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

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

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

Transcription The process of making RNA from DNA The process of making RNA from DNA The DNA serves as a template for making the RNA The DNA serves as a template for making the RNA Similar base-pairing rules apply: 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 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 Promoter – the DNA sequence where the RNA polymerase attaches to begin transcription Terminator – the sequence that signals the end of 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 Initiation – the RNA polymerase binds to the promoter, DNA unwinds, RNA synthesis begins Elongation – the polymerase moves along the DNA, elongating the RNA Elongation – the polymerase moves along the DNA, elongating the RNA Termination – the polymerase reaches the terminator, transcription stops, the RNA is released, polymerase detaches 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 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 Exons are the coded regions that are expressed

Translation The process of making the protein from the instructions on the mRNA The process of making the protein from the instructions on the mRNA Occurs in the ribosomes Occurs in the ribosomes Codon – a sequence of 3 bases that codes for a specific amino acid Codon – a sequence of 3 bases that codes for a specific amino acid Anticodon – the complementary 3 base sequence on a tRNA molecule 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 Initiation – the mRNA attaches to the ribosome, the tRNA brings the first amino acid Elongation 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 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 An incorrect base is substituted for a correct one Can result in no effect, missense or nonsense Can result in no effect, missense or nonsense

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