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Necessary Components for Translation 1. Messenger RNA (mRNA): • Encodes for a specific protein sequence. • Variable length (depending on protein size). • Information is read in triplets (codons) 64 possible codons (4 x 4 x 4 = 64 = 43) 61 codons specify amino acids 3 codons are termination signals. mRNA is complementary to DNA and read in triplets (codons) Necessary Components for Translation 2. Transfer RNA (tRNA): • Brings one amino acid at a time to the growing polypeptide chain. • Small molecule (70 to 90 nucleotides). • Forms a cloverleaf structure. • Anticodon: Base pairs to mRNA codon during translation. • Amino acid binding site: At 3’ end of molecule. Transfer RNA (tRNA) Carries Amino Acids to the Growing Polypeptide Chain Necessary Components for Translation 3. Ribosomal RNA (rRNA): • Ribosome is the site of protein synthesis. • Facilitates coupling of mRNA to tRNA. • Huge molecule: Large and small subunits must assemble for translation. • Ribosome composition: 60% rRNA and 40% protein • Transfer RNA (tRNA) Carries Amino Acids to the Growing Polypeptide Chain Ribosome is the Site of Translation STEPS OF TRANSLATION 1. INITIATION: Messenger RNA (mRNA) and ribosome come together.Transfer RNA (tRNA): Carrying first amino acid (methionine) has anticodon which binds to start codon (AUG). 2. ELONGATION One amino acid at time is added and linked to growing polypeptide chain by a peptide bond. 3. TERMINATION-Stop codons: UAA, UAG, or UGA Ribosome/mRNA complex dissociates. Translation: Initiation at Start Codon Translation: During Elongation one Amino Acid is Added at a Time Elongation: Ribosome Travels Down mRNA, Adding One Amino Acid at a Time Termination: Once Stop Codon is Reached, Complex Disassembles Mutations • DNA replication is never 100% accurate. • Bases may be inserted, deleted, or mismatched during replication. • Mutations: are permanent changes in DNA. • Any mistakes that cause changes in the nucleotide sequence of DNA. • Mutations may be either harmful, beneficial, or have no effect on a cell or individual. Mutations There are several possible types of mutations: I. Substitution mutation: One nucleotide is replaced by another. May result in: 1. Missense: Different amino acid. May or may not have serious consequences. Example: Sickle cell anemia. 2. Nonsense: Stop codon. Protein is truncated. Usually has serious consequences. 3. Silent: No change in amino acid. No consequence. Missense Mutation in Sickle Cell Anemia Base substitution results in a single amino acid change Glu ---> Val Mutations • 2. Frameshift Mutation: Nucleotides which are inserted or deleted may change the gene’s reading frame. Usually serious, because entire protein sequence after mutation may be disrupted. Effects of Different Types of Mutations