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MCDB1A2010-Dr._Feinstein-Part_2

MCDB1A2010-Dr._Feinstein-Part_2 - Proteins Most abundant...

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Proteins Most abundant class of macromolecules 50% of dry weight of cells Most versatile macromolecules in the cell in terms of number of functions performed •serve as catalysts (enzymes) •determine cell shape (structural proteins) •hormones (insulin, growth hormone, etc) •transport molecules (hemoglobin, mem. channels, etc) •defense molecules (antibodies) •mechanical work (muscle contraction)
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How can proteins do so many different things? Structure determines Function so, if proteins can serve so many different functions, they must be able to form many different structures! How do they do that? 1. There are 20 different kinds of amino acids 2. Proteins are long chains of 10 to thousands of amino acids in length What are the 20 different amino acids? all amino acids have same basic structure but each also has a unique feature called “ R
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Generic Amino Acid Structure H H O N C C H R O H
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Table 3-1 Twenty amino acids
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Table 3-1 Twenty amino acids
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Figure 3-6 Formation of peptide bonds How do we synthesize new proteins? Peptide bond formation: another condensation/dehydration rxn aa1 + aa2 + ATP--------> aa1-aa2 + ADP + P i + H 2 O
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Building macromolecules condensation/dehydration rxns require energy. Figure 6-5 ATP
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Primary level of protein structure Figure 3-7 The four levels of protein structure
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Proteins must fold up into a final, active 3D configuration
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Secondary level of protein structure Figure 3-7 The four levels of protein structure
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Secondary level of protein structure The α -helix (left) and the γ -helix (right) as depicted in the 1951 Pauling, Corey and Branson paper Linus Pauling and Robert Corey (A) and Herman Branson (B)
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The α -helix (Left) and the γ -helix (Right), as depicted in the 1951 paper by Pauling, Corey, and Branson (1) Eisenberg D PNAS 2003;100:11207-11210
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From “Molec. Biol. Of the Cell” by Alberts et al., α helix and β sheet
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Tertiary level of protein structure larger scale intra -molecular folding interactions Quarternary level of protein structure inter -molecular folding interactions; association of multiple independent polypeptide chains Figure 3-7 The four levels of protein structure
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Figure 3-11 Non-covalent interactions between proteins and other molecules….remember those weak forces???
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