BIOCHEMISTRY EXAM QUESTIONS AND
ANSWERS
As a piece of bacon is heated in a skillet on the stove, you observe that the
appearance of the bacon changes. You may even notice that the bacon becomes
crispy if left in the skillet.
What types of bonds or interactions in proteins are susceptible to temperature changes?
A. Hydrogen Bonds
B. Disulfide Bonds
C. Hydrophobic interactions
D. Ionic Bonds
ANS: C. Just as protein structure is
stabilized primarily by the hydrophobic effect and hydrophobic interactions, disruption of
hydrophobic interactions is the simplest way to denature a protein. This is generally done by
applying heat. High temperatures cause the atoms in a protein to move so quickly that the
structure loosens and causes the hydrophobic core to open up and expose the nonpolar residues
to water. Hydrogen bonds are stronger interactions than hydrophobic interactions and will not
be easily disrupted by heat as hydrophobic interactions will. Hydrogen bonds are disrupted by
changes in pH and by increasing the concentration of salts in the protein's environment.
If lysine is required at position #150 in the peptide chain in order for a protein to
properly fold and function, what happens if amino acid #150 is mutated from lysine
to leucine?
A. The protein will not fold properly
B. The protein will fold properly change
ANS: A. Changing
lysine (positively charged amino acid, forms ionic bonds, is hydrophilic) to leucine (a non-polar
amino acid, does not form ionic bonds, is hydrophobic) eliminates one or more important
interactions and will prevent the protein from properly folding.
Glutamine at position 16 forms an important interaction with Serine in a different
location in the protein. How would the protein structure be affected if the Glutamine in
, position 16 were mutated to Leucine? Would this increase or decrease the stability of
the protein?
A. Decrease. Glutamine and Serine formed an ionic bond that stabilized the
protein structure before the mutation. Serine and leucine do not interact.
B. Decrease. Glutamine and Serine formed a hydrogen bond that stabilized
the protein structure before the mutation. Serine and Leucine do not
interact
C. Increase. Leucine and Serine form a stronger ionic bond together
D. Approximately the same. The Glutamine-Serine interaction is similar to the Leucine-Serine
interaction
ANS: B. GIutamine and serine are both polar, uncharged amino acids that can interact by
forming a hydrogen bond. Leucine is a nonpolar amino acid that participates in hydrophobic
interactions. Since both glutamine and serine are polar, neither of them would form an ionic
bond. With this mutation, a hydrogen bond would not form and protein stability would
decrease.
•
32.
When Estrogen binds to the binding pocket of the Estrogen Receptor, it is stabilized by
hydrogen bonds. Which amino acids listed could stabilize the interaction with Estrogen
in the binding pocket of the Estrogen Receptor?
, A. Amino Acid 1
B. Amino Acid 10
C. Amino Acid 13
D. Amino Acid 3
ANS: C. The correct ANS is ‘amino acid 13’ which is a polar, uncharged amino acid that can
participate in hydrogen bonds. Amino Acid 1, is hydrophobic, as evidenced by their chains
consisting of hydrocarbons.
Hydrophobic amino acids do not participate in hydrogen bonds.
• 33.
The amino acid at position 150 (not shown) helps to stabilize the protein by forming
disulfide bonds. What amino acid is likely located at position 150? Could this amino
acid form a disulfide bond with any of the amino acids in the provided sequence
above?
A. Cysteine is at position 150. No, there are no amino acids shown that can form a disulfide bond.
B. Methionine is at position 150. No, there are no amino acids shown that can form a disulfide
bond.
C. Cysteine is at position 150. Yes, amino acid 9 can form a disulfide bond.
D. Methionine is at position 150. Yes, amino acid 9 can form a disulfide bond.
ANS: A. Cysteine is at 150. Cysteine only forms a disulfide bond with itself and it is the only
amino acid with -SH and there are no Cysteines in the sequence above.
If all of the Arginine amino acids (positions 2, 5, 8, and 12) in the sequence are
mutated to Lysine, would there be a significant effect on the protein’s stability?
A. Yes, Lysine and Arginine would repel one another because they are both positively charged
ANSWERS
As a piece of bacon is heated in a skillet on the stove, you observe that the
appearance of the bacon changes. You may even notice that the bacon becomes
crispy if left in the skillet.
What types of bonds or interactions in proteins are susceptible to temperature changes?
A. Hydrogen Bonds
B. Disulfide Bonds
C. Hydrophobic interactions
D. Ionic Bonds
ANS: C. Just as protein structure is
stabilized primarily by the hydrophobic effect and hydrophobic interactions, disruption of
hydrophobic interactions is the simplest way to denature a protein. This is generally done by
applying heat. High temperatures cause the atoms in a protein to move so quickly that the
structure loosens and causes the hydrophobic core to open up and expose the nonpolar residues
to water. Hydrogen bonds are stronger interactions than hydrophobic interactions and will not
be easily disrupted by heat as hydrophobic interactions will. Hydrogen bonds are disrupted by
changes in pH and by increasing the concentration of salts in the protein's environment.
If lysine is required at position #150 in the peptide chain in order for a protein to
properly fold and function, what happens if amino acid #150 is mutated from lysine
to leucine?
A. The protein will not fold properly
B. The protein will fold properly change
ANS: A. Changing
lysine (positively charged amino acid, forms ionic bonds, is hydrophilic) to leucine (a non-polar
amino acid, does not form ionic bonds, is hydrophobic) eliminates one or more important
interactions and will prevent the protein from properly folding.
Glutamine at position 16 forms an important interaction with Serine in a different
location in the protein. How would the protein structure be affected if the Glutamine in
, position 16 were mutated to Leucine? Would this increase or decrease the stability of
the protein?
A. Decrease. Glutamine and Serine formed an ionic bond that stabilized the
protein structure before the mutation. Serine and leucine do not interact.
B. Decrease. Glutamine and Serine formed a hydrogen bond that stabilized
the protein structure before the mutation. Serine and Leucine do not
interact
C. Increase. Leucine and Serine form a stronger ionic bond together
D. Approximately the same. The Glutamine-Serine interaction is similar to the Leucine-Serine
interaction
ANS: B. GIutamine and serine are both polar, uncharged amino acids that can interact by
forming a hydrogen bond. Leucine is a nonpolar amino acid that participates in hydrophobic
interactions. Since both glutamine and serine are polar, neither of them would form an ionic
bond. With this mutation, a hydrogen bond would not form and protein stability would
decrease.
•
32.
When Estrogen binds to the binding pocket of the Estrogen Receptor, it is stabilized by
hydrogen bonds. Which amino acids listed could stabilize the interaction with Estrogen
in the binding pocket of the Estrogen Receptor?
, A. Amino Acid 1
B. Amino Acid 10
C. Amino Acid 13
D. Amino Acid 3
ANS: C. The correct ANS is ‘amino acid 13’ which is a polar, uncharged amino acid that can
participate in hydrogen bonds. Amino Acid 1, is hydrophobic, as evidenced by their chains
consisting of hydrocarbons.
Hydrophobic amino acids do not participate in hydrogen bonds.
• 33.
The amino acid at position 150 (not shown) helps to stabilize the protein by forming
disulfide bonds. What amino acid is likely located at position 150? Could this amino
acid form a disulfide bond with any of the amino acids in the provided sequence
above?
A. Cysteine is at position 150. No, there are no amino acids shown that can form a disulfide bond.
B. Methionine is at position 150. No, there are no amino acids shown that can form a disulfide
bond.
C. Cysteine is at position 150. Yes, amino acid 9 can form a disulfide bond.
D. Methionine is at position 150. Yes, amino acid 9 can form a disulfide bond.
ANS: A. Cysteine is at 150. Cysteine only forms a disulfide bond with itself and it is the only
amino acid with -SH and there are no Cysteines in the sequence above.
If all of the Arginine amino acids (positions 2, 5, 8, and 12) in the sequence are
mutated to Lysine, would there be a significant effect on the protein’s stability?
A. Yes, Lysine and Arginine would repel one another because they are both positively charged
