80 Questions
At which pH value is the α-carboxyl group of an amino acid likely to be deprotonated?
pH = 4
Which amino acid is known for having a thiol group (-SH) in its side chain?
Cysteine
What is the average pKa value for the α-NH3+ group of amino acids?
9.47
Which amino acid contains an imidazole group in its side chain?
Histidine
At which pH value is the side chain guanidino group of arginine likely to be deprotonated?
pH = 10
Which amino acid's side chain is known to have a hydroxyl group bonded to an aromatic hydrocarbon group?
Tyrosine
What happens to the charge on the α-amino carboxyl group of an amino acid as the pH increases above its pKa?
It becomes negatively charged
Which amino acid has a cyclic structure and an amine as its secondary functional group?
Proline
What does the isoelectric pH (pI) represent for a compound in solution?
The pH at which the compound has no net charge
How is the isoelectric pH (pI) calculated for amino acids with multiple ionizable groups?
By using the two pKa values that bound the neutral region
In titration curves of amino acids, what does each point on the curve represent?
Charge of the amino acid at a specific pH
For an amino acid with pKa values of 2.19, 9.67, and 4.25, how can you calculate its isoelectric point?
Using the two pKa values that bound the neutral region
What is the significance of the isoelectric point for a compound like glutamic acid?
It represents the pH where glutamic acid has a net charge of zero
What does the pI calculation involve for amino acids with complex structures?
Using specific pKa values to identify neutrality
How does the pI for glycine relate to its pKa values for carboxyl and amino groups?
It falls exactly between the two pKa values
In titration, what does plotting a titration curve reveal about functional groups in amino acids?
Their charge at various pH levels
Which statement about the amino acids is FALSE?
Isoleucine and threonine have only one stereocenter.
At a neutral pH, how do amino acids without charged side chains exist?
As zwitterions with no net charge.
What is a common feature of hydroxylysine and hydroxyproline?
They are post-translation modifications of common amino acids.
Which amino acid residue is primarily found in few connective tissues like collagen?
Hydroxylysine
What is the charge on the carboxyl group and amino group in free amino acids at neutral pH?
- on carboxyl group, - on amino group
Which amino acid has a secondary a-amino group?
Proline
What is unique about thyroxine in terms of its location?
It's found only in the thyroid gland.
What is the charge on glutamic acid at a pH of 1?
-1
For how many of the 20 amino acids is the α-amino group primary?
19
At what pH would glutamic acid carry a net charge of zero?
5.73
What is the net charge on glutamic acid at a pH of 10?
-3
Which pKa value is responsible for the change in charge from -2 to -1 in glutamic acid as the pH increases?
pKa (R) = 4.25
At which pH do the COOH and NH3 groups in glutamic acid have equal concentrations of protonated and deprotonated forms?
9.67
What effect would decreasing the pH below 2.19 have on the charge of glutamic acid?
Net charge will increase
What would be the net charge on glutamic acid at a pH of 3?
-2
If the pH is above 9.67, what would be the predominant form of glutamic acid?
-COO- and -NH2
Which carbon in an α-amino acid is adjacent to the carboxyl group and bound to the amino group and R-group?
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?
Chiral
In biological systems, which steroisomer of amino acids is predominantly produced?
L-isomer
How many 'standard' encoded amino acids are there that must be known?
20
How many amino acids are there that are known to undergo post-translation modification?
450
Which type of carbon in an α-amino acid determines whether it is chiral or achiral?
α-carbon
Which category of amino acids includes 2 non-canonical types with special translation mechanisms?
'Non-standard' encoded amino acids
'pI' in ionization of amino acids refers to what point in the titration curve?
'Point of Inflection'
What is the charge on glutamic acid at a pH of 2?
-3
In the pH region between 2.19 and 4.25, how many ionizable groups in glutamic acid are deprotonated?
1
At what pH value is the α-NH3+ group of glutamic acid expected to be deprotonated?
9.67
Between pH 4.25 and 9.67, which ionizable group in glutamic acid will remain protonated?
α-COOH
What is the net charge on glutamic acid at its isoelectric point?
-1
If the pH is 3, what contributes to the negative charge on glutamic acid?
R group
At a pH of 5, which functional group of glutamic acid will likely be predominantly protonated?
+NH3 group
What is the effect of increasing the pH above 9.67 on the overall charge of glutamic acid?
-1 charge decrease
Which amino acid is known for producing two steroisomers, L and D, based on where the amino group is present on the α-carbon?
Phenylalanine
What type of amino acids undergo post-translation modification among the known amino acids?
Non-canonical amino acids
How many amino acids are typically involved in the standard encoded amino acids that must be known?
20
At what pH value would an amino acid primarily exist in its zwitterionic form?
At the isoelectric point (pI)
Which type of carbon in an α-amino acid plays a crucial role in determining chirality?
α-carbon
In titration curves of amino acids, what does a steep change in pH indicate?
Buffering region
What is the significance of the pKa values 2.19, 9.67, and 4.25 for an amino acid?
"These values help calculate its isoelectric point"
"What does each point on a titration curve of an amino acid represent?"
"Protonation state of the functional groups"
What is the primary functional group that changes its charge state in amino acids during titration?
Carboxyl group
In the context of amino acid titration, what is the significance of the pKa value?
Reflects the equilibrium between protonated and deprotonated forms
What is the relationship between the isoelectric pH (pI) and the charge of an amino acid in solution?
Amino acids are neutral at their pI
How does changing the pH impact the charge on the α-amino group of amino acids?
The positive charge increases as pH decreases
At what pH level would an amino acid primarily exist in its zwitterionic form?
$pH = pKa$
Which factor determines the net charge on glutamic acid at a given pH?
$pH$ relative to its $pKa$ values
What does the pI (isoelectric point) of a compound represent?
The pH at which the compound has no net charge
How does the net charge on glutamic acid change when the pH is above its $pKa$ of 4.25?
-1 to -2
How can the isoelectric point (pI) for amino acids with multiple ionizable groups be calculated?
By finding the pH region where the amino acid is neutral
What happens to the concentration of protonated and deprotonated forms of COOH and NH3 in glutamic acid at its $pI$?
$[COOH] = [NH3]$ but their sum equals 1
Which pH region would result in a net charge of zero for glutamic acid?
pH = 4.25
What significance does the pI calculation hold for more complex amino acids like glutamic acid?
Helps understand the pH range of neutrality
If an amino acid is found in a solution with a pH above its pKa (α-NH3+), what can be said about its charge?
Net negative charge
What affects the variation in net charge of an amino acid within different pH ranges?
Ionization state
How does the pH-region method contribute to calculating the pI of amino acids?
It simplifies identifying regions of neutrality
At which pH value do amino acids with complex structures like glutamic acid generally carry no net charge?
$pH = (2.19 + 9.67) / 2$
What defines the isoelectric point (pI) of an amino acid in solution?
The pH at which the amino acid has no net charge
At what pH does the carboxyl group of an amino acid like aspartic acid carry a negative charge?
pH < 2.19
Which group in amino acids has a considerably stronger base in its protonated form relative to its neutral form?
Arginine's guanidino group
What is the significance of pH relative to the pKa value in determining the charge state of an amino acid's side chain?
pH > pKa = deprotonated
At what pH does the α-amino group in amino acids like lysine carry a positive charge?
pH > 9.47
What is the condition for an amino acid to be neutral in charge in a titration curve?
pH = isoelectric point (pI)
Which amino acid residue would be predominantly protonated at a pH below its pKa value of 3.0?
Histidine
If the pH is raised above 10, what charge does the side chain of glutamic acid carry?
-2
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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