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Quizzes > Science > Chemistry

Test Your Amino Acid Knowledge - Start the Quiz!

Think you can ace this amino acids quiz game? Dive in now!

Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration for amino acid quiz on a golden yellow background

Ready to take your biochemistry knowledge higher? Dive into our amino acid quiz: a free, interactive challenge designed for students, health pros, and science buffs who want to master structures, names, and functions of these essential biomolecules. In this amino acids quiz you'll identify side chains, test your recall of single-letter codes, and explore how each residue shapes protein folding. Craving more depth? Try our protein structure and function quiz . Think you can ace this amino acids quiz game? Click 'Start' now and unlock your biochemistry mastery today!

Which amino acid contains a thiol (–SH) side chain?
Serine
Methionine
Cysteine
Tyrosine
Cysteine is unique among the standard amino acids because its side chain contains a thiol group. This thiol can form disulfide bonds, which are important for stabilizing protein structure. Methionine also contains sulfur but in a thioether, not a free thiol. Wikipedia: Cysteine
Which of the following is an essential amino acid for humans?
Glycine
Leucine
Glutamine
Tyrosine
Leucine is one of the nine essential amino acids that humans must obtain from their diet because we cannot synthesize it. Glycine and glutamine are nonessential since the body can produce them. Tyrosine is conditionally essential, derived from phenylalanine. Wikipedia: Essential amino acid
What is the approximate isoelectric point (pI) of glycine?
2.3
6.0
7.4
9.6
Glycine has only two ionizable groups: its amino and carboxyl groups. The pI is the average of the pKa values of these groups, around (2.34 + 9.60)/2 ? 6.0. At this pH, glycine exists predominantly as a zwitterion with no net charge. Wikipedia: Zwitterion
Which amino acid has an imidazole side chain that can act as a proton donor or acceptor near physiological pH?
Arginine
Histidine
Lysine
Proline
Histidine’s side chain contains an imidazole ring with a pKa near 6.0, allowing it to be protonated or deprotonated around physiological pH. This makes it critical in enzyme active sites for acid–base catalysis. Arginine and lysine have higher pKa values and remain protonated at pH 7.4. Wikipedia: Histidine
Which amino acid has a nonpolar, aliphatic side chain and is often found in the interior of proteins?
Alanine
Aspartate
Lysine
Asparagine
Alanine has a small, nonpolar methyl side chain that makes it hydrophobic and commonly found in protein cores. Aspartate and asparagine are polar or charged, and lysine is positively charged. The simplicity of alanine makes it a helix former in secondary structure. Wikipedia: Alanine
At physiological pH, what is the net charge of the side chain of aspartic acid?
-1
0
+1
+2
Aspartic acid has a carboxyl side chain with a pKa around 3.9, so at pH 7.4 it is fully deprotonated and carries a ?1 charge. The ?-amino and ?-carboxyl groups contribute charges, but the question addresses only the side chain. This negative charge contributes to salt bridges in proteins. Wikipedia: Aspartic acid
Which amino acid’s hydroxyl group commonly acts as a nucleophile in serine protease active sites?
Phenylalanine
Tyrosine
Serine
Tryptophan
Serine proteases, such as trypsin and chymotrypsin, use the hydroxyl of a serine residue to attack peptide bonds. The serine’s –OH is activated by a catalytic triad. Tyrosine also has an –OH but is not used in this context. Wikipedia: Serine protease
A peptide bond is formed between which two functional groups of adjacent amino acids?
Carboxyl and hydroxyl
Amino and carboxyl
Amino and thiol
Carbonyl and carboxyl
Peptide bonds form by a dehydration reaction between the ?-amino group of one amino acid and the ?-carboxyl group of another. This covalent link is also called an amide bond. The reaction releases water and is catalyzed by the ribosome in cells. Wikipedia: Peptide bond
What type of interaction primarily stabilizes an ?-helix in a protein’s secondary structure?
Ionic bonds
Disulfide bonds
Hydrogen bonds
Hydrophobic interactions
Alpha helices are stabilized by hydrogen bonds between the backbone carbonyl oxygen of residue i and the amide hydrogen of residue i+4. These hydrogen bonds run parallel to the helix axis. Side-chain interactions play lesser roles in helix stability. Wikipedia: Alpha helix
Which aromatic amino acid contributes most to a protein’s absorbance at 280 nm?
Phenylalanine
Tyrosine
Tryptophan
Histidine
Tryptophan has the highest molar extinction coefficient among the standard amino acids at 280 nm due to its indole ring. Tyrosine also absorbs but less strongly, and phenylalanine contributes minimally. This property is used to quantify protein concentration. Wikipedia: Tryptophan
Which amino acid is achiral and does not have an L- or D- form?
Alanine
Glycine
Valine
Threonine
Glycine’s side chain is a single hydrogen, making its ?-carbon bonded to two identical substituents. This symmetry removes chirality, so glycine is achiral and has no L/D isomers. All other standard amino acids are chiral (except proline, which is cyclic but still chiral). Wikipedia: Glycine
Why does proline often disrupt ?-helices when incorporated into the polypeptide chain?
Its side chain is too hydrophobic
It forms kinks due to its ring structure
It lacks an amide hydrogen, preventing hydrogen bond donation
Its side chain is charged at physiological pH
Proline’s unique cyclic structure binds its side chain to the backbone nitrogen, so the amide nitrogen lacks a hydrogen for hydrogen bonding. This prevents the backbone N–H group from participating in the helix hydrogen-bonding pattern. Additionally, the ring restricts backbone dihedral angles, causing kinks. Wikipedia: Proline
With a side chain pKa around 6.0, what fraction of histidine imidazole groups are deprotonated at pH 7.4?
10%
50%
96%
30%
Using the Henderson–Hasselbalch equation, the ratio [A–]/[HA] = 10^(pH–pKa) = 10^(7.4–6.0) ? 25. When ratio = 25, about 25/26 ? 96% of imidazole groups are deprotonated. This makes histidine an effective proton shuttle in enzymes. Wikipedia: Histidine acid–base equilibrium
Which dipeptide will carry a net neutral charge at pH 7.0 without additional ionizable side chains?
Lysine–Arginine
Aspartate–Glutamate
Glycine–Glycine
Lysine–Glutamate
At pH 7.0, the terminal ?-amino group is +1 and the terminal ?-carboxyl group is ?1. Glycine–glycine has no ionizable side chains, so these charges cancel for a net zero. Lysine–arginine and lysine–glutamate have charged side chains. Aspartate–glutamate would be overall negative. Wikipedia: Amino acids and zwitterions
For an acid with pKa 4.76, what is the ratio of deprotonated form [A–] to protonated form [HA] at pH 3.76?
0.1
1
10
100
The Henderson–Hasselbalch equation gives pH = pKa + log([A–]/[HA]). At pH 3.76, ?pH = ?1.00 so log([A–]/[HA]) = ?1 and [A–]/[HA] = 0.1. This means the protonated form strongly predominates at a pH one unit below pKa. Wikipedia: Henderson–Hasselbalch equation
What is the approximate isoelectric point (pI) of lysine, given its ?-carboxyl pKa ~2.18, ?-amino pKa ~9.06, and ?-amino pKa ~10.53?
7.4
8.0
9.7
10.5
Lysine has two positively charged groups at physiological pH. The pI is calculated by averaging the two pKa values around the neutral form: (9.06 + 10.53) / 2 ? 9.8. This falls in the basic range, consistent with lysine’s properties. Wikipedia: Isoelectric point
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Study Outcomes

  1. Identify amino acid structures -

    Recognize and name each of the twenty amino acids by analyzing their unique R-group configurations in the amino acid quiz.

  2. Recall amino acid codes -

    Memorize and reproduce the one-letter and three-letter abbreviations for all standard amino acids to strengthen retention.

  3. Differentiate side chain properties -

    Distinguish between polar, nonpolar, acidic, and basic side chains to understand amino acid behavior in biological systems.

  4. Analyze peptide bond formation -

    Examine how individual amino acids link together to form peptides, enhancing comprehension of protein structure.

  5. Apply naming conventions -

    Use IUPAC and common nomenclature rules to systematically name amino acid derivatives and variants in structure quizzes.

  6. Evaluate quiz performance -

    Assess your mastery of amino acid trivia and structures through interactive quiz amino acids challenges, boosting confidence and knowledge.

Cheat Sheet

  1. Side Chain Classification -

    Master the grouping of amino acids into nonpolar, polar uncharged, acidic, and basic classes as taught in university biochemistry curricula. Use the mnemonic "PVT TIM HALL" to recall essential amino acids quickly. This foundational classification appears in many biochemistry quizzes and underpins protein function analysis.

  2. Acid-Base Chemistry & pI Calculation -

    Amino acids have two titratable groups (amino and carboxyl) and sometimes ionisable side chains, each with distinct pKa values from peer-reviewed sources. When tackling an amino acid quiz, calculate the isoelectric point (pI) using the formula pI = (pKaα-carboxyl + pKaα-amino)/2 for neutral amino acids, e.g. glycine pI≈6.0. Remember that acidic and basic side chains require averaging the relevant pKa values for their own pI determination.

  3. Backbone Structure & Chirality -

    Every α-amino acid features an α-amino group, α-carboxyl group, a hydrogen, and a variable R-group bonded to the chiral α-carbon (except glycine). Visualize Fischer projections and L-configuration to predict reactivity and stereospecificity in enzyme-catalyzed reactions, as detailed in core biochemistry texts. Recognizing this backbone setup is essential for drawing structures accurately in structure-based quizzes.

  4. Aromatic Residues & UV Spectroscopy -

    Aromatic amino acids like tryptophan, tyrosine, and phenylalanine absorb UV light at ~280 nm, a principle used in protein quantification assays featured in research repositories. Tryptophan has the highest extinction coefficient, so calculating absorbance can estimate protein concentration using Beer - Lambert Law: A=εlc. Familiarity with these spectral properties is a common theme in both academic exams and lab-based quizzes.

  5. Special Cases: Proline & Disulfide Bonds -

    Proline's cyclic side chain induces kinks in α-helices, often discussed in top-tier journals for its role in protein folding. Cysteine residues form reversible disulfide bonds ( - S - S - ) crucial for tertiary structure stability, a fact highlighted in official biochemical guidelines. A quick mnemonic - "Proline breaks, Cysteine links" - can reinforce their special structural roles in proteins.

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