BIO130 Section One Guide (3)

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Kenneth Yip

Chapter 3 Proteins (pg. 125-152) - Proteins such as kinesin propel organelles through the cytoplasm, topoisomerase untangles knotted DNA molecules The Shape and Structure of Proteins The Shape of a Protein Is Specified by Its Amino Acid Sequence - Proteins are long polymers of amino acids linked by peptide bonds, and they are always written with the N-terminus toward the left - * special case: two cysteine side chains can form disulfide bonds Proteins Fold into a Conformation of Lowest Energy - The final folded structure, or conformation, of any polypeptide chain is generally the one that minimizes its free energy - In living cells, special proteins called molecular chaperonesoften assist in protein folding o Also prevent exposed hydrophobic regions in newly synthesized protein chains from associating with each other to form protein aggregates - Proteins are generally between 50-2000 amino acids long o Large proteins consist of protein domains which fold mostly independent of each other The Helix and the Sheet are Common Folding Patterns - helix was found in the protein -keratin, abundant in skin, hair, nails, horns - sheet was found in the protein fibroin, the major constituent of silk o both patterns result from hydrogen bonding between N-H and C=O groups in the polypeptide backbone - sheets (forming the core of many proteins) can form either (via hydrogen bonds): 1. from neighbouring polypeptide chains running in the same orientation (parallel) 2. from a polypeptide chain that folds back and forth upon itself (anti- parallel chains) - helix is made through twisting a single polypeptide chain around to form a rigid cylinder o A hydrogen bond is formed every 4 peptide bond (N-H and C=O) o Complete turn every 3.6 amino acids o Found in cell membranes (transport proteins, receptors)
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