Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Transcription & Translation Chapter 17 (in brief) Biology – Campbell • Reece RNA vs. DNA DNA… – Four bases are adenine, guanine, cytosine & thymine – Sugar is deoxyribose – Is a doublestranded helix RNA… – Four bases are adenine, guanine, cytosine & uracil – Sugar is ribose – Is a singlestranded helix 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 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 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 Transcription: The Process 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 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 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 Codons & Anticodons 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 Elongation Transcription: The Process Termination – when a stop codon is reached, the polypeptide detaches, the mRNA leaves – Stop codons – UGA, UUA, UAG Substitution An incorrect base is substituted for a correct one Can result in no effect, missense or nonsense 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