Chapter 13.2 (Pgs. 366-371): Ribosomes and Protein Synthesis

The Genetic Code A gene is a section of DNA that codes for a trait, usually a protein This code specifies the order of amino acids in a protein This code is made of 3-letter “words” called codons Codons in mRNA have 3 RNA nucleotides (A, C, G or U) Each codon stands for an amino acid

Protein Synthesis Is also called translation Occurs in the cytoplasm Is the process of assembling a protein using the sequence of codons in mRNA Also requires ribosomes and tRNA Ribosomes help bond amino acids together tRNA has anticodons that are complementary to mRNA codons

Steps in Translation A ribosome attaches to mRNA molecule, and begins reading the mRNA at the “start” codon tRNA brings in an amino acid that matches the mRNA codon The ribosome helps amino acids bond to each other, and moves the growing polypeptide over to make room for the next amino acid When the ribosome reaches a “stop” codon, it releases the mRNA and the protein

The Central Dogma of Molecular Biology Information is transferred from DNA to RNA to protein DNA -> RNA -> Protein Proteins create traits This is called gene expression This process is found in all organisms

Differences in Transcription and Translation Occurs in the nucleus Makes RNA Uses DNA as a template Uses RNA polymerase Uses RNA nucleotides as the building blocks Occurs in the cytoplasm Makes a protein Uses mRNA as a template Uses ribosomes and tRNA Uses amino acids as the building blocks