protein synthesis
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Protein Synthesis. 12-3. 2 Steps of Protein Synthesis. Transcription Translation. Transcription. DNA is coded (transcribed) into the RNA “language” The DNA sequence is copied into a complementary RNA sequence G C C G T A A U. Transcription. - PowerPoint PPT PresentationTRANSCRIPT
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Protein Synthesis
12-3
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2 Steps of Protein Synthesis•Transcription
•Translation
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Transcription• DNA is coded (transcribed) into
the RNA “language”
• The DNA sequence is copied into a complementary RNA sequenceG CC GT AA U
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Transcription• Transcription requires RNA polymerase, an
enzyme a lot like DNA polymerase
• RNA polymerase binds to DNA, separates the strands, and uses one strand as a template for making mRNA.
• RNA polymerase “polymerizes” (links together) the nucleotides that make up mRNA
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Where to Start?• RNA polymerase doesn’t randomly bind to DNA.
• It will only bind to sites known as promoters—regions of DNA that have specific sequences.
• Promoters are signals that say “START RNA HERE!”
• Similar signals also tells transcription to stop.
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RNA Editing• Some RNA molecules need to be edited before
they are ready for making proteins.
• Sometimes large sequences must be removed so that the RNA can make a functional protein. These intervening sequences are called introns.
• The remaining portions or expressed sequences are called exons. They are spliced back together to form the final draft of mRNA.
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The Genetic Code• There are 20 different amino acids found in
nature.
• Proteins are made by joining amino acids into long chains called polypeptides.
• The genetic code is read 3 letters at a time. Each set of 3 nucleotides is called a codon.
• Each codon specifies a specific amino acid.
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The Genetic Code• There are 64 different codons.
• Some amino acids have more than one codon.
• The START codon is AUG. It occurs at the beginning of EVERY protein.
• There are 3 STOP codons—UAA, UAG, and UGA.
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Translation• mRNA carries the coded message to the
ribosome. The message must then be decoded or translated so the ribosome can build the protein.
• During translation, the ribosome uses information from mRNA to produce proteins.
• Translation is carried out by tRNA and rRNA.
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Translation• Each tRNA molecule has an amino acid
attached to one end and 3 nucleotide bases at the other end.
• The 3 nucleotide bases attached to tRNA are called an anticodon because they are complementary to the codon for that amino acid.
• Example: codon = AAG anti = UUC(AAG codes for Lysine)
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Translation• tRNA can then give the correct amino
acid to the ribosome.
• The ribosome, which is made of rRNA, attaches the amino acids together to make the polypeptide chain (protein).
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DNA, RNA, and Proteins• DNA is like the master copy.
• RNA is like the blueprint the workers use.
• The workers are ribosomes.
• Proteins are the finished product.
• Proteins are the keys to almost EVERYTHING that living cells do!