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Questions and Answers
At which pH value is the α-carboxyl group of an amino acid likely to be deprotonated?
At which pH value is the α-carboxyl group of an amino acid likely to be deprotonated?
- pH = 1
- pH = 2.5
- pH = 4 (correct)
- pH = 3
Which amino acid is known for having a thiol group (-SH) in its side chain?
Which amino acid is known for having a thiol group (-SH) in its side chain?
- Cysteine (correct)
- Lysine
- Arginine
- Histidine
What is the average pKa value for the α-NH3+ group of amino acids?
What is the average pKa value for the α-NH3+ group of amino acids?
- 9.47 (correct)
- 6.9
- 7.5
- 8.2
Which amino acid contains an imidazole group in its side chain?
Which amino acid contains an imidazole group in its side chain?
At which pH value is the side chain guanidino group of arginine likely to be deprotonated?
At which pH value is the side chain guanidino group of arginine likely to be deprotonated?
Which amino acid's side chain is known to have a hydroxyl group bonded to an aromatic hydrocarbon group?
Which amino acid's side chain is known to have a hydroxyl group bonded to an aromatic hydrocarbon group?
What happens to the charge on the α-amino carboxyl group of an amino acid as the pH increases above its pKa?
What happens to the charge on the α-amino carboxyl group of an amino acid as the pH increases above its pKa?
Which amino acid has a cyclic structure and an amine as its secondary functional group?
Which amino acid has a cyclic structure and an amine as its secondary functional group?
What does the isoelectric pH (pI) represent for a compound in solution?
What does the isoelectric pH (pI) represent for a compound in solution?
How is the isoelectric pH (pI) calculated for amino acids with multiple ionizable groups?
How is the isoelectric pH (pI) calculated for amino acids with multiple ionizable groups?
In titration curves of amino acids, what does each point on the curve represent?
In titration curves of amino acids, what does each point on the curve represent?
For an amino acid with pKa values of 2.19, 9.67, and 4.25, how can you calculate its isoelectric point?
For an amino acid with pKa values of 2.19, 9.67, and 4.25, how can you calculate its isoelectric point?
What is the significance of the isoelectric point for a compound like glutamic acid?
What is the significance of the isoelectric point for a compound like glutamic acid?
What does the pI calculation involve for amino acids with complex structures?
What does the pI calculation involve for amino acids with complex structures?
How does the pI for glycine relate to its pKa values for carboxyl and amino groups?
How does the pI for glycine relate to its pKa values for carboxyl and amino groups?
In titration, what does plotting a titration curve reveal about functional groups in amino acids?
In titration, what does plotting a titration curve reveal about functional groups in amino acids?
Which statement about the amino acids is FALSE?
Which statement about the amino acids is FALSE?
At a neutral pH, how do amino acids without charged side chains exist?
At a neutral pH, how do amino acids without charged side chains exist?
What is a common feature of hydroxylysine and hydroxyproline?
What is a common feature of hydroxylysine and hydroxyproline?
Which amino acid residue is primarily found in few connective tissues like collagen?
Which amino acid residue is primarily found in few connective tissues like collagen?
What is the charge on the carboxyl group and amino group in free amino acids at neutral pH?
What is the charge on the carboxyl group and amino group in free amino acids at neutral pH?
Which amino acid has a secondary a-amino group?
Which amino acid has a secondary a-amino group?
What is unique about thyroxine in terms of its location?
What is unique about thyroxine in terms of its location?
What is the charge on glutamic acid at a pH of 1?
What is the charge on glutamic acid at a pH of 1?
For how many of the 20 amino acids is the α-amino group primary?
For how many of the 20 amino acids is the α-amino group primary?
At what pH would glutamic acid carry a net charge of zero?
At what pH would glutamic acid carry a net charge of zero?
What is the net charge on glutamic acid at a pH of 10?
What is the net charge on glutamic acid at a pH of 10?
Which pKa value is responsible for the change in charge from -2 to -1 in glutamic acid as the pH increases?
Which pKa value is responsible for the change in charge from -2 to -1 in glutamic acid as the pH increases?
At which pH do the COOH and NH3 groups in glutamic acid have equal concentrations of protonated and deprotonated forms?
At which pH do the COOH and NH3 groups in glutamic acid have equal concentrations of protonated and deprotonated forms?
What effect would decreasing the pH below 2.19 have on the charge of glutamic acid?
What effect would decreasing the pH below 2.19 have on the charge of glutamic acid?
What would be the net charge on glutamic acid at a pH of 3?
What would be the net charge on glutamic acid at a pH of 3?
If the pH is above 9.67, what would be the predominant form of glutamic acid?
If the pH is above 9.67, what would be the predominant form of glutamic acid?
Which carbon in an α-amino acid is adjacent to the carboxyl group and bound to the amino group and R-group?
Which carbon in an α-amino acid is adjacent to the carboxyl group and bound to the amino group and R-group?
What term describes the property of an amino acid having two steroisomers based on the location of the amino group on the α-carbon?
What term describes the property of an amino acid having two steroisomers based on the location of the amino group on the α-carbon?
In biological systems, which steroisomer of amino acids is predominantly produced?
In biological systems, which steroisomer of amino acids is predominantly produced?
How many 'standard' encoded amino acids are there that must be known?
How many 'standard' encoded amino acids are there that must be known?
How many amino acids are there that are known to undergo post-translation modification?
How many amino acids are there that are known to undergo post-translation modification?
Which type of carbon in an α-amino acid determines whether it is chiral or achiral?
Which type of carbon in an α-amino acid determines whether it is chiral or achiral?
Which category of amino acids includes 2 non-canonical types with special translation mechanisms?
Which category of amino acids includes 2 non-canonical types with special translation mechanisms?
'pI' in ionization of amino acids refers to what point in the titration curve?
'pI' in ionization of amino acids refers to what point in the titration curve?
What is the charge on glutamic acid at a pH of 2?
What is the charge on glutamic acid at a pH of 2?
In the pH region between 2.19 and 4.25, how many ionizable groups in glutamic acid are deprotonated?
In the pH region between 2.19 and 4.25, how many ionizable groups in glutamic acid are deprotonated?
At what pH value is the α-NH3+ group of glutamic acid expected to be deprotonated?
At what pH value is the α-NH3+ group of glutamic acid expected to be deprotonated?
Between pH 4.25 and 9.67, which ionizable group in glutamic acid will remain protonated?
Between pH 4.25 and 9.67, which ionizable group in glutamic acid will remain protonated?
What is the net charge on glutamic acid at its isoelectric point?
What is the net charge on glutamic acid at its isoelectric point?
If the pH is 3, what contributes to the negative charge on glutamic acid?
If the pH is 3, what contributes to the negative charge on glutamic acid?
At a pH of 5, which functional group of glutamic acid will likely be predominantly protonated?
At a pH of 5, which functional group of glutamic acid will likely be predominantly protonated?
What is the effect of increasing the pH above 9.67 on the overall charge of glutamic acid?
What is the effect of increasing the pH above 9.67 on the overall charge of glutamic acid?
Which amino acid is known for producing two steroisomers, L and D, based on where the amino group is present on the α-carbon?
Which amino acid is known for producing two steroisomers, L and D, based on where the amino group is present on the α-carbon?
What type of amino acids undergo post-translation modification among the known amino acids?
What type of amino acids undergo post-translation modification among the known amino acids?
How many amino acids are typically involved in the standard encoded amino acids that must be known?
How many amino acids are typically involved in the standard encoded amino acids that must be known?
At what pH value would an amino acid primarily exist in its zwitterionic form?
At what pH value would an amino acid primarily exist in its zwitterionic form?
Which type of carbon in an α-amino acid plays a crucial role in determining chirality?
Which type of carbon in an α-amino acid plays a crucial role in determining chirality?
In titration curves of amino acids, what does a steep change in pH indicate?
In titration curves of amino acids, what does a steep change in pH indicate?
What is the significance of the pKa values 2.19, 9.67, and 4.25 for an amino acid?
What is the significance of the pKa values 2.19, 9.67, and 4.25 for an amino acid?
"What does each point on a titration curve of an amino acid represent?"
"What does each point on a titration curve of an amino acid represent?"
What is the primary functional group that changes its charge state in amino acids during titration?
What is the primary functional group that changes its charge state in amino acids during titration?
In the context of amino acid titration, what is the significance of the pKa value?
In the context of amino acid titration, what is the significance of the pKa value?
What is the relationship between the isoelectric pH (pI) and the charge of an amino acid in solution?
What is the relationship between the isoelectric pH (pI) and the charge of an amino acid in solution?
How does changing the pH impact the charge on the α-amino group of amino acids?
How does changing the pH impact the charge on the α-amino group of amino acids?
At what pH level would an amino acid primarily exist in its zwitterionic form?
At what pH level would an amino acid primarily exist in its zwitterionic form?
Which factor determines the net charge on glutamic acid at a given pH?
Which factor determines the net charge on glutamic acid at a given pH?
What does the pI (isoelectric point) of a compound represent?
What does the pI (isoelectric point) of a compound represent?
How does the net charge on glutamic acid change when the pH is above its $pKa$ of 4.25?
How does the net charge on glutamic acid change when the pH is above its $pKa$ of 4.25?
How can the isoelectric point (pI) for amino acids with multiple ionizable groups be calculated?
How can the isoelectric point (pI) for amino acids with multiple ionizable groups be calculated?
What happens to the concentration of protonated and deprotonated forms of COOH and NH3 in glutamic acid at its $pI$?
What happens to the concentration of protonated and deprotonated forms of COOH and NH3 in glutamic acid at its $pI$?
Which pH region would result in a net charge of zero for glutamic acid?
Which pH region would result in a net charge of zero for glutamic acid?
What significance does the pI calculation hold for more complex amino acids like glutamic acid?
What significance does the pI calculation hold for more complex amino acids like glutamic acid?
If an amino acid is found in a solution with a pH above its pKa (α-NH3+), what can be said about its charge?
If an amino acid is found in a solution with a pH above its pKa (α-NH3+), what can be said about its charge?
What affects the variation in net charge of an amino acid within different pH ranges?
What affects the variation in net charge of an amino acid within different pH ranges?
How does the pH-region method contribute to calculating the pI of amino acids?
How does the pH-region method contribute to calculating the pI of amino acids?
At which pH value do amino acids with complex structures like glutamic acid generally carry no net charge?
At which pH value do amino acids with complex structures like glutamic acid generally carry no net charge?
What defines the isoelectric point (pI) of an amino acid in solution?
What defines the isoelectric point (pI) of an amino acid in solution?
At what pH does the carboxyl group of an amino acid like aspartic acid carry a negative charge?
At what pH does the carboxyl group of an amino acid like aspartic acid carry a negative charge?
Which group in amino acids has a considerably stronger base in its protonated form relative to its neutral form?
Which group in amino acids has a considerably stronger base in its protonated form relative to its neutral form?
What is the significance of pH relative to the pKa value in determining the charge state of an amino acid's side chain?
What is the significance of pH relative to the pKa value in determining the charge state of an amino acid's side chain?
At what pH does the α-amino group in amino acids like lysine carry a positive charge?
At what pH does the α-amino group in amino acids like lysine carry a positive charge?
What is the condition for an amino acid to be neutral in charge in a titration curve?
What is the condition for an amino acid to be neutral in charge in a titration curve?
Which amino acid residue would be predominantly protonated at a pH below its pKa value of 3.0?
Which amino acid residue would be predominantly protonated at a pH below its pKa value of 3.0?
If the pH is raised above 10, what charge does the side chain of glutamic acid carry?
If the pH is raised above 10, what charge does the side chain of glutamic acid carry?
Study Notes
Amino Acid Properties
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The α-carboxyl group of an amino acid is likely to be deprotonated at a pH value above its pKa.
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Cysteine is the amino acid known for having a thiol group (-SH) in its side chain.
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The average pKa value for the α-NH3+ group of amino acids is around 9-10.
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Histidine is the amino acid that contains an imidazole group in its side chain.
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The side chain guanidino group of arginine is likely to be deprotonated at a pH value above 12.
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Tyrosine is the amino acid whose side chain is known to have a hydroxyl group bonded to an aromatic hydrocarbon group.
Isoelectric Point (pI)
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The isoelectric pH (pI) represents the pH at which a compound in solution has a net charge of zero.
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For amino acids with multiple ionizable groups, the pI is calculated by taking the average of the pKa values of the ionizable groups.
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In titration curves of amino acids, each point on the curve represents the degree of protonation or deprotonation of the ionizable groups.
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At the pI, the concentrations of protonated and deprotonated forms of the ionizable groups are equal.
Titration Curves
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Titration curves reveal the pH range over which each ionizable group of an amino acid is protonated or deprotonated.
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Each steep change in pH on the curve indicates a change in the charge state of an ionizable group.
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The pKa value is significant because it indicates the pH range at which an ionizable group is 50% protonated and 50% deprotonated.
Amino Acid Structure
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The α-carbon in an α-amino acid is adjacent to the carboxyl group and bound to the amino group and R-group.
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The term "chirality" describes the property of an amino acid having two stereoisomers based on the location of the amino group on the α-carbon.
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In biological systems, the L-stereoisomer of amino acids is predominantly produced.
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There are 20 "standard" encoded amino acids that must be known.
Amino Acid Ionization
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The net charge on an amino acid changes as the pH increases or decreases, due to changes in the charge state of the ionizable groups.
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The pH-region method can be used to calculate the pI of amino acids with multiple ionizable groups.
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At a pH below its pKa, the α-amino group of an amino acid is protonated and carries a positive charge.
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At a pH above its pKa, the α-carboxyl group of an amino acid is deprotonated and carries a negative charge.
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Description
Test your knowledge on the classification of amino acids based on R-group characteristics such as aliphatic, aromatic, cyclic, acidic, basic, sulfur, amide bonds, polar or non-polar. Explore how amino acids are categorized according to the site of attachment of the functional group and greek notation like α-, β-, γ-, δ-.
