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Protein Synthesis

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.

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Protein Synthesis

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  1. Protein Synthesis 12-3

  2. 2 Steps of Protein Synthesis • Transcription • Translation

  3. 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

  4. 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

  5. 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.

  6. RNA Editing • Some RNA molecules need to be edited before they are ready for making proteins. • Sometimes large sequencesmust 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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)

  11. 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).

  12. 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!

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