Biochemistry 1.1
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Questions and Answers

What is the central carbon atom in amino acids commonly referred to as?

  • Beta-carbon
  • Amino-carbon
  • Alpha-carbon (correct)
  • Gamma-carbon
  • What is the primary difference between serine and cysteine?

  • Cysteine contains a sulfur atom in its thiol group. (correct)
  • Serine has an additional methyl group attached.
  • Serine has a thiol group instead of a hydroxyl group.
  • Cysteine has an oxygen atom in its structure.
  • Which groups are directly bonded to the α-carbon in proteinogenic amino acids?

  • Amino and carboxyl groups (correct)
  • Carbonyl and keto groups
  • Phosphate and sulfhydryl groups
  • Hydroxyl and methyl groups
  • Which amino acid is nearly identical to serine but includes an extra methyl group?

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

    Which of the following amino acids is considered nonproteinogenic?

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

    What characterizes an amino acid's zwitterionic form in a physiological environment?

    <p>It has no overall electric charge.</p> Signup and view all the answers

    What role do the R-groups or side chains play in amino acids?

    <p>They determine the identity and unique properties of the amino acid</p> Signup and view all the answers

    What distinguishes valine from threonine?

    <p>Threonine has an extra methyl group.</p> Signup and view all the answers

    Which amino acid is considered the simplest due to its side chain structure?

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

    Which amino acid has an amino group located on its γ-carbon?

    <p>β-Alanine</p> Signup and view all the answers

    Which amino acid connects its side chain to both the alpha carbon and the backbone nitrogen?

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

    How are the proteinogenic amino acids categorized?

    <p>By the unique properties of their R-groups</p> Signup and view all the answers

    Which of the following correctly describes alanine's side chain?

    <p>It has a methyl group.</p> Signup and view all the answers

    What is the one-letter code for cysteine?

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

    What happens to the amino acid structure when it is dissolved in aprotic solvents?

    <p>It maintains an electrically neutral form</p> Signup and view all the answers

    Which amino acid structure contains a thiol group?

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

    Why is it important to memorize the structures of each amino acid?

    <p>To recognize their unique properties when forming proteins.</p> Signup and view all the answers

    What functional group does serine contain in its side chain?

    <p>A hydroxyl group</p> Signup and view all the answers

    Which amino acid is specifically noted for playing an important role as an inhibitory neurotransmitter?

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

    Isoleucine has the same molecular formula as which other amino acid?

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

    What is the one-letter code for threonine?

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

    What is the three-letter code for glycine?

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

    Which amino acid has a side chain derived from alanine?

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

    What is the one-letter code for alanine?

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

    What is the one-letter code for aspartate?

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

    Which of the following amino acids contains a carboxylic acid group in its side chain?

    <p>Aspartic Acid</p> Signup and view all the answers

    What is the predominant charge of aspartate under physiological conditions?

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

    Which amino acid is neutral due to the structure of its side chain at physiological pH?

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

    What distinguishes glutamic acid from aspartic acid?

    <p>Number of carbon atoms</p> Signup and view all the answers

    Which amino acid's three-letter code highlights the amide functional group?

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

    Which of the following statements is true regarding the one-letter codes for aspartate and glutamate?

    <p>They are alphabetically sequential in the coding</p> Signup and view all the answers

    Which amino acid contains a methyl thioether group?

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

    What characterizes the structure of lysine at physiological pH?

    <p>It carries a positive charge at the end of a four-carbon chain.</p> Signup and view all the answers

    How can you remember the one-letter code for lysine?

    <p>It is adjacent to L in the alphabet.</p> Signup and view all the answers

    Which amino acid is structurally identical to phenylalanine except for the presence of a hydroxyl group?

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

    What is the one-letter code for phenylalanine?

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

    Which amino acid has a guanidinium group in its structure?

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

    What type of amino acids are primarily found in proteins within living cells?

    <p>L-amino acids</p> Signup and view all the answers

    What do the designations L and D in amino acids indicate?

    <p>Stereochemical configuration relative to L- and D-glyceraldehyde</p> Signup and view all the answers

    Which amino acid is known to have an R-configuration at its α-carbon due to its sulfur side chain?

    <p>L-cysteine</p> Signup and view all the answers

    If one amino acid rotates plane-polarized light clockwise, what can be inferred about its configuration?

    <p>It is a D-amino acid</p> Signup and view all the answers

    Which amino acid has a chiral center in its side chain with an R-configuration?

    <p>L-threonine</p> Signup and view all the answers

    What is the relationship between the rotation of plane-polarized light and the L/D designation of amino acids?

    <p>Some L-amino acids rotate light clockwise</p> Signup and view all the answers

    Which of the following amino acids is primarily present in pathological conditions and is not prevalent in healthy humans?

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

    What does the R/S system refer to in the context of amino acids?

    <p>Stereochemical configuration at the α-carbon</p> Signup and view all the answers

    Study Notes

    Amino Acid Structure

    • Amino acids are the fundamental building blocks of proteins, crucial for nearly all cellular functions.
    • The 20 proteinogenic amino acids are the building blocks for all proteins in organisms.
    • Each amino acid has a unique structure, determining its properties and interactions with other molecules.
    • Amino acids share a common structure, the backbone, made up of an amino group and a carboxyl group, attached to a central alpha-carbon.

    Amino Acid Backbone

    • The backbone consists of an amino group and a carboxyl group (also known as a carboxyl group).
    • The alpha-carbon (α-carbon) is the central carbon atom directly adjacent to the carboxyl group.
    • The R-group, or side chain, differentiates each amino acid. This is the variable part of the structure and dictates the specific properties of each amino acid.

    Side Chains (R-groups)

    • The R-group is attached to the α-carbon.
    • The R-group determines the unique properties of each amino acid.
    • Some amino acids have multiple carbon atoms between the amino and carboxyl group. These are non-proteinogenic amino acids and are not typically found in proteins, but still play important roles.

    Zwitterion Form

    • In aqueous environments (like inside cells, typically near pH 7.4), amino acids often exist as zwitterions.
    • A zwitterion has both a positive and a negative charge, balancing out the overall charge to neutral.
    • In this form, the carboxyl group has lost a proton, while the amino group has gained a proton.

    Amino Acid Classification

    • Amino acids are classified based on the chemical properties of their R-groups categorized by polarity, including polar, nonpolar, acidic, and basic.
    • The polarity influences how the amino acids interact with water and other molecules.

    Three-Letter and One-Letter Codes

    • Amino acids are commonly abbreviated using three-letter codes (e.g., Gly for glycine) and one-letter codes (e.g., G for glycine).
    • Memorizing both codes is essential for understanding protein sequences and structures.

    Specific Amino Acid Examples (with structures)

    • Glycine (Gly/G): Simplest amino acid, with a hydrogen atom as its side chain.
    • Alanine (Ala/A): A methyl group (-CH3) as its side chain.
    • Serine (Ser/S): Contains a hydroxyl group (-OH) on a methylene group.
    • Cysteine (Cys/C): Contains a sulfur atom (-SH) instead of an oxygen atom.
    • Threonine (Thr/T): Similar to serine but with an extra methyl group.
    • Valine (Val/V): Similar to threonine but with a methyl group instead of a hydroxyl group.
    • Leucine (Leu/L): Similar to valine with an extra methylene group.
    • Isoleucine (Ile/I): Same molecular formula as leucine, but the methyl groups are attached to different carbons.
    • Proline (Pro/P): A cyclic structure, unique among amino acids and attaches to the main chain backbone (amino group) in two places.
    • Aspartic Acid (Asp/D)/Aspartate: A dicarboxylic acid with a carboxyl group attached to the methylene group; typically in its deprotonated form (aspartate);
    • Asparagine (Asn/N): Very similar to aspartate, but has an amide group instead of the carboxylic acid group.
    • Glutamic Acid (Glu/E)/Glutamate : Similar to aspartate, but with an extra methylene group; commonly exists as glutamate.
    • Glutamine (Gln/Q): Similar to glutamate but with an amide group
    • Methionine (Met/M): Contains a sulfur atom (methylthioether) attached to the side chain.
    • Lysine (Lys/K): Contains a chain of four methylene groups attached to the a-carbon with an amino group.
    • Arginine (Arg/R): Contains three methylene groups and a guanidinium group.
    • Phenylalanine (Phe/F): Contains a phenyl group attached to the methylene group.
    • Tyrosine (Tyr/Y): Similar to phenylalanine but with a hydroxyl group on the benzene ring.
    • Histidine (His/H): Contains a five-membered aromatic ring (imidazole).
    • Tryptophan (Trp/W): Contains two aromatic rings (the indole ring) in its side chain.

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