Protein Syntheis


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Simple version of protein synthesis

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Protein Syntheis

  1. 1. PROTEIN SYNTHESIS <ul><li>The formation of new proteins using the code carried on DNA </li></ul>
  2. 2. Gene is Selected <ul><li>A gene is a section of DNA coding for a particular polypeptide or protein. </li></ul><ul><li>When a protein is required by the cell or the organism as a whole, the gene for that protein is activated. </li></ul>Gene
  3. 3. Introns and Exons <ul><li>DNA is made up of coding sequences called exons and non coding sequences called introns . </li></ul>Exon Exon Exon Exon Intron Intron Intron Intron
  4. 4. Transcription <ul><li>An enzyme RNA Polymerase unwinds the section of DNA carrying the desired gene. </li></ul><ul><li>Only one strand of the DNA (the template) is recognised. </li></ul><ul><li>RNA Polymerase then binds to a promoter site and begins to form an RNA copy of the template strand (called messenger RNA (mRNA)). </li></ul>
  5. 5. Naming the Strands <ul><li>An mRNA copy of the top coding strand is made by base pairing with the bottom template strand . </li></ul>DNA Primary RNA Coding strand Template strand <ul><li>The DNA strand is unwound exposing the bases that carry the genetic code. </li></ul>
  6. 6. Messenger RNA <ul><li>Free nucleotides match up with the coded sequence of DNA. </li></ul><ul><li>When bases pair, Uracil is present in RNA instead of Thymine . </li></ul><ul><li>A single stranded primary transcript that is complementary to the template strand is formed. </li></ul><ul><li>DNA template TAC GCC AAA TCC </li></ul><ul><li>mRNA codons AUG CGG UUU AGG </li></ul>
  7. 7. Removal of Introns <ul><li>The primary transcript contains a copy of both introns and exons. </li></ul><ul><li>Introns are removed and exons are spliced (joined) to form mature mRNA. </li></ul>
  8. 8. Movement of mRNA <ul><li>The completed single strand of mRNA migrates out of the nucleus through pores in the nuclear membrane. </li></ul><ul><li>mRNA binds to ribosomes. </li></ul><ul><li>The mRNA is divided into triplets of bases called codons . </li></ul><ul><li>Different codons carry the code for a particular amino acid (AA) </li></ul><ul><li>Other codons carry start and stop codes. </li></ul>
  9. 9. Important Codon Facts <ul><li>AUG is the start codon on all viable mRNA molecules. It also codes for the amino acid Methionine. </li></ul><ul><li>UAA, UAG, UGA are stop codes. </li></ul><ul><li>Many codons are degenerate --more than one codon codes for an AA. </li></ul><ul><li>The code is universal . The same codes work in all organisms. </li></ul><ul><li>4 3 different combinations give 64 different codons. </li></ul>
  10. 10. Amino Acid Codons
  11. 11. Transfer RNA <ul><li>Transfer RNA (tRNA) is a carrier molecule which picks up amino acids from the cytoplasm and carries them to the mRNA / ribosome complex. </li></ul>anticodon U A C
  12. 12. Translation <ul><li>A triplet of bases on the tRNA called an anticodon matches with the mRNA codon. </li></ul><ul><li>tRNA carrying its AA binds to the codon </li></ul><ul><li>The ribosome moves along the mRNA activating new codons. </li></ul><ul><li>AA’s are joined by peptide bonds to form long polypeptide chains. </li></ul>
  13. 13. Ribosome Action <ul><li>The ribosome acts as catalyst holding all the components together while bonds are formed. </li></ul>A U G C G G U U U A G G C C C U A G G C C AA 2 U A C AA 1
  14. 14. Peptide Bond Formation <ul><li>As the ribosome moves along the mRNA, amino acids are added until a stop signal is reached. </li></ul>A U G C G G U U U A G G C C C U A G A U C stop AA 1 AA 4 AA 3 AA 2 AA 5
  15. 15. Translation speed <ul><li>Rapid protein formation can be achieved when the mRNA is attached to more than one ribosome. </li></ul>
  16. 16. Electron Microscope View <ul><li>mRNA (purple) binds to a ribosome. </li></ul><ul><li>Beads of AA’s (yellow) are joined to form a polypeptide. </li></ul>
  17. 17. Questions <ul><li>What name is given to a section of DNA coding for a polypeptide? </li></ul><ul><li>Gene. </li></ul><ul><li>The coding sequences of DNA are known as what? </li></ul><ul><li>Exons. </li></ul><ul><li>Name the enzyme responsible for unwinding the DNA helix. </li></ul><ul><li>RNA Polymerase. </li></ul><ul><li>How does the enzyme recognize the start of a message? </li></ul><ul><li>It binds to a promoter site. </li></ul><ul><li>Which DNA strand is used in the base pairing process? </li></ul><ul><li>The template. </li></ul>
  18. 18. <ul><li>What name is given to the RNA strand first formed, that contains introns and exons? </li></ul><ul><li>Primary transcript. </li></ul><ul><li>In RNA, which base binds with Adenine? </li></ul><ul><li>Uracil. </li></ul><ul><li>What is the codon for the start of an mRNA? </li></ul><ul><li>AUG. </li></ul><ul><li>What are the three stop codons? </li></ul><ul><li>UAA, UAG, UGA. </li></ul><ul><li>What does the term “codons are degenerate” mean? </li></ul><ul><li>More than one codon may code for an amino acid. </li></ul><ul><li>Why is the codon a three base sequence? </li></ul><ul><li>4 3 different combinations gives codes for all 20 amino acids, start and stop codes plus degenerate codes. </li></ul>
  19. 19. <ul><li>What does the term, “the genetic code is universal” mean? </li></ul><ul><li>The same code works in all organisms. </li></ul><ul><li>What name is given to the process of forming mRNA? </li></ul><ul><li>Transcription. </li></ul><ul><li>What is the full name for tRNA? </li></ul><ul><li>Transfer Ribonucleic acid. </li></ul><ul><li>What is the role of tRNA? </li></ul><ul><li>Carries amino acids from the cytoplasm to the ribosomes. </li></ul><ul><li>mRNA has a codon, tRNA has an? </li></ul><ul><li>Anticodon. </li></ul><ul><li>What holds amino acids together in a polypeptide? </li></ul><ul><li>Peptide bonds. </li></ul>
  20. 20. <ul><li>What is the role of the ribosomes? </li></ul><ul><li>They act as catalysts, holding the various components together. </li></ul><ul><li>How do the ribosomes operate that allows long amino acid chains to form? </li></ul><ul><li>They move along the mRNA allowing tRNA’s to bring in new amino acids. </li></ul><ul><li>What name is given to the process of converting an mRNA code into an amino acid sequence? </li></ul><ul><li>Translation. </li></ul><ul><li>Describe one way in which the rate of translation can be increased? </li></ul><ul><li>By attaching the mRNA to more than one ribosome. </li></ul>