Biochem 1.2 Amino Acid Properties Overview
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Questions and Answers

At physiological pH, what percentage of histidine side chains are typically protonated and positively charged?

  • 80%
  • 30%
  • 50%
  • Less than 10% (correct)

    • Which of the following amino acids is considered a basic amino acid at physiological pH?

  • Glutamate
  • Aspartate
  • Histidine (correct)
  • Cysteine

    • Which amino acids are classified as acidic amino acids?

  • Arginine and Lysine
  • Cysteine and Histidine
  • Tyrosine and Phenylalanine
  • Aspartate and Glutamate (correct)

    • How do positively charged amino acids mainly acquire their charge?

    <p>By accepting a proton</p> Signup and view all the answers

    Under physiological conditions, which of the following statements is true about lysine and arginine?

    <p>Both are primarily protonated and positively charged</p> Signup and view all the answers

    Which of the following amino acids is predominantly neutral under physiological conditions?

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

    What distinguishes the behavior of histidine at physiological pH compared to lysine and arginine?

    <p>Histidine is predominantly uncharged</p> Signup and view all the answers

    What role do acidic amino acids play in terms of proton interaction?

    <p>They lose protons to their environment</p> Signup and view all the answers

    Which of these amino acids would you classify as a positively charged amino acid?

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

    Which amino acids are classified as branched-chain amino acids (BCAAs)?

    <p>Valine, Leucine, Isoleucine</p> Signup and view all the answers

    What is the primary state of cysteine side chains at physiological pH?

    <p>Predominantly neutral</p> Signup and view all the answers

    What defines aliphatic amino acids?

    <p>They do not contain fully conjugated, aromatic ring structures.</p> Signup and view all the answers

    Which of the following amino acids is considered polar neutral?

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

    Why is tyrosine grouped with aromatic amino acids?

    <p>Its aromatic ring contributes significant nonpolar character.</p> Signup and view all the answers

    Which nonpolar amino acid is an exception to the classification due to its size and charge?

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

    What distinguishes polar neutral amino acids from other categories?

    <p>Their side chains have significant polar character.</p> Signup and view all the answers

    Which of the following amino acids does NOT belong to the aliphatic amino acids group?

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

    Proline is classified as aliphatic despite having a ring because:

    <p>The ring does not introduce significant polarity.</p> Signup and view all the answers

    Which of these amino acids is characterized by a branched chain?

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

    Which factor contributes to the classification of amino acids as aromatic?

    <p>A fully conjugated aromatic ring structure.</p> Signup and view all the answers

    Which amino acids are considered true neutral amino acids?

    <p>Asparagine, glutamine, serine, and threonine</p> Signup and view all the answers

    What characterizes the hydroxyl group of tyrosine compared to other aromatic amino acids?

    <p>It allows tyrosine to be more polar and slightly more hydrophilic.</p> Signup and view all the answers

    Which of the following side chains has a weak dipole moment and cannot hydrogen bond with water?

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

    At physiological pH, which amino acid side chain is slightly more soluble in water than tyrosine?

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

    Which of the following statements about the ionization of amides is true?

    <p>Amides rarely carry a charge in biological contexts.</p> Signup and view all the answers

    Why are phenols easier to deprotonate than other alcohols?

    <p>Because of the accessibility of the hydroxyl group.</p> Signup and view all the answers

    Which amino acid can carry a charge on its side chain, though it is predominantly neutral under physiological conditions?

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

    Which group in cysteine exposes lone electron pairs to facilitate interactions with water?

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

    At physiological pH, how do the charges of tyrosine and cysteine compare?

    <p>Both are predominantly neutral.</p> Signup and view all the answers

    What is a common characteristic of the polar neutral amino acids?

    <p>They have significant dipole moments, making them hydrophilic.</p> Signup and view all the answers

    What primarily determines the unique properties of each amino acid?

    <p>The side chain of the amino acid</p> Signup and view all the answers

    Which characteristic best describes nonpolar amino acids?

    <p>They interact poorly with water.</p> Signup and view all the answers

    Which two nonpolar amino acids contain heteroatoms in their side chains?

    <p>Methionine and Tryptophan</p> Signup and view all the answers

    Which property significantly influences protein interactions with their environment?

    <p>The hydrophobic or hydrophilic nature of amino acid side chains</p> Signup and view all the answers

    What is the main characteristic of the C--C and C--H bonds in most nonpolar amino acids?

    <p>They are nonpolar and do not create a large net dipole.</p> Signup and view all the answers

    In the context of amino acids, what does hydrophobic mean?

    <p>They do not interact well with water.</p> Signup and view all the answers

    What effect does the polar portion of tryptophan's side chain have on its overall classification?

    <p>It has a negligible influence and does not change its classification.</p> Signup and view all the answers

    Why is understanding amino acid properties crucial in biochemistry?

    <p>To predict interactions between proteins and their environments.</p> Signup and view all the answers

    Which classification correctly represents the groups of amino acid side chains?

    <p>Polar, nonpolar, charged</p> Signup and view all the answers

    What type of amino acid is methionine considered due to its side chain composition?

    <p>Nonpolar due to its low electronegativity atoms</p> Signup and view all the answers

    Study Notes

    Amino Acid Properties

    • Twenty proteinogenic amino acids have identical backbones, unique properties arising from their side chains.
    • Side chain properties dictate protein behavior and function.
    • Positively charged side chains interact with negatively charged molecules.
    • Hydrophobic side chains reside in cell membranes.

    Nonpolar Amino Acids

    • Mostly C and H atoms, nonpolar bonds.
    • Poor interaction with water, hydrophobic.
    • Methionine and tryptophan contain heteroatoms (other than C or H).
    • Methionine's sulfur forms a methyl thioether.
    • Tryptophan has a nitrogen atom, polar, but nonpolar overall.

    Aliphatic Amino Acids

    • Nonpolar, non-aromatic.
    • Includes glycine, alanine, methionine, valine, leucine, isoleucine, and proline.
    • Proline has a ring, not aromatic.
    • Valine, leucine, and isoleucine form branched-chain amino acids (BCAAs).

    Aromatic Amino Acids

    • Nonpolar, aromatic rings in their side chains.
    • Includes phenylalanine, tryptophan, and tyrosine.
    • Tyrosine is often considered polar, but its large aromatic ring contributes significantly to its nonpolar character.

    Polar Neutral Amino Acids

    • Side chains have significant polar character but are neutral at physiological pH.
    • Includes asparagine, glutamine, serine, and threonine.
    • These side chains can interact with water.

    Charged Amino Acids

    • Carry electric charges (positive or negative) under physiological conditions.
    • Arginine and lysine are positively charged (basic).
    • Aspartate and glutamate are negatively charged (acidic).
    • Histidine is sometimes categorized as basic, though it's typically neutral under physiological pH.

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    Amino Acid Properties PDF

    Description

    Explore the unique properties of amino acids and their impact on protein behavior and function. This quiz covers nonpolar, aliphatic, and aromatic amino acids, detailing their structure, interactions, and significance in biochemistry.

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