Topic 4: Proteins: Structure and Folding

Protein folding, structural levels, and mechanisms.

Levels of Protein Structure

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Which one of the following levels of protein structure correspond to the description 'homo- and hetero-oligomers'.

• A. primary 
• B. quaternary 
• C. secondary 
• D. tertiary 

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Hydrogen Bonding in Alpha-Helix Structures

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The α-helix is a right-handed coil in which each backbone N–H group forms a hydrogen bond with the C=O group of an amino acid located a few residues away. The regular pattern of hydrogen bonding stabilizes the helix, preventing it from unraveling.
In a long α-helix, amino acid number 7 would form a hydrogen bond with which two other amino acids?
Select the correct pair of amino acids below.

• A. amino acids 6 and 8 (a residue shift of 1 position) 
• B. amino acids 5 and 9 (a residue shift of 2 positions) 
• C. amino acids 4 and 10 (a residue shift of 3 positions) 
• D. amino acids 3 and 11 (a residue shift of 4 positions) 
• E. amino acids 2 and 12 (a residue shift of 5 positions) 

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Ionic Bond Formation in Amino Acid Side Chains

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Based on the chemical properties of amino acid side chains, which pair of amino acids listed below can form an ionic bond between their side chains?

• A. Cysteine and Glutamine 
• B. Asparagine and Isoleucine 
• C. Lysine and Glutamic Acid 
• D. Glutamine and Aspartate 
• E. Proline and Arginine 

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