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Protein Synthesis

This review covers the process of protein synthesis, including the structure of amino acids, the genetic code, and translation. It also explains how proteins are made from amino acids and the role of ribosomes in this process.

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Protein Synthesis

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  1. Protein Synthesis Chapter 12 Section 3 Pg. 302-306

  2. Proteins Review • Elements: C, H, O, N • Monomer = Amino Acids (20 kinds) • Foods- Fish, poultry, soy, beans

  3. Proteins Review • Amino acids are connected by peptide bonds during dehydration synthesis reactions. • The sequence of amino acids determines the folding and shape of proteins. • The shape of the proteins determines the function. • Protein function is also affected by temperature and pH fluctuations.

  4. Amino Acid Structure Review A central carbon with four things attached: • A single hydrogen atom • A carboxyl group (–COOH) • An amino group (–NH2) • An R group - functional group which is different for each amino acid • Amino acids are connected during dehydration synthesis reactions

  5. Going from DNA to Proteins • What have we done so far? • The DNA message is converted into RNA in a process called transcription. We get: • mRNA with the DNA code • tRNA waiting with the amino acid • rRNA making ribosomes for translation • This happens in the nucleus. • Our proteins are made from Amino Acids so we need a bridge to go from the RNA we just made to amino acids…

  6. The Genetic Code • The language of mRNA is called the Genetic Code (A, G, U, C) and contains only 4 letters. • It is based on codons, which are 3 bases together on an mRNA chain (like 3 letter words). • Each codon codes for a specific amino acid. • There are 64 codons and 20 amino acids so several codons will code for the same amino acid. NOTE: The Genetic Code is Universal: Most organisms follow the same code to produce proteins, demonstrating that we are all evolutionarily related.

  7. Special Codons: Start/Stop Condons • Start Codon: AUG • Signals the beginning of protein synthesis/translation • Protein synthesis can only begin at this codon. • Also codes for the Amino Acid: Methionine • Stop Codons: UAA, UAG, UGA • Signals protein synthesis to stop. • Similar to the period at the end of a sentence.

  8. Genetic Code Square

  9. Genetic Code Circle

  10. How do we get from RNA to Proteins? Translation!! Changing the DNA code into actual proteins the cell can use. It happens in the ribosome.

  11. tRNA and Anticodons • Amino acids are free floating in the cytosol and are carried to the ribosome by tRNA molecules • Top part of loop allows for 1 AA to bind • Bottom part of loop is the anticodon (sequence of 3 nucleotides) that pairs with its complementary mRNA • Ex: mRNA codon: GCC tRNA anticodon: CGG Note: the pairing of a anticodon with a codon ensures that the Amino Acids are joined in the correct order

  12. Setting the Stage for Translation… • mRNA has been made and is moving to the ribosome • tRNA’s are transporting the amino acids to the ribosome. • Translation is ready to begin. http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html

  13. Steps of Translation • Step 1: Ribosomes attach to the start codon (AUG) of the mRNA. • Step 2: A tRNA with the anticodon of UAC and a methionine binds to the mRNA inside the ribosome. • Step 3: In the 2nd binding site, the next codon is read and a tRNA is attached. A peptide bond forms between the two amino acids.

  14. Steps of Translation (continued) • Step 4:The 1st tRNA is released and the ribosome moves to the next codon. • Step 5: The process continues until a stop codon is reached. Translation stops and the ribosome releases the mRNA and the created protein.

  15. Protein Synthesis Analogy

  16. Animations http://biology.kenyon.edu/slonc/bio3/ribo/ribo3.html http://www.youtube.com/watch?v=NJxobgkPEAo http://video.google.com/videoplay?docid=-4167644462303807708&q=the+human+genome+project+video&hl=en

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