Amino Acid Classification based on R-group and Characteristics
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Questions and Answers

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?

  • Cysteine (correct)
  • Lysine
  • Arginine
  • Histidine

    • 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?

    <p>Histidine</p> Signup and view all the answers

    At which pH value is the side chain guanidino group of arginine likely to be deprotonated?

    <p>pH = 10</p> Signup and view all the answers

    Which amino acid's side chain is known to have a hydroxyl group bonded to an aromatic hydrocarbon group?

    <p>Tyrosine</p> Signup and view all the answers

    What happens to the charge on the α-amino carboxyl group of an amino acid as the pH increases above its pKa?

    <p>It becomes negatively charged</p> Signup and view all the answers

    Which amino acid has a cyclic structure and an amine as its secondary functional group?

    <p>Proline</p> Signup and view all the answers

    What does the isoelectric pH (pI) represent for a compound in solution?

    <p>The pH at which the compound has no net charge</p> Signup and view all the answers

    How is the isoelectric pH (pI) calculated for amino acids with multiple ionizable groups?

    <p>By using the two pKa values that bound the neutral region</p> Signup and view all the answers

    In titration curves of amino acids, what does each point on the curve represent?

    <p>Charge of the amino acid at a specific pH</p> Signup and view all the answers

    For an amino acid with pKa values of 2.19, 9.67, and 4.25, how can you calculate its isoelectric point?

    <p>Using the two pKa values that bound the neutral region</p> Signup and view all the answers

    What is the significance of the isoelectric point for a compound like glutamic acid?

    <p>It represents the pH where glutamic acid has a net charge of zero</p> Signup and view all the answers

    What does the pI calculation involve for amino acids with complex structures?

    <p>Using specific pKa values to identify neutrality</p> Signup and view all the answers

    How does the pI for glycine relate to its pKa values for carboxyl and amino groups?

    <p>It falls exactly between the two pKa values</p> Signup and view all the answers

    In titration, what does plotting a titration curve reveal about functional groups in amino acids?

    <p>Their charge at various pH levels</p> Signup and view all the answers

    Which statement about the amino acids is FALSE?

    <p>Isoleucine and threonine have only one stereocenter.</p> Signup and view all the answers

    At a neutral pH, how do amino acids without charged side chains exist?

    <p>As zwitterions with no net charge.</p> Signup and view all the answers

    What is a common feature of hydroxylysine and hydroxyproline?

    <p>They are post-translation modifications of common amino acids.</p> Signup and view all the answers

    Which amino acid residue is primarily found in few connective tissues like collagen?

    <p>Hydroxylysine</p> Signup and view all the answers

    What is the charge on the carboxyl group and amino group in free amino acids at neutral pH?

    <ul> <li>on carboxyl group, - on amino group</li> </ul> Signup and view all the answers

    Which amino acid has a secondary a-amino group?

    <p>Proline</p> Signup and view all the answers

    What is unique about thyroxine in terms of its location?

    <p>It's found only in the thyroid gland.</p> Signup and view all the answers

    What is the charge on glutamic acid at a pH of 1?

    <p>-1</p> Signup and view all the answers

    For how many of the 20 amino acids is the α-amino group primary?

    <p>19</p> Signup and view all the answers

    At what pH would glutamic acid carry a net charge of zero?

    <p>5.73</p> Signup and view all the answers

    What is the net charge on glutamic acid at a pH of 10?

    <p>-3</p> Signup and view all the answers

    Which pKa value is responsible for the change in charge from -2 to -1 in glutamic acid as the pH increases?

    <p>pKa (R) = 4.25</p> Signup and view all the answers

    At which pH do the COOH and NH3 groups in glutamic acid have equal concentrations of protonated and deprotonated forms?

    <p>9.67</p> Signup and view all the answers

    What effect would decreasing the pH below 2.19 have on the charge of glutamic acid?

    <p>Net charge will increase</p> Signup and view all the answers

    What would be the net charge on glutamic acid at a pH of 3?

    <p>-2</p> Signup and view all the answers

    If the pH is above 9.67, what would be the predominant form of glutamic acid?

    <p>-COO- and -NH2</p> Signup and view all the answers

    Which carbon in an α-amino acid is adjacent to the carboxyl group and bound to the amino group and R-group?

    <p>α-carbon</p> Signup and view all the answers

    What term describes the property of an amino acid having two steroisomers based on the location of the amino group on the α-carbon?

    <p>Chiral</p> Signup and view all the answers

    In biological systems, which steroisomer of amino acids is predominantly produced?

    <p>L-isomer</p> Signup and view all the answers

    How many 'standard' encoded amino acids are there that must be known?

    <p>20</p> Signup and view all the answers

    How many amino acids are there that are known to undergo post-translation modification?

    <p>450</p> Signup and view all the answers

    Which type of carbon in an α-amino acid determines whether it is chiral or achiral?

    <p>α-carbon</p> Signup and view all the answers

    Which category of amino acids includes 2 non-canonical types with special translation mechanisms?

    <p>'Non-standard' encoded amino acids</p> Signup and view all the answers

    'pI' in ionization of amino acids refers to what point in the titration curve?

    <p>'Point of Inflection'</p> Signup and view all the answers

    What is the charge on glutamic acid at a pH of 2?

    <p>-3</p> Signup and view all the answers

    In the pH region between 2.19 and 4.25, how many ionizable groups in glutamic acid are deprotonated?

    <p>1</p> Signup and view all the answers

    At what pH value is the α-NH3+ group of glutamic acid expected to be deprotonated?

    <p>9.67</p> Signup and view all the answers

    Between pH 4.25 and 9.67, which ionizable group in glutamic acid will remain protonated?

    <p>α-COOH</p> Signup and view all the answers

    What is the net charge on glutamic acid at its isoelectric point?

    <p>-1</p> Signup and view all the answers

    If the pH is 3, what contributes to the negative charge on glutamic acid?

    <p>R group</p> Signup and view all the answers

    At a pH of 5, which functional group of glutamic acid will likely be predominantly protonated?

    <p>+NH3 group</p> Signup and view all the answers

    What is the effect of increasing the pH above 9.67 on the overall charge of glutamic acid?

    <p>-1 charge decrease</p> Signup and view all the answers

    Which amino acid is known for producing two steroisomers, L and D, based on where the amino group is present on the α-carbon?

    <p>Phenylalanine</p> Signup and view all the answers

    What type of amino acids undergo post-translation modification among the known amino acids?

    <p>Non-canonical amino acids</p> Signup and view all the answers

    How many amino acids are typically involved in the standard encoded amino acids that must be known?

    <p>20</p> Signup and view all the answers

    At what pH value would an amino acid primarily exist in its zwitterionic form?

    <p>At the isoelectric point (pI)</p> Signup and view all the answers

    Which type of carbon in an α-amino acid plays a crucial role in determining chirality?

    <p>α-carbon</p> Signup and view all the answers

    In titration curves of amino acids, what does a steep change in pH indicate?

    <p>Buffering region</p> Signup and view all the answers

    What is the significance of the pKa values 2.19, 9.67, and 4.25 for an amino acid?

    <p>&quot;These values help calculate its isoelectric point&quot;</p> Signup and view all the answers

    "What does each point on a titration curve of an amino acid represent?"

    <p>&quot;Protonation state of the functional groups&quot;</p> Signup and view all the answers

    What is the primary functional group that changes its charge state in amino acids during titration?

    <p>Carboxyl group</p> Signup and view all the answers

    In the context of amino acid titration, what is the significance of the pKa value?

    <p>Reflects the equilibrium between protonated and deprotonated forms</p> Signup and view all the answers

    What is the relationship between the isoelectric pH (pI) and the charge of an amino acid in solution?

    <p>Amino acids are neutral at their pI</p> Signup and view all the answers

    How does changing the pH impact the charge on the α-amino group of amino acids?

    <p>The positive charge increases as pH decreases</p> Signup and view all the answers

    At what pH level would an amino acid primarily exist in its zwitterionic form?

    <p>$pH = pKa$</p> Signup and view all the answers

    Which factor determines the net charge on glutamic acid at a given pH?

    <p>$pH$ relative to its $pKa$ values</p> Signup and view all the answers

    What does the pI (isoelectric point) of a compound represent?

    <p>The pH at which the compound has no net charge</p> Signup and view all the answers

    How does the net charge on glutamic acid change when the pH is above its $pKa$ of 4.25?

    <p>-1 to -2</p> Signup and view all the answers

    How can the isoelectric point (pI) for amino acids with multiple ionizable groups be calculated?

    <p>By finding the pH region where the amino acid is neutral</p> Signup and view all the answers

    What happens to the concentration of protonated and deprotonated forms of COOH and NH3 in glutamic acid at its $pI$?

    <p>$[COOH] = [NH3]$ but their sum equals 1</p> Signup and view all the answers

    Which pH region would result in a net charge of zero for glutamic acid?

    <p>pH = 4.25</p> Signup and view all the answers

    What significance does the pI calculation hold for more complex amino acids like glutamic acid?

    <p>Helps understand the pH range of neutrality</p> Signup and view all the answers

    If an amino acid is found in a solution with a pH above its pKa (α-NH3+), what can be said about its charge?

    <p>Net negative charge</p> Signup and view all the answers

    What affects the variation in net charge of an amino acid within different pH ranges?

    <p>Ionization state</p> Signup and view all the answers

    How does the pH-region method contribute to calculating the pI of amino acids?

    <p>It simplifies identifying regions of neutrality</p> Signup and view all the answers

    At which pH value do amino acids with complex structures like glutamic acid generally carry no net charge?

    <p>$pH = (2.19 + 9.67) / 2$</p> Signup and view all the answers

    What defines the isoelectric point (pI) of an amino acid in solution?

    <p>The pH at which the amino acid has no net charge</p> Signup and view all the answers

    At what pH does the carboxyl group of an amino acid like aspartic acid carry a negative charge?

    <p>pH &lt; 2.19</p> Signup and view all the answers

    Which group in amino acids has a considerably stronger base in its protonated form relative to its neutral form?

    <p>Arginine's guanidino group</p> Signup and view all the answers

    What is the significance of pH relative to the pKa value in determining the charge state of an amino acid's side chain?

    <p>pH &gt; pKa = deprotonated</p> Signup and view all the answers

    At what pH does the α-amino group in amino acids like lysine carry a positive charge?

    <p>pH &gt; 9.47</p> Signup and view all the answers

    What is the condition for an amino acid to be neutral in charge in a titration curve?

    <p>pH = isoelectric point (pI)</p> Signup and view all the answers

    Which amino acid residue would be predominantly protonated at a pH below its pKa value of 3.0?

    <p>Histidine</p> Signup and view all the answers

    If the pH is raised above 10, what charge does the side chain of glutamic acid carry?

    <p>-2</p> Signup and view all the answers

    Study Notes

    Amino Acid Properties

    • The α-carboxyl group of an amino acid is likely to be deprotonated at a pH value above its pKa.

    • Cysteine is the amino acid known for having a thiol group (-SH) in its side chain.

    • The average pKa value for the α-NH3+ group of amino acids is around 9-10.

    • Histidine is the amino acid that contains an imidazole group in its side chain.

    • The side chain guanidino group of arginine is likely to be deprotonated at a pH value above 12.

    • Tyrosine is the amino acid whose side chain is known to have a hydroxyl group bonded to an aromatic hydrocarbon group.

    Isoelectric Point (pI)

    • The isoelectric pH (pI) represents the pH at which a compound in solution has a net charge of zero.

    • For amino acids with multiple ionizable groups, the pI is calculated by taking the average of the pKa values of the ionizable groups.

    • In titration curves of amino acids, each point on the curve represents the degree of protonation or deprotonation of the ionizable groups.

    • At the pI, the concentrations of protonated and deprotonated forms of the ionizable groups are equal.

    Titration Curves

    • Titration curves reveal the pH range over which each ionizable group of an amino acid is protonated or deprotonated.

    • Each steep change in pH on the curve indicates a change in the charge state of an ionizable group.

    • 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

    • The α-carbon in an α-amino acid is adjacent to the carboxyl group and bound to the amino group and R-group.

    • 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.

    • In biological systems, the L-stereoisomer of amino acids is predominantly produced.

    • There are 20 "standard" encoded amino acids that must be known.

    Amino Acid Ionization

    • 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.

    • The pH-region method can be used to calculate the pI of amino acids with multiple ionizable groups.

    • At a pH below its pKa, the α-amino group of an amino acid is protonated and carries a positive charge.

    • 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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    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-.

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