BIO130 Section One Guide (3)

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26 Apr 2011

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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 chaperones often assist in protein
oAlso 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
oLarge proteins consist of protein domains which fold mostly independent of
each other
The α Helix and the Sheet are Common Folding Patterns
-α helix was found in the protein α-keratin, abundant in skin, hair, nails, horns
- sheet was found in the protein fibroin, the major constituent of silk
oboth 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
2. from a polypeptide chain that folds back and forth upon itself (anti-
parallel chains)
-αhelix is made through twisting a single polypeptide chain around to form a rigid
oA hydrogen bond is formed every 4th peptide bond (N-H and C=O)
oComplete turn every 3.6 amino acids
oFound in cell membranes (transport proteins, receptors)
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