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Chapter 14

Chapter 14. RNA and Protein Synthesis. RNA: Structure and Function. Types of RNA Cells have three major types of RNA: messenger RNA (mRNA): carries the genetic message from nucleus to cytoplasm ribosomal RNA ( rRNA ): component of ribosomes

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Chapter 14

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  1. Chapter 14 RNA and Protein Synthesis

  2. RNA: Structure and Function • Types of RNA • Cells have three major types of RNA: • messenger RNA(mRNA): carries the genetic message from nucleus to cytoplasm • ribosomal RNA (rRNA): component of ribosomes • transfer RNA (tRNA): carries amino acids to add to a growing polypeptide (protein) chain

  3. Messenger RNA (mRNA) • Single, uncoiled, straight strand of nucleic acid • Copies DNA’s instructions in nucleus & carries them to the ribosomes in cytoplasm where proteins can be made • mRNA’s base sequence is translated into the amino acid sequence of a protein • Three consecutive bases on mRNA called a codon (e.g. UAA, CGC, AGU) • Reusable

  4. Ribosomal RNA (rRNA) • rRNA & protein make up the large and small subunits of ribosomes • Globular shape • Ribosomes are the sites of translation (the making of proteins)

  5. Transfer RNA (tRNA) • Clover-leaf shape (folds up) • Single stranded molecule with attachment site at one end for an amino acid • Opposite end has three nucleotide bases called the anticodon • Anticodon will be complementary to the codons of the mRNA

  6. Nuclear membrane DNA Transcription Pre-mRNA RNA Processing mRNA Ribosome Translation Protein The Central Dogma of Biology DNA mRNA  Protein

  7. Transcription Translation

  8. TRANSCRIPTION DNA mRNA

  9. Transcription • During transcription, DNA acts as a template for directing the synthesis of mRNA • Happens IN THE NUCLEUS (know this!) Transcription: the copying of the DNA into a complementary strand of RNA - Uses the enzyme RNA polymerase

  10. Transcription: Step 1 • RNA polymerase, an enzyme,binds to a region of DNA known as the promoter • The promoteris a sequence of DNA that tells transcription where to begin

  11. Transcription: Step 2 • Multiple enzymes unwind and separate the two DNA strands • The RNA polymerase will use oneof the DNA strands as a template from which to build a strand of RNA (the mRNA)

  12. Transcription: Step 3 • Using one of the DNA strands as a template, RNA polymerase adds nucleotides that are complementary to the DNA strand • G with C, and U with A • This continues until RNA polymerase reaches a DNA sequence known as the terminator/termination signal • RNA polymerase falls off, and the newly-formed mRNA strand is released

  13. Transcription Summary https://www.youtube.com/watch?v=5MfSYnItYvg&app=desktop

  14. Eukaryotic RNA is Modified • Before leaving the nucleus, the mRNA is edited • This is called splicing • Splicing involves removing (cutting out) portions of the mRNA known as introns • The exons are fused together • One end of the mRNA also receives a poly-A tail, and the other end receives a 5’ cap (bases and chemical groups to prevent mRNA destruction) Remember it this way: the “exons” get to “exit” the nucleus and be translated into proteins! The introns stay “in” the nucleus.

  15. TRANSLATION mRNA  Protein

  16. Translation • Translation is the process of decoding the mRNA into a polypeptide chain (protein) The Genetic Code The genetic code is read in three letter segments called codons There are 64 different codon possibilities that code for only 20 amino acids -AUG is the start codon -there are 3 stop codons- UAA, UAG, UGA

  17. Translation: Step 1 (Initiation) Start codon • mRNAtravels from the nucleus to the cytoplasm • mRNA attaches to one end of a ribosome; calledinitiation • tRNAs attach the correct amino acid floating in the cytoplasm to themselves • The tRNA anticodon “reads”& temporarily attaches to the mRNA codon in the ribosome (methionine is the start codon)

  18. Translation: Step 2 (Elongation) • 5. Two amino acids at a time are linkedtogether by peptide bonds to make polypeptide chains (protein subunits); called elongation

  19. Translation: Step 2 (Elongation), cont. Growing polypeptide chain

  20. Translation: Step 3 (Termination) • 7. Ribosomes move along the mRNAstrand until they reach a stop codon (UAA, UGA, or UAG);calledtermination 8. tRNA’s break loose from amino acid, leave the ribosome, & return to cytoplasm to pick up another amino acid https://www.youtube.com/watch?v=8dsTvBaUMvw&app=desktop

  21. End Product –The Protein! • The end product of protein synthesis is a primary structureof a protein • A sequence of amino acids bonded together by peptide bonds

  22. End Product –The Protein! • The linear, primary structure will fold up into a functional protein • Once the protein is properly folded into a tertiary or quaternary structure, it can perform its job! • STRUCTURE = FUNCTION https://www.youtube.com/watch?v=gG7uCskUOrA&app=desktop

  23. Example: How Mutations Affect Protein Structure and Function Sickle-Cell Anemia

  24. Example: How Mutations Affect Protein Structure and Function Cystic Fibrosis • The thick build-up of mucus occurs in the lungs, which affects breathing and can cause recurring respiratory infections • Mucus build-up also occurs in the pancreas, which prevents the normal secretion of necessary digestive enzymes. This can lead to digestive problems and poor growth/development. (Many CF patients are prescribed pancreatic enzymes)

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