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Transcription & Translation

Transcription & Translation. Chapter 17 (in brief) Biology – Campbell • Reece. DNA… Four bases are adenine, guanine, cytosine & thymine Sugar is deoxyribose Is a double -stranded helix. RNA… Four bases are adenine, guanine, cytosine & uracil Sugar is ribose

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Transcription & Translation

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  1. Transcription & Translation Chapter 17 (in brief) Biology – Campbell • Reece

  2. DNA… Four bases are adenine, guanine, cytosine & thymine Sugar is deoxyribose Is a double-stranded helix RNA… Four bases are adenine, guanine, cytosine & uracil Sugar is ribose Is a single-stranded helix RNA vs. DNA

  3. 3 Types of RNA • Messenger RNA (mRNA) – carries the instructions for making the protein from the nucleus to the ribosomes • Ribosomal RNA (rRNA) – makes up a ribosome • Transfer RNA (tRNA) – carries the amino acids to the ribosomes

  4. Transcription • The process of making RNA from DNA • The DNA serves as a template for making the RNA • Similar base-pairing rules apply: • Cytosine still pairs with Guanine • But Adenine now pairs with Uracil

  5. Transcription: The Process • RNA polymerase pries the two strands of DNA apart and hooks together the RNA nucleotides • Moves 3’→5’ along the DNA template strand • Promoter – the DNA sequence where the RNA polymerase attaches to begin transcription • Terminator – the sequence that signals the end of transcription

  6. Transcription: The Process

  7. 3 steps to Transcription • Initiation – the RNA polymerase binds to the promoter, DNA unwinds, RNA synthesis begins • Elongation – the polymerase moves along the DNA, elongating the RNA • Termination – the polymerase reaches the terminator, transcription stops, the RNA is released, polymerase detaches

  8. Introns and Exons • Introns are noncoding regions of DNA or RNA • Introns are “in the way” or are intervening and must be removed (RNA splicing) • Exons are the coded regions that are expressed

  9. Translation • The process of making the protein from the instructions on the mRNA • Occurs in the ribosomes • Codon – a sequence of 3 bases that codes for a specific amino acid • Anticodon – the complementary 3 base sequence on a tRNA molecule

  10. Codons & Anticodons

  11. Transcription: The Process • Initiation – the mRNA attaches to the ribosome, the tRNA brings the first amino acid • Elongation • 1) codon recognition • 2) peptide bond formation • 3) translocation

  12. Elongation

  13. Transcription: The Process • Termination – when a stop codon is reached, the polypeptide detaches, the mRNA leaves • Stop codons – UGA, UUA, UAG

  14. Substitution • An incorrect base is substituted for a correct one • Can result in no effect, missense or nonsense

  15. Insertion or Deletion • An extra nucleotide is added or one is missing • Results in frameshifts that can cause missense, nonsense, an extra amino acid, or a missing amino acid

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