GRE Subject Test: Chemistry : Proteins
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Example Questions
Example Question #1 :Peptide Bonds
How many water molecules are lost from the condensation of 100 amino acids into a polypeptide?
A peptide bond is formed via the condensation of one amino acid's alpha-carboxy group with the alpha-amino group of another amino acid. Thus, the joining together of two amino acids results in the loss of one water molecule. Likewise, joining three amino acids together results in the loss of two water molecules. Following this pattern, we can conclude that the number of water molecules lost is equal to the number of amino acids joined together, minus 1. Therefore, the joining together of 100 amino acids results in the loss of 99 water molecules.
Example Question #41 :Proteins
An enzyme that cleaves disulfide bridges would most disrupt a protein containing which amino acid sequence?
Val–Leu–Leu–Cys–Tyr–Thr
Tyr–Cys–Val–Val–Leu–Thr
All of the answers would be equally affected
Tyr–Cys–Cys–Thr–Val–Leu
Cys–Leu–Val–Tyr–Tyr–Thr
Tyr–Cys–Cys–Thr–Val–Leu
Disulfide bridges are made between two cysteine amino acids. An enzyme that cleaves disulfide bonds would disrupt a protein containing the most cysteine residues; therefore, Tyr–Cys–Cys–Thr–Val–Leu is the correct answer.
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