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Ribosomes and Protein Synthesis

Ribosomes and Protein Synthesis. 13.2 3/18/2011. How Genes Are Expressed. DNA. TRANSCRIPTION. RNA. TRANSLATION. PROTEIN. Protein REVIEW. Proteins are polymers of amino acids

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Ribosomes and Protein Synthesis

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  1. Ribosomes and Protein Synthesis 13.2 3/18/2011

  2. How Genes Are Expressed DNA TRANSCRIPTION RNA TRANSLATION PROTEIN

  3. Protein REVIEW • Proteins are polymers of amino acids • Proteins are also called peptides or polypeptides because the amino acids that make them up are held together by peptide bonds • There are 20 different amino acids which make up all the proteins in living things • Different numbers & combinations = different proteins with individual properties

  4. The Genetic Code • mRNA transcribed from DNA contains a code for making proteins • How is the mRNA genetic code of As, Us, Cs, and Gs “read” into a specific sequence of amino acids? • How can a code with only 4 letters contain instructions for 20 different amino acids?

  5. Reading the Genetic Code of mRNA • The genetic code is read THREE letters at a time • Each “word” is three letters long and corresponds to one specific amino acid • Each of these three letter “words” is called a codon

  6. How to Read mRNA Codons • Read the Genetic Code chart from the inside out • Start & stop codons • Think of as “punctuation” • Translation begins at start codon • AUG, the codon for methionine • Translation ends at one of three stop codons • UGA, UAA, UAG

  7. Transfer RNA • Two sided: one side has anti-codon, the other is carrying an amino acid • tRNAanti codon matches mRNA codon

  8. Protein Synthesis (Translation • During translation, or protein synthesis, the cell uses information from mRNA to produce proteins • The ribosomes of the cell read the instructions (the mRNA) and assemble the parts (the amino acids) into proteins

  9. Steps of Translation • Initiation • Ribosome attaches to mRNA in the cytoplasm • Elongation • As each mRNA codon passes through the ribosome, the tRNAs bring the appropriate amino acid • One at a time, the ribosome attaches the amino acid from the tRNA to the growing chain of amino acids (this is forming the protein) • This “assembly line” continues until… • Termination • STOP codon reached, then… • mRNA and protein released from the ribosome

  10. http://www.youtube.com/watch?v=5bLEDd-PSTQ

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