein

  11. Genes & Proteins • Proteins are made of amino acids linked together by peptide bonds • 20 different amino acids exist • Amino acids chains are called polypeptides • Segment of DNA that codes for the amino acid sequence in a protein are called genes

  12. Two Parts of Protein Synthesis • Transcription makes an RNA molecule complementary to a portion of DNA • Translationoccurs when the sequence of bases of mRNA DIRECTS the sequence of amino acids in a polypeptide

  13. Genetic Code • DNA contains a triplet code • Every three bases on DNA stands for ONE amino acid • Each three-letter unit on mRNA is called a codon • Most amino acids have more than one codon! • There are 20 amino acids with a possible 64 different triplets

  14. Transcription Translation

  15. Overview of Transcription • During transcription in the nucleus, a segment of DNA unwinds and unzips, and the DNAserves as atemplate for mRNA formation • RNA polymerase joins the RNA nucleotides so that the codons in mRNA are complementary to the triplet code in DNA

  16. What is the enzyme responsible for the production of the mRNA molecule?

  17. RNA Polymerase • RNA Polymerase is an Enzyme found in the nucleus • Moves along one of the DNA strands and links RNA nucleotides together at the same time DNA is being replicated

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

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

  20. Processing Pre-mRNA • Also occurs in the nucleus • Pre-mRNA made up of segments called introns & exons • Exons code for proteins, while introns do NOT! • Introns spliced out by splicesome-enzyme and exons re-join • End product is a mature RNA molecule that leaves the nucleus to the cytoplasm

  21. pre-RNA molecule exon exon exon intron intron intron intron exon exon exon splicesome splicesome exon exon exon Mature RNA molecule RNA Processing

  22. Messenger RNA (mRNA) • Carries the information for a specific protein • Sequence of 3 bases called codon • AUG – methionine or startcodon • UAA, UAG, or UGA – stopcodons

  23. 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 Messenger RNA (mRNA)

  24. Transfer RNA (tRNA) • Picks up the appropriate amino acid floating in the cytoplasm • Transports amino acids to the mRNA • Have anticodons that are complementary to mRNA codons • Recognizes the appropriate codonson the mRNA and bonds to them with H-bonds

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

  26. Ribosomal RNA (rRNA) • Made inside the nucleus of a cell • Associates with proteins to form ribosomes

  27. Ribosomes • Made of a large and small subunit • Composed of rRNA (40%) and proteins (60%) • Have two sites for tRNA attachment --- P and A

  28. mRNA A U G C U A C U U C G Ribosomes Large subunit P Site A Site Smallsubunit

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

  30. Translation • Three steps: 1. initiation: start codon (AUG) 2. elongation: amino acids linked 3. termination: stop codon (UAG, UAA, or UGA). Let’s Make a Protein !

  31. mRNA Codons Join the Ribosomes mRNA A U G C U A C U U C G Large subunit P Site A Site Smallsubunit 33

  32. 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

  33. 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

  34. 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

  35. aa4 4-tRNA G C U aa1 peptide bonds 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

  36. 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

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

  38. aa5 5-tRNA U 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 A C U mRNA Ribosomes move over one codon

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

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

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