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Protein Synthesis Traits are determined by proteins (often enzymes) *Protein – 1 or more polypeptide chains *Polypeptide – chain of amino acids linked by peptide bonds *One gene – one polypeptide (sort of) The “Central Dogma” of Biology DNA (replication) RNA Protein (transcription) (translation) *the concept is basically right but modern biology is leading to an understanding of much more complexity RNA Differs from DNA: 1. Sugar is ribose (has an OH off the 2’ carbon) 2. Uracil replaces thymine 3. Single stranded (usually) Types of RNA in protein synthesis 1. Messenger RNA (mRNA) -triplet codons, long strand 2. Transfer RNA (tRNA) -small (70-80 nucleotides) -about 45 different ones -carry amino acids to ribosome on board 3. Ribosomal RNA (rRNA) -together with proteins it makes up ribosomes -assembled in nucleolus -large and small subunits come together ribosomes Transcription 1. Initiation – RNA polymerase attaches to DNA at promoter region (beginning of gene – 3’ end) - unzips DNA strands 2. Elongation – RNA polymerase links RNA nucleotides -mRNA strand made 5’3’ 3. Termination – mRNA strand breaks off from DNA template RNA Splicing • mRNA is processed before it leaves nucleus -portions not necessary for polypeptide production are removed Intron – portion of gene that does not code for anything -removed by RNA splicing Exon – segments that contain the info The Genetic Code • Almost universal –strong evidence for common ancestry • Must be triplet: – 20 amino acids need at least 20 base combos – 4 bases (A,U,G,C) • 42 = 16 (No good!) • 43 = 64 combos (sufficient, and also allows for redundancy) Translation * mRNA is read, code is translated into polypeptide 1. Initiation – all of the below come together at 5’ end of mRNA at “start codon” (AUG) – small ribosome subunit – Large ribosome subunit – tRNA carrying methionine 2. Elongation -ribosome moves down mRNA a codon at a time -at each mRNA codon a tRNA (with complementary anticodon): -temporarily binds -leaves its amino acid behind -breaks off -the amino acids are linked as a polypeptide chain (by peptide bonds) 3. Termination -upon reaching a stop codon -ribosome units, mRNA, polypeptide separate