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Quizzes > High School Quizzes > Science

Amino Acid Acidity Trivia: Practice Quiz

Test your knowledge with fun review questions

Difficulty: Moderate
Grade: Grade 12
Study OutcomesCheat Sheet
Colorful paper art promoting The Acidic Amino Challenge trivia quiz for biology students.

Which of the following acidic amino acids has a shorter side chain?
Aspartic acid
Glutamic acid
Alanine
Valine
Aspartic acid has only one methylene group before its carboxyl side chain, making it shorter compared to glutamic acid. Alanine and valine are non”acidic amino acids and do not have this extra carboxyl group.
What is the characteristic functional group responsible for the acidic nature of certain amino acids?
Carboxyl group
Amino group
Hydroxyl group
Sulfhydryl group
The carboxyl group can donate a proton, which instills the acid property in these amino acids. Other groups listed do not provide the same acidic characteristics.
At physiological pH, the side chains of acidic amino acids are typically:
Negatively charged
Positively charged
Neutral
Hydrophobic
At pH 7.4, the extra carboxyl groups lose protons, resulting in negatively charged side chains. This property impacts how these amino acids interact in proteins.
Which of the following is NOT considered an acidic amino acid?
Glutamine
Aspartic acid
Glutamic acid
Aspartate
Glutamine is a polar but uncharged amino acid, whereas aspartic acid, glutamic acid, and aspartate possess an extra carboxyl group that makes them acidic. This extra group is responsible for their characteristic negative charge.
The acidic property of acidic amino acids is primarily due to the presence of an extra:
Carboxyl group
Methyl group
Hydroxyl group
Amino group
An extra carboxyl group in the side chain enables these amino acids to donate protons, which is the essence of their acidic nature. This functional group is what differentiates them from other non-acidic amino acids.
What is the approximate pKa of the side chain of aspartic acid?
3.9
6.0
7.4
9.0
The side chain carboxyl group of aspartic acid typically has a pKa around 3.9. At pH values above this, the group becomes deprotonated and carries a negative charge.
What is the approximate pKa of the side chain of glutamic acid?
4.3
2.5
7.0
8.0
Glutamic acid's side chain has a pKa around 4.3, which means that at physiological pH the carboxyl group is largely deprotonated. This deprotonation is essential for its acidic functionality.
At pH 7.4, what is the ionization state of the side chains of aspartic and glutamic acids?
Deprotonated
Protonated
Zwitterionic
Neutral
Since the ambient pH is significantly higher than their side-chain pKa values, aspartic acid and glutamic acid are predominantly deprotonated. This deprotonation results in a negative charge, crucial for their roles in proteins.
How do acidic amino acids contribute to the catalytic activity of certain enzymes?
By donating protons to substrates
By forming strong covalent bonds with substrates
By creating hydrophobic pockets
By initiating peptide bond formation
Acidic amino acids can act as proton donors in enzyme active sites, thus facilitating acid-base catalysis. This proton donation is key to triggering certain chemical reactions during catalysis.
Which property makes acidic amino acids more hydrophilic than nonpolar amino acids?
Their additional carboxyl group
Their bulky side chains
Their ability to form disulfide bonds
Their high aromatic content
The extra carboxyl group in acidic amino acids is polar and capable of hydrogen bonding, enhancing their interaction with water. This results in higher hydrophilicity compared to nonpolar amino acids.
In a globular protein, acidic amino acids are most likely located on the:
Protein surface interacting with water
Hydrophobic core
Transmembrane domains
Disulfide-linked regions
Due to their charged and polar nature, acidic amino acids are typically found on the protein surface where they can interact with the aqueous environment. This placement helps in maintaining protein solubility and proper folding.
Compared to aspartic acid, glutamic acid has an extra methylene group. This difference primarily affects its:
Spatial orientation in protein structures
Ability to form hydrogen bonds
Overall electrical charge
Reaction with oxygen
The additional methylene group in glutamic acid extends its side chain, which can alter how it interacts spatially with other residues within a protein. This affects the overall structure and function of the protein.
Which factor most directly determines the protonation state of acidic amino acid side chains in a protein?
Ambient pH
Temperature
Salinity
Protein chain length
The ambient pH compared to the pKa of the acidic side chain dictates whether the group is protonated or deprotonated. This relationship is fundamental to understanding acid-base behavior in proteins.
Replacing an acidic amino acid with a nonpolar amino acid in a protein can disrupt which type of interaction?
Salt bridges
Hydrogen bonds
Covalent bonds
Peptide bonds
Acidic amino acids contribute to the formation of salt bridges through their negatively charged side chains. Replacing them with nonpolar amino acids removes these electrostatic interactions, potentially destabilizing the protein's structure.
The negative charge present on the side chains of acidic amino acids primarily facilitates the formation of which kind of bonds in proteins?
Ionic bonds
Covalent bonds
Peptide bonds
Hydrogen bonds
The deprotonated carboxyl groups of acidic amino acids carry a negative charge that promotes ionic interactions with positively charged groups. These ionic bonds are crucial for stabilizing tertiary and quaternary protein structures.
In the active site of an enzyme, a glutamic acid residue often acts as a catalytic base. What is the mechanism by which it performs this role?
It abstracts a proton from the substrate
It donates a proton to the substrate
It forms a covalent intermediate with the substrate
It chelates a metal ion to stabilize the substrate
In its role as a catalytic base, glutamic acid abstracts a proton from the substrate, facilitating the reaction. This function relies on its deprotonated state at physiological pH.
How might the substitution of an acidic amino acid with a neutral polar amino acid affect a protein's tertiary structure?
It disrupts electrostatic interactions and salt bridges
It increases the formation of disulfide bonds
It enhances the protein's hydrophobic core
It promotes additional hydrogen bonds in the core
Replacing an acidic residue with a neutral one can interrupt ionic interactions and salt bridges that are critical for maintaining the protein's tertiary structure. This loss of charge-based interactions may lead to altered folding and function.
Which experimental technique is most suitable for analyzing the ionization states of acidic amino acids within proteins?
NMR spectroscopy
X-ray crystallography
SDS-PAGE
Western blotting
NMR spectroscopy is adept at revealing details about the local chemical environment and protonation states of amino acid residues. It allows researchers to observe pKa shifts and the behavior of ionizable groups in proteins.
What is a potential consequence of substituting an acidic amino acid with a basic amino acid in an enzyme's active site?
Altered substrate binding leading to loss of function
Improved enzyme specificity
Enhanced thermal stability of the enzyme
No significant change in enzyme activity
Swapping an acidic amino acid for a basic one changes the charge distribution within the active site. This can disrupt substrate binding and alter the enzyme's catalytic efficiency, often resulting in a loss of function.
In peptide drug design, why might acidic amino acids be intentionally included in the sequence?
To improve solubility and facilitate ionic interactions
To strengthen the hydrophobic regions in the peptide
To promote rapid degradation in the body
To decrease overall polarity of the peptide
Acidic amino acids, with their negatively charged side chains, enhance peptide solubility and enable specific ionic interactions. These properties are valuable for improving drug delivery and bioavailability in peptide therapeutics.
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Study Outcomes

  1. Understand the chemical properties and structural roles of acidic amino acids.
  2. Analyze how acidic amino acids influence protein structure and function.
  3. Interpret pH's impact on the ionization state of acidic amino acids.
  4. Apply biochemical principles to distinguish between acidic and other amino acids.
  5. Synthesize experimental data to evaluate the behavior of acidic amino acids in biological systems.

Amino Acid Trivia - Acidity Cheat Sheet

  1. Acidic Side Chains - Acidic amino acids like aspartic acid and glutamic acid feature carboxylic acid groups in their side chains, giving them the power to donate protons and act as acids in biological systems. Their unique chemistry makes them essential players in protein folding and function. aatbio FAQ
  2. Negative Charge at Physiological pH - At around pH 7.4, the carboxyl side chains of acidic amino acids lose a proton, resulting in a net negative charge. This charge influences how proteins interact with each other and with other biomolecules in the cell's bustling environment. Arizona Biology Problem Set
  3. Key pKa Values - Aspartic acid has a side chain pKa near 3.9, while glutamic acid sits around 4.3, meaning they readily give up protons in mildly acidic environments. These pKa values are crucial for predicting when and where these residues will carry a charge. Wikipedia on Protein pKa
  4. Salt Bridges and Stability - When a negatively charged acidic residue meets a positively charged partner, they can form a salt bridge that acts like a molecular glue, stabilizing a protein's 3D shape. These interactions are vital for keeping enzymes and structural proteins in tip‑top form. ReadChemistry Properties Guide
  5. Biosynthesis Roles - Aspartic and glutamic acid aren't just structural heroes; they also serve as starting materials in the creation of other amino acids and nucleotides. This makes them central hubs in metabolic pathways, fueling growth and replication. ScienceInfo Comparison
  6. Influencing Enzyme Activity - The ionization state of acidic residues can turn an enzyme's activity up or down by altering the active site's charge landscape. Think of them as tiny switches that can flip on catalytic power - or dial it back. Pearson Acid‑Base Properties
  7. Predicting Protein Behavior - By understanding whether an acidic residue is protonated or deprotonated at a given pH, you can forecast a protein's solubility, binding affinity, and even its overall shape. It's like having a molecular weather report for your proteins. Pearson Acid‑Base Properties
  8. Isoelectric Point Insights - Acidic amino acids have lower isoelectric points than neutral ones, meaning they reach a net zero charge at more acidic pH values. This helps you predict how proteins will migrate in an electric field during techniques like isoelectric focusing. ScienceDirect Overview
  9. Active Site Stars - Many enzymes tuck acidic residues into their active sites to facilitate proton transfers during reactions. This proton give-and-take is the secret sauce behind countless biochemical conversions. ReadChemistry Properties Guide
  10. Handy Mnemonic - Remember "Asp and Glu are Acidic" by noting both start with a vowel followed by 'sp' or 'lu,' and both carry extra O's for extra acidity! It's a simple trick to keep these acidic all-stars top of mind.
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