protein synthesis n.
Skip this Video
Loading SlideShow in 5 Seconds..
PROTEIN SYNTHESIS PowerPoint Presentation
Download Presentation


127 Vues Download Presentation
Télécharger la présentation


- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript


  2. Protein Synthesis • The production (synthesis) of polypeptide chains (proteins) • Two phases:Transcription & Translation • mRNA must be processed before it leaves the nucleus of eukaryotic cells

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

  4. Nuclear membrane DNA Transcription Pre-mRNA RNA Processing mRNA Ribosome Translation Protein DNA  RNA Protein 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 • The code is nearly universal among living organisms

  14. Transcription Translation

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

  16. Steps in 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 promoter DNA (TATA box) • Ends at terminator DNA (stop) • When complete, pre-RNA molecule is released

  17. Transcription

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

  19. RNA Polymerase • Enzyme found in the nucleus • Separates the two DNA strands by breaking the hydrogen bonds between the bases • Then moves along one of the DNA strands and links RNA nucleotides together

  20. DNA RNA Polymerase pre-mRNA

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

  22. 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

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

  24. Messenger RNA (mRNA) • Carries the information for a specific protein • Made up of 500 to 1000 nucleotides long • Sequence of 3 bases called codon • AUG – methionine or start codon • UAA, UAG, or UGA – stop codons

  25. 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)

  26. Transfer RNA (tRNA) • Made up of 75 to 80 nucleotides long • Picks up the appropriate amino acidfloating in the cytoplasm • Transports amino acidsto the mRNA • Have anticodons that are complementary to mRNA codons • Recognizes the appropriate codons on the mRNA and bonds to them with H-bonds

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

  28. Ribosomal RNA (rRNA) • Made up of rRNA is 100 to 3000 nucleotides long • Made inside the nucleus of a cell • Associates with proteins to form ribosomes

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

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

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

  32. 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 !

  33. mRNA A U G C U A C U U C G mRNA Codons Join the Ribosome Large subunit P Site A Site Small subunit

  34. 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

  35. 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

  36. 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

  37. 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

  38. 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

  39. aa5 5-tRNA U 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 A C U mRNA

  40. 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

  41. 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

  42. 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