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PROTEIN SYNTHESIS Protein Synthesis • The production (synthesis) of proteins. • 3 phases: 1. Transcription 2. RNA processing 3. Translation • Remember: DNA RNA Protein DNA RNA Protein Nuclear membrane DNA Transcription Eukaryotic Cell Pre-mRNA RNA Processing mRNA Ribosome Translation Protein DNA RNA Protein DNA Transcription mRNA Ribosome Translation Protein Prokaryotic Cell Question: • How does RNA (ribonucleic acid) differ from DNA (deoxyribonucleic acid)? RNA differs from DNA 1. RNA has a sugar ribose DNA has a sugar deoxyribose 2. RNA contains uracil (U) DNA has thymine (T) 3. RNA molecule is single-stranded DNA is double-stranded 1. Transcription Nuclear membrane DNA Transcription Eukaryotic Cell Pre-mRNA RNA Processing mRNA Ribosome Translation Protein 1. Transcription • The transfer of information in the nucleus from a DNA molecule to an RNA molecule. • Only 1 DNA strand serves as the template • Starts at promoter DNA (TATA box) • Ends at terminator DNA (stop) • When complete, pre-RNA molecule is released. Question: • What enzymes are responsible for the production of the RNA molecule? Answer: Helicase and RNA Polymerase • Helicase separates the DNA molecule by breaking the H-bonds between the bases. • RNA Polymerase moves along one of the DNA strands and links RNA nucleotides together. 1. Transcription DNA RNA Polymerase pre-mRNA Question: • What would be the complementary RNA strand for the following DNA sequence? • DNA 5’-GCGTATG-3’ Answer: • DNA 5’-GCGTATG-3’ • RNA 3’-CGCAUAC-5’ 2. RNA Processing Nuclear membrane DNA Transcription Eukaryotic Cell Pre-mRNA RNA Processing mRNA Ribosome Translation Protein 2. RNA Processing • Maturation of pre-RNA molecules. • Also occurs in the nucleus. • Introns spliced out by splicesome-enzyme and exons come together. • End product is a messenger RNA molecule (mRNA) that leaves the nucleus to the cytoplasm. 2. RNA Processing pre-RNA molecule exon intron exon intron exon intron intron exon splicesome exon exon splicesome exon exon exo n Messenger RNA molecule Types of RNA • Three types of RNA: A. messenger RNA (mRNA) B. transfer RNA (tRNA) C. ribosomal RNA (rRNA) • Remember: all produced in the nucleus! A. Messenger RNA (mRNA) • Carries the information for a specific protein. • Made up of 500 to 1000 nucleotides long. • Made up of codons (sequence of three bases: AUG - methionine). • Each codon, is specific for an amino acid. A. Messenger RNA (mRNA) start codon mRNA A U G G G C U C C A U C G G C G C A U A A codon 1 protein methionine codon 2 codon 3 glycine serine codon 4 isoleucine codon 5 codon 6 glycine alanine codon 7 stop codon Primary structure of a protein aa1 aa2 aa3 peptide bonds aa4 aa5 aa6 B. Transfer RNA (tRNA) • Made up of 75 to 80 nucleotides long. • Picks up the appropriate amino acid floating in the cytoplasm (amino acid activating enzyme) • Transports amino acids to the mRNA. • Have anticodons that are complementary to mRNA codons. • Recognizes the appropriate codons on the mRNA and bonds to them with H-bonds. B. Transfer RNA (tRNA) amino acid attachment site methionine U A C anticodon amino acid C. Ribosomal RNA (rRNA) • Made up of rRNA is 100 to 3000 nucleotides long. • Important structural component of a ribosome. • Associates with proteins to form ribosomes. Ribosomes • Large and small subunits. • Composed of rRNA (40%) and proteins (60%). • Both units come together and help bind the mRNA and tRNA. • Two sites for tRNA a. P site (first and last tRNA will attach) b. A site Ribosomes Large subunit P Site A Site mRNA A U G Small subunit C U A C U U C G 3. Translation Nuclear membrane DNA Transcription Eukaryotic Cell Pre-mRNA RNA Processing mRNA Ribosome Translation Protein 3. Translation • Synthesis of proteins in the cytoplasm • Involves the following: 1. mRNA (codons) 2. tRNA (anticodons) 3. rRNA 4. ribosomes 5. amino acids 3. Translation • Three parts: 1. initiation: start codon (AUG) 2. elongation: 3. termination: stop codon (UAG) • Let’s make a PROTEIN!!!!. mRNA Codon Translation Table 3. Translation Large subunit P Site A Site mRNA A U G Small subunit C U A C U U C G Initiation aa1 aa2 2-tRNA 1-tRNA anticodon hydrogen bonds U A C A U G codon G A U C U A C U U C G A mRNA Elongation peptide bond aa3 aa1 aa2 3-tRNA 1-tRNA anticodon hydrogen bonds U A C A U G codon 2-tRNA G A A G A U C U A C U U C G A mRNA aa1 peptide bond aa3 aa2 1-tRNA 3-tRNA U A C (leaves) 2-tRNA A U G G A A G A U C U A C U U C G A mRNA Ribosomes move over one codon aa1 peptide bonds aa4 aa2 aa3 4-tRNA 2-tRNA A U G 3-tRNA G C U G A U G A A C U A C U U C G A A C U mRNA aa1 peptide bonds aa4 aa2 aa3 2-tRNA 4-tRNA G A U (leaves) 3-tRNA A U G G C U G A A C U A C U U C G A A C U mRNA Ribosomes move over one codon aa1 peptide bonds aa5 aa2 aa3 aa4 5-tRNA G G A 3-tRNA 4-tRNA G A A G C U G C U A C U U C G A C C U mRNA peptide bonds aa1 aa5 aa2 aa3 aa4 5-tRNA G G A 3-tRNA G A A 4-tRNA G C U G C U A C U U C G A C C U mRNA Ribosomes move over one codon aa4 aa5 Termination aa199 aa3 primary structure aa2 of a protein aa200 aa1 200-tRNA C C U mRNA terminator or stop codon C A U G U U U A G End Product • The end products of protein synthesis is a primary structure of a protein. • A sequence of amino acid bonded together by peptide bonds. aa2 aa1 aa3 aa4 aa5 aa199 aa200 Question: • The anticodon UAC belongs to a tRNA that recognizes and binds to a particular amino acid. • What would be the DNA base code for this amino acid? Answer: • tRNA • mRNA • DNA - UAC (anticodon) - AUG (codon) - TAC When things go wrong… • Mutations: changes in the DNA sequence, that may be passed along to future generations. • Point mutations: a single base substitution THE CAT SAW THE RAT THE CAT SAW THE HAT • Deletion: a small DNA segment is lost THE CAT SAW THE RAT THE ATS AWT HER AT • Insertion: a segment of DNA is added THE CAT SAW THE HAT THE CAT SAW THE BHAT Mutations • Frame-shift mutation: modification of the reading frame after a deletion or insertion, resulting in all codons downstreams being different. For example: THE RAT SAW THE CAT AND RAN If you take out the “R” in “RAT” and shift the frames, you get: THE ATS AWT HEC ATA NDR AN The resulting sentence (or mRNA message) is meaningless! Mutations • Somatic mutations: occur in body cells, or cells that do not lead to gametes. • Somatic mutations that occur in leaves, roots or stems are usually not passed on to future generations… UNLESS the plant is reproduced asexually.