MCAT amino acid classification and pKa review
This study set covers high-yield facts and important relationships related to amino acid classification and pKa values for the MCAT, aiding in understanding protein structure and function.
Quiz(32 questions)
1. Which classification of amino acids does not have a charge at physiological pH?
Terms in this Study Set(32)
Amino Acid Properties(16)
What are the three classifications of amino acids?
1. Nonpolar 2. Polar 3. Charged (acidic and basic)
Which amino acids are classified as nonpolar?
Examples include: - Alanine - Valine - Leucine - Isoleucine - Methionine - Phenylalanine - Tryptophan - Proline
True or False: All polar amino acids have a charge.
False. Polar amino acids can be uncharged, e.g., Serine and Threonine.
List two acidic amino acids.
1. Aspartic acid 2. Glutamic acid
What distinguishes basic amino acids?
They have side chains that can accept protons. Examples include: - Lysine - Arginine - Histidine
True or False: Nonpolar amino acids are hydrophilic.
False. Nonpolar amino acids are hydrophobic.
Fill in the blank: The amino acid _____ is often found in protein active sites due to its basic properties.
Histidine
Compare polar and nonpolar amino acids.
Polar amino acids: - Hydrophilic - Often involved in hydrogen bonding Nonpolar amino acids: - Hydrophobic - Tend to be buried in the protein core
Which amino acid contains sulfur?
Methionine is the only amino acid that contains sulfur.
What property do all amino acids share?
They all contain an amino group (-NH2), a carboxyl group (-COOH), and a unique side chain (R group).
Name a polar uncharged amino acid.
Examples include: - Serine - Threonine - Asparagine - Glutamine
What is the charge of aspartic acid at physiological pH?
At physiological pH (around 7.4), aspartic acid carries a negative charge due to its carboxyl side chain.
True or False: Glycine is an essential amino acid.
False. Glycine is a non-essential amino acid.
Which group of amino acids typically has a pKa below 7?
Acidic amino acids, like aspartic acid and glutamic acid.
What role do charged amino acids play in protein structure?
They participate in ionic interactions, stabilizing protein structure through charge interactions.
The amino acid _____ is known for its role in forming disulfide bonds.
Cysteine, due to its thiol group (-SH).
pKa Values(16)
What is pKa?
pKa is the negative logarithm of the acid dissociation constant (Ka), representing acidity.
True or False: Lower pKa means stronger acid.
True. A lower pKa indicates a stronger acid, as it dissociates more readily.
Amino acid with pKa ~ 2.1?
Aspartic acid (Asp) has a pKa around 2.1, indicating it's acidic.
Effect of pKa on charge?
If pH < pKa, the group is protonated (positive charge). If pH > pKa, it's deprotonated (neutral/negative charge).
What is the pKa of histidine?
The pKa of the side chain of histidine is approximately 6.0.
Fill in the blank: At physiological pH (7.4), __________ is mostly uncharged.
Asparagine is mostly uncharged.
Comparison: Glutamate vs. Aspartate pKa?
Glutamate has a pKa ~ 4.25; Aspartate has a pKa ~ 3.9. Both are negatively charged at physiological pH.
pKa values of basic amino acids?
Lysine ~ 10.5, Arginine ~ 12.5, and Histidine ~ 6.0.
What happens to an amino acid with pKa 9.0 at pH 7?
It is mostly protonated and positively charged.
Charge state of a carboxyl group at pH 7?
At pH 7, carboxyl groups are deprotonated and negatively charged.
True or False: All amino acids have at least one pKa value.
True. All amino acids have at least one pKa due to their amino and carboxyl groups.
Amino acid with pKa ~ 10.5?
Lysine has a side chain pKa around 10.5.
What is the charge of cysteine at pH 7?
Cysteine is mostly neutral at pH 7 due to its thiol group pKa (~8.3).
pKa implications for enzyme activity?
Enzyme active sites often depend on the protonation state of amino acids, affecting substrate binding.
Cause and effect: High pKa in a protein.
High pKa typically means a residue is less likely to lose a proton, influencing its charge.
pKa of tyrosine?
Tyrosine has a side chain pKa around 10.1.
Questions in this Study Set(32)
1. Which classification of amino acids does not have a charge at physiological pH?
2. What does pKa indicate about an acid's strength?
3. Which amino acid would primarily be found in the interior of a protein due to its hydrophobic nature?
4. Which amino acid has a side chain pKa around 3.9?
5. True or False: Histidine can carry a positive charge at physiological pH.
6. At pH 8, what is the charge state of lysine?
7. Which amino acid is most likely to be found in an enzyme's active site due to its ability to donate or accept protons?
8. Which of the following amino acids has the highest pKa value?
9. Which amino acid is the only one with a side chain that contains a sulfur atom?
10. What is the pKa of the carboxyl group in aspartic acid?
11. Which group of amino acids is characterized by having side chains that can exist in both charged and uncharged forms?
12. Which of the following statements is TRUE regarding pKa?
13. Fill in the blank: The amino acid _____ has a side chain that can form hydrogen bonds due to its hydroxyl group.
14. At physiological pH (7.4), what is the charge of glutamate?
15. Which of the following amino acids is classified as acidic?
16. Which amino acid has a side chain pKa of approximately 10.1?
17. What type of interaction do charged amino acids typically participate in within proteins?
18. What happens to an amino acid with a pKa of 9.0 at pH 10?
19. Which amino acid is known for its role in forming disulfide bonds?
20. Which amino acid would be negatively charged at pH 7?
21. True or False: All polar amino acids are hydrophilic.
22. Which amino acid has a pKa of approximately 8.3?
23. Which amino acid has a side chain that can lose a proton at physiological pH?
24. If an amino acid has a high pKa, what can be inferred about its protonation behavior?
25. Which of the following amino acids is classified as nonpolar?
26. What is the charge of histidine at pH 6?
27. Which amino acid is classified as a basic amino acid?
28. Which of the following would NOT typically affect enzyme activity based on pKa?
29. Which amino acid is NOT considered polar?
30. What is the charge of a carboxyl group at pH 7?
31. Which of the following amino acids is NOT classified as a nonpolar amino acid?
32. Which of the following amino acids has a side chain pKa around 6.0?
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